1 Departments of Surgery and Physiology, The aim of this
study was to investigate whether the blockade of L-type
Ca2+ channels with verapamil
suppresses giant migrating contractions (GMCs) and therefore diarrhea
during small intestinal inflammation. Small intestinal inflammation was
induced by infection with the nematode Trichinella
spiralis. T. spiralis
infection alone significantly increased the frequency of GMCs and
decreased the frequency of phase III activity in the small intestine
for 9 days. The increased frequency of GMCs was associated with
diarrhea. Immunohistochemical staining with specific antibodies
indicated that the number of neutrophils and mast cells increased
significantly in the jejunal lamina propria during T. spiralis infection. Only the neutrophils increased
significantly in the muscularis externa of the jejunum. Myeloperoxidase
(MPO) activity increased significantly in the jejunal and ileal lamina
propria. Daily verapamil administration during T. spiralis infection significantly reduced the frequency of GMCs and diarrhea but had no further significant effect on the
already reduced frequency of phase III activity. Verapamil administration, however, did not reduce MPO activity or immunocyte infiltration in the jejunum or ileum. We conclude that blockade of
L-type Ca2+ channels selectively
reduces the frequency of GMCs and therefore diarrhea during small
intestinal inflammation. The decreased frequency of GMCs is not
secondary to a reduction in the inflammatory response.
gastrointestinal motility; small intestinal infection; calcium
channel blockers; Trichinella
spiralis; giant migrating contraction; migrating motor
complex; immunocytes
CALCIUM plays an important role in the physiology and
pathophysiology of numerous cell types, including the gut smooth muscle cells and the enteric neurons. In smooth muscle cells, an increase in
cytosolic free Ca2+ concentration
([Ca2+]i)
is an essential step for the cells to contract. Similarly, an increase
in
[Ca2+]i
in the enteric neurons mediates the release of neurotransmitters by
exocytosis (40). The increase in
[Ca2+]i
occurs by influx from the extracellular medium and by
Ca2+ release from the rapidly
exchanging intracellular stores (22). Ca2+ influx occurs through ion
channels in the plasmalemma. The opening of these channels in smooth
muscle cells is regulated by membrane depolarization
[voltage-operated channels (VOCs)] and by receptor activation (receptor-operated channels) (24).
The gastrointestinal smooth muscle cells generate several different
types of contractions to perform the complex motility functions of
mixing and propulsion (33). These include rhythmic phasic contractions,
ultrapropulsive contractions, and an increase in tone (33). In the
small intestine, the rhythmic phasic contractions, organized as
migrating motor complexes (MMC), keep the upper gastrointestinal tract
free of debris and limit bacterial overgrowth to the distal small
intestine during the interdigestive state. In the postprandial state,
the phasic contractions perform the mixing and orderly slow distal
propulsion of the ingested meal. The precise physiological role of an
increase in tone in circular muscle cells is not known. However, it is
possible that the decrease in the diameter of the lumen due to a
sustained increase in tone may enhance the effectiveness of phasic
contractions in mixing and propulsion of chyme.
The ultrapropulsive contractions in the small intestine consist of
giant migrating contractions (GMCs) and retrograde giant contractions
(RGCs). In the normal state, GMCs occur once or twice a day in the
terminal ileum and produce mass movements that may extend into the
proximal colon (30, 32, 33). During intestinal inflammation, the
frequency of GMCs is increased dramatically and the frequent mass
movements in the fasting as well as the postprandial state result in
diarrhea (1, 5, 13, 14, 27). Under certain conditions, GMCs may also
produce abdominal pain (15, 30, 31). RGCs rapidly regurgitate the
contents of the upper small intestine into the stomach in preparation
for vomitus expulsion (18).
It is remarkable that the same circular smooth muscle cells can
generate so many different types of contractions using a limited number
of signal-transduction pathways. The force and duration of contractions
generated by smooth muscle cells are related to the increase in
[Ca2+]i
(36). The amplitude of GMCs is two to three times greater and their
duration four to six times longer than the corresponding parameters of
phasic contractions in phase III activity (30). This suggests that a
GMC may require a much greater increase in [Ca2+]i
than a phasic contraction. Our hypothesis, therefore, is that partial
or complete inhibition of one of the sources of
Ca2+, such as
Ca2+ influx, may affect the
occurrence of GMCs more than it affects the occurrence of the phasic
contractions. If so, Ca2+ channel
blockers may reduce diarrhea associated with GMCs without having a
major effect on the occurrence of phasic contractions and the motility
functions that these contractions perform.
Ca2+ is a ubiquitous intracellular
messenger. The blockade of Ca2+
channels may also affect the infiltration and activation of
immunocytes. Given that
Ca2+ channel blockade may
selectively reduce the frequency of GMCs, we also sought to determine
whether Ca2+ channel blockade is
secondary to a reduction in the inflammatory response or due to a
direct effect of the blockade of
Ca2+ channels in the neuromuscular
circuitry of the small intestine.
Surgical Procedure
ABSTRACT
Top
Abstract
Introduction
Methods
Results
Discussion
References
INTRODUCTION
Top
Abstract
Introduction
Methods
Results
Discussion
References
METHODS
Top
Abstract
Introduction
Methods
Results
Discussion
References
Induction of Small Intestinal Inflammation by Trichinella Spiralis Infection
Male mice (CF-1) were used to maintain a stock infection of the nematode T. spiralis. Each mouse was fed 500 larvae orally. The larvae were allowed to mature in the mouse for at least 30 days before they were used to infect the dogs. The larvae were recovered from the mice by pepsin digestion of skeletal muscle, as described previously by Castro and Fairbain (3). Each dog was fed 2 × 104 larvae/kg mixed with 50 g canned dog food.Experimental Protocol
Each experiment was done after an overnight fast. Primary infection with the nematode T. spiralis occurs only once in each dog. Therefore, two separate groups of five dogs each were used. One group received T. spiralis alone, and the other received verapamil plus T. spiralis (Fig. 1). Preinfection control recordings were made for 1 wk from each dog.
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Dogs in the first group (T. spiralis infection alone) were fed the larvae on Monday morning after one MMC was recorded in the duodenum to establish the interdigestive state. Daily 6-h recordings were made Monday to Friday for the next 2 wk (Fig. 1). The 2-wk recording period was chosen because the abnormal motility patterns and clinical symptoms of T. spiralis infection last for about 10 days (5, 6).
In the second group of dogs (T. spiralis infection plus verapamil), the effect of
verapamil alone was first determined (Fig. 1). Control recordings were
made for 1 wk. An intravenous infusion of 20 µg · kg1 · min
1
verapamil was started 15 min after the occurrence of an MMC in the
duodenum on Monday morning. The infusion and recordings were continued
for 6 h. The dogs were orally fed a 120-mg tablet of verapamil at the
end of the infusion and fed another tablet in the evening at 10 PM.
This schedule was followed from Monday to Friday of the first week and
on Monday and Tuesday of the second week. The dogs received 120-mg
tablets of verapamil three times per day on Saturday and Sunday. The
recordings of motor activity were made for 6 h daily.
Control recordings were made daily during the next week to establish that no effect of verapamil was left over (Fig. 1). On the following Monday, verapamil treatment was resumed (Fig. 1). The dogs were also infected with the nematode T. spiralis. Dogs were fed the larvae 1 h after the start of verapamil infusion. Verapamil treatment continued until Tuesday of the following week. Daily 6-h recordings were made until the end of the second week.
Data Analysis
The recordings were made on a 12-channel Grass pen recorder. The lower and upper cutoff frequencies were set at direct current and 15 Hz, respectively. All data were analyzed visually. Each dog exhibited spontaneous MMC cycles consisting of four phases during the interdigestive state. Phase III activity was defined as a group of contractions occurring at maximum frequency; the group of contractions propagated as a whole in the caudad direction. The contractions in each group lasted for at least 6 min. Phase I had little or no contractile activity. Phase II had intermittent contractions and began when the average frequency of contractions over a 5-min period exceeded 10% of the maximum frequency during phase III activity. Phase IV was the period of transition from phase III to phase I and usually lasted 1-4 min. The interdigestive motor activity in the stomach also consisted of four phases as described above. Phase III activity in the stomach was defined as a series of clusters of one to seven contractions each, such that the quiescent period between successive clusters did not exceed 3 min. The maximum amplitude of at least one contraction in each cluster was greater than twice the mean amplitude of contractions in the preceding gastric phase II activity. The frequency of phase III activity in the small intestine and the stomach was determined by dividing the total number of phase III activities by the duration of the recording.The GMC is a large-amplitude (2-3 times the amplitude of phase III contractions) and long-duration (4-6 times the mean duration of phase III contractions) contraction that rapidly propagates (~1 cm/s) in the caudad direction from the point of its origin. GMCs are ultrapropulsive and have been associated with diarrhea and abdominal cramping (5, 13, 14, 15, 27, 30, 31, 38). RGCs are also contractions of large amplitude (2-3 times the amplitude of phase III contractions) and long duration (2-3 times the duration of phase III contractions). RGCs usually originate in the mid-small intestine and propagate in the orad direction at a velocity of ~10 cm/s (18).
The mean maximum amplitude of contractions in phase III activity and the duration of phase III activity were quantified at three locations. The first transducer in the small intestine represented the duodenum, the seventh transducer represented the ileum, and the fourth transducer represented the jejunum. The mean maximum amplitude was determined by averaging the amplitudes of five maximum-amplitude contractions in phase III activity.
The data were analyzed in four periods: preinfection (5 days of recordings in the normal state), peak infection (days 2-5 postinfection), late infection (days 8 and 9 postinfection), and recovery (days 10-12 postinfection) (Fig. 1).
Measurement of Heart Rate and Blood Pressure
In four dogs, a Statham pressure transducer (model P23XL; Spectramed, Oxnard, CA) was implanted in the external carotid artery under general anesthesia (30 mg/kg Nembutal). Heart rate was monitored by electrocardiogram electrodes attached to the shaved skin.Immunohistochemical Methods and Myeloperoxidase Assay
Immunohistochemical methods. Full-thickness intestinal tissues were obtained from five normal dogs with T. spiralis infection alone and five dogs treated with T. spiralis and verapamil as described above. The tissues were harvested under general pentobarbital sodium anesthesia (30 mg/kg iv). The tissues from the dogs with T. spiralis infection or T. spiralis infection plus verapamil were removed on day 4 postinfection, when the abnormal motility response was nearly maximum (5, 6).
Freshly removed segments of the jejunum (15-20 cm from the ligament of Treitz) and ileum (20-30 cm from the ileocolonic junction) from anesthetized dogs were rinsed thoroughly with ice-cold phosphate-buffered saline (PBS), cut along the mesenteric border, pinned flat to their original dimension, and fixed in 4% picroformaldehyde solution at pH 7.4 for 24 h. The tissues were then rinsed in PBS three or four times. Immunohistochemical processing and analysis were done as described previously (14, 39). Three to four 10-µm cryosections were placed onto a gelatin slide. At least five slides from each dog were incubated with primary antibodies for 4 h at room temperature. Nonspecific antibodies were blocked with 5% goat serum for 30 min. The second antibody, rhodamine isothiocyanate, was visualized with the use of ultraviolet excitation at 520 nm after incubation at room temperature for 1 h. All immunocytes were counted blindly by one person (C. Singaram). Antibodies against B lymphocytes (CD3), T lymphocytes (CD4), interleukin-2 receptor (IL-2R) cells, neutrophils (CD11), activated dendritic cells [reactivated follicular dendritic cell marker 1 (RFD1)], and the human leukocyte antigen DR-1 (HLADR)-positive cells were used. All immunocyte antibodies were purchased from Becton Dickinson (San Jose, CA) and used at 1:10 dilution. The number of immunocytes in the lamina propria and muscularis externa was counted per 10 villi or crypts under ×20 ultraviolet excitation of an Olympus BH2 microscope. Several lengths spanning 10 villi or crypts were counted from each section.Mast cells. A newly developed and characterized antitryptase polyclonal antibody raised in rabbit was used (kindly provided by Promega, Madison, WI) at 1:500 dilution (4). This primary antibody was incubated for 2 h at room temperature. Goat anti-chicken immunoglobulin G conjugated to tetramethylrhodamine was incubated for 2 h at room temperature and, after thorough rinsing with PBS, visualized at 573 nm. Quantitation of the number of positive cells was performed by the method described for other inflammatory cells. This antibody was previously found to be specific by neutralization experiments (using tryptase) and is known to stain both granulated and degranulated mast cells. Also, this antibody appears to stain both mucosal and vascular types of mast cells. We elected to use this antibody because we wanted to know the change in the total number of mast cells in our experimental condition.
Myeloperoxidase estimation. Myeloperoxidase (MPO) assay was performed by the method of Krawisz et al. (16). Briefly, tissue samples were weighed and homogenized with hexadecyltrimethylammonium bromide (HTAB) buffer (0.5% HTAB in 50 mM phosphate buffer, pH 6.0, 4°C). The homogenates were freeze-thawed three times and then centrifuged at 35,000 g for 30 min. The pellets were discarded, and the supernatants were assayed for soluble protein and for MPO activity. MPO activity was measured by adding 0.1 ml supernatant to 2.9 ml reaction buffer [50 mM phosphate buffer, pH 6.0, containing 0.167 mg/ml o-dianisidine hydrochloride (Sigma, St. Louis, MO) and 0.0005% hydrogen peroxide]. After 1 min, the change in absorbency at 460 nm was measured. One unit of MPO activity was defined as that degrading 1 µmol of peroxide per minute at 25°C. The MPO activity was expressed per gram of protein. Soluble protein in the tissue supernatant was assayed using a protein assay kit (Pierce, Rockford, IL) as originally described by Lowry et al. (20).
Scoring of stools. The stool consistency was scored on a scale of 1 to 5: 1 = watery stools; 2 = soft unformed stools; 3 = normal formed stools; 4 = hard stools of small caliber; 5 = no stools. The frequency of stools could not be analyzed reliably because liquid stools tended to mix, and dogs may soil at multiple locations during the same defecation. A score below 2.0 was defined as diarrhea and above 3.5 as constipation. The threshold for constipation and diarrhea is uneven around the normal stool score because total absence of stools with a score of 5 was a much less common occurrence than the incidence of liquid stools. Liquid stools and the minimum score of 1.0 can occur for several days in a row.
Statistical Analysis
All data are expressed as means ± SE. All normally distributed data were analyzed by analysis of variance. Multiple comparisons were done by Fisher's least-square difference method. Student's t-test was used for the comparison of two means. Nonparametric Student-Newman-Keuls test was used for data that did not pass the normality test. A P value of <0.05 was considered statistically significant. The study was approved by the Animal Studies Committee at the Zablocki Veterans Affairs Medical Center. ![]() |
RESULTS |
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Clinical Symptoms
The mean stool scores in the preinfection state in the two groups of dogs, one receiving T. spiralis infection alone and the other receiving T. spiralis infection plus verapamil, were not different from each other (n = 5). Both scores indicated normal formed stools (Fig. 2). The stool score fell below 2.0 (P < 0.05) on days 2-5 and days 8 and 9 in dogs that received T. spiralis infection alone, indicating diarrhea. The stool score on days 10-12 in these dogs was still less than that in the normal state, but it was above the score of 2.0, indicating recovery.
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The stool score in dogs infected with T. spiralis and given verapamil did not fall below 2.0 in any postinfection period (n = 5; Fig. 2). During each postinfection period, the stool score in verapamil-treated dogs was significantly closer to normal than in dogs not treated with verapamil (Fig. 2).
The daily caloric intake decreased significantly during days 2-5 in dogs treated with T. spiralis infection alone as well as in dogs treated with T. spiralis and verapamil (Fig. 3). There was no significant difference in daily caloric intake between verapamil-treated and non-verapamil-treated dogs during any postinfection period (n = 5; Fig. 3).
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Verapamil infusion significantly decreased the mean systolic blood pressure by ~18% and increased the heart rate by ~40% (Table 1) at the end of the 6-h infusion period on day 1 (n = 4). Similar changes occurred during verapamil infusion in dogs infected with the nematode T. spiralis (Table 1). The blood pressure and heart rate on subsequent days were stable around the values seen at the end of the 6-h infusion period on day 1.
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MPO Activity and Immunohistochemical Findings
Changes in immunocyte infiltration. The number of neutrophils and mast cells increased significantly in the lamina propria of the jejunum on day 4 of T. spiralis infection (Fig. 4; Table 2). This was also the time when the maximum effects of inflammation on motility patterns were seen (Fig. 4; Table 2). Ileal lamina propria exhibited a significant increase of T lymphocytes only (Table 2). Only neutrophils were found to increase in the jejunal muscularis externa of T. spiralis-treated dogs (Fig. 4; Table 2). The immunocyte infiltration in dogs treated with verapamil and T. spiralis was not different from those treated with T. spiralis alone, except for mast cells, which were significantly greater in the lamina propria of the ileum in dogs treated with T. spiralis plus verapamil than in dogs treated with only T. spiralis infection (Table 2). All other immunocytes, i.e., B lymphocytes, IL-2R, HLADR, and RFD1 cells, did not exhibit any significant change in T. spiralis or T. spiralis plus verapamil-treated dogs.
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MPO activity. MPO activity increased significantly in the lamina propria of the jejunum and the ileum on day 4 of infection in both groups of dogs (Table 3). There was no significant difference between the dogs that received T. spiralis infection alone and the dogs that received T. spiralis infection plus verapamil. The MPO activity increased in the muscularis externa of the jejunum in dogs treated with verapamil and T. spiralis (Table 3).
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Effect of T. Spiralis-Induced Inflammation on Gastrointestinal Motor Activity
Small intestinal inflammation due to T. spiralis infection significantly decreased the frequency of phase III activity in the stomach and the whole small intestine on days 2-5 and days 8 and 9 postinfection (n = 5; Fig. 5). The frequency of phase III activity in the small intestine, but not in the stomach, recovered on days 11 and 12 postinfection.
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The frequency of GMCs increased significantly during intestinal inflammation induced by T. spiralis infection (Figs. 6A and 7). The dogs were often uncomfortable when GMCs occurred in the small intestine. The increase in the frequency of GMCs was significant on days 2-5 and days 8 and 9 postinfection.
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Small intestinal inflammation increased the frequency of RGCs on days 2-5 only (Fig. 8).
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Effect of Verapamil Administration Alone on Gastrointestinal Motor Activity
Verapamil administration alone significantly decreased 1) the frequency of phase III activity in the stomach and the duodenum but not in the jejunum and the ileum (Table 4); 2) the mean duration of phase III activity in the stomach, duodenum, and ileum (n = 5; Table 3); 3) the maximum amplitude of phase III contractions in the jejunum and the ileum (Table 3); and 4) the percentage of phase I activity in the MMC cycle of the stomach, duodenum, jejunum, and ileum (Table 4).
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Effect of Verapamil on Abnormal Motor Activity During Small Intestinal Inflammation Induced by T. Spiralis Infection
Although verapamil decreased the frequency of phase III activity in the small intestine in the normal state, it had no further effect on the already reduced frequency of phase III activity in the inflamed state (n = 5; Fig. 5). In the stomach, verapamil had no further effect on the already reduced frequency of phase III activity on days 2-5, but on days 8 and 9 the frequency of phase III activity in verapamil plus T. spiralis-treated dogs was less than that in dogs treated with T. spiralis alone (Fig. 5).The frequency of GMCs in verapamil plus T. spiralis-treated dogs was significantly less than that in T. spiralis-treated dogs on days 2-5 and days 8 and 9 (Figs. 6B and 7). However, verapamil had no significant effect on the distance of origin of GMCs from the ileocolonic junction and the distance of their propagation (n = 5; Table 5).
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Administration of verapamil during T. spiralis infection did not reverse the increase in the frequency of RGCs on days 2-5 postinfection (Fig. 8).
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DISCUSSION |
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Our findings show that blockade of L-type Ca2+ channels by verapamil significantly inhibits the frequency of GMCs during small intestinal inflammation without having a significant further effect on the already reduced frequency of phase III activity. GMCs are large-amplitude and long-duration contractions that rapidly propel small intestinal, pancreatic, and biliary tract secretions in the fasting state and undigested food in the postprandial state into the colon to increase its osmotic load (6, 27, 30). During small intestinal inflammation, the GMCs originating in the small intestine also propagate into the colon to produce frequent colonic mass movements (14, 26, 35). Both factors contribute to diarrhea. The frequency of GMCs has also been reported to increase in human small intestinal inflammation during Salmonella and gram-negative bacilli infections (1, 13) and in animal models of inflammation including radiation enteritis (27), T. spiralis infection (5), and mucosal exposure to ethanol and acetic acid (14). Inflammation in all of these states produces diarrhea and abdominal cramping. The reduction in the frequency of GMCs by verapamil during small intestinal inflammation induced by T. spiralis infection significantly reduced diarrhea. In contrast, verapamil had no significant effect on anorexia during T. spiralis infection.
Although GMCs and RGCs are both giant contractions, there are significant differences in their characteristics. The RGCs propagate in the orad direction at a velocity of ~10 cm/s (17), whereas GMCs propagate in the caudad direction at a velocity of ~1 cm/s. The RGCs generally originate at about the mid-small bowel, but the GMCs can originate anywhere in the small intestine (5, 27, 30). The duration of GMCs is about four to six times longer and that of RGCs about two to three times longer than the duration of phase III contractions. Our data suggest that the dependence of the two types of giant contractions on Ca2+ influx through L-type channels may be markedly different. Verapamil reduced the frequency of GMCs but not that of RGCs during small intestinal inflammation.
T. spiralis infection in rats induces inflammation mainly in the proximal small intestine (2, 23). The MPO activity in T. spiralis-infected rats increases in the proximal jejunum but not in the ileum. Our data show that in dogs, small intestinal inflammation due to T. spiralis infection may be more generalized. MPO activity increased in both the jejunum and the ileum. The stimulation of GMCs during inflammation is thought to be due to the modulation of the enteric neural and cellular mechanisms of control of contractions by the inflammatory response mediators. The increase of inflammatory cells throughout the small intestine is consistent with our finding that GMCs originate almost anywhere in the small intestine during T. spiralis infection. During inflammation induced by mucosal exposure to ethanol and acetic acid in the ileum alone, the GMCs originate mainly in the inflamed segment (14).
Although verapamil reduced the frequency of GMCs, it did not reduce the inflammatory response as measured by MPO activity or the infiltration of inflammatory cells. These data suggest that the reduction in the frequency of GMCs and accompanying diarrhea may be a direct effect of blocking Ca2+ channels in enteric neurons and smooth muscle cells rather than due to a reduction of the inflammatory response. The activation of nonexcitable immunocytes is also accompanied by an increase in [Ca2+]i that is partially due to Ca2+ influx. However, the precise nature and regulation of ion channels through which influx occurs in nonexcitable cells are not understood completely. There is strong evidence that Ca2+ influx in leukocytes or lymphocytes is not due to Ca2+ influx through voltage-gated ion channels (8, 10, 11). 1) The depolarization of leukocytes by high K+ that opens voltage-gated Ca2+ channels does not in itself increase [Ca2+]i. 2) Blockade of voltage-dependent Ca2+ channels does not block agonist-induced Ca2+ influx in lymphocytes. Ca2+ influx in the inflammatory cells is thought to occur through voltage-independent second messenger-operated channels (9). These data support our finding that verapamil did not reduce the inflammatory response to suppress abnormal motility.
Ca2+ influx through L-type channels plays an important role in the occurrence of in vivo phasic contractions as well as GMCs (34, 37), in vitro phasic contractions of muscle strips (28), and increased tone in dissociated single smooth muscle cells (12, 17, 25, 41). The precise sources of Ca2+ utilized to stimulate GMCs are not understood completely. However, Ca2+ influx through VOCs has been reported to play an important role in the stimulation of GMCs (34). Spontaneous membrane depolarizations are obliterated during a GMC, probably due to a sustained depolarization of the cell membrane (30). This depolarization may open VOCs. Also, GMCs induced by close intra-arterial infusions of caffeine are blocked by verapamil (34). Thus, whereas Ca2+ influx through VOCs plays an important role in the stimulation of both phasic contractions and GMCs, our present data show that the sensitivity of this influx for the stimulation of the two types of contractions may be different. At the dose of verapamil used in our study, the frequency of GMCs was inhibited significantly, whereas there was no concurrent additional effect on MMC cycling that had already been decreased by inflammation.
The inhibition of Ca2+ influx in the normal state produced a heterogeneous response in the gastrointestinal tract. Verapamil significantly decreased the frequency of phase III activity in the stomach and the duodenum but not in the jejunum and the ileum. On the other hand, the maximum amplitude of contractions in phase III activity decreased in the jejunum and the ileum but not in the stomach and the jejunum. These data suggest that the role of Ca2+ influx through VOCs to stimulate phase III activity may differ in the upper and lower gastrointestinal tract. A difference in the sensitivity of L-type Ca2+ channels to stimulate tone in isolated segments of the duodenum and colon has also been reported previously (21).
We expected verapamil to increase the duration of phase I activity by inhibiting phase II contractions. However, the duration of phase I activity after verapamil decreased throughout the gastrointestinal tract. Lang et al. (19) reported previously that phase I activity is produced by an ascending inhibitory reflex stimulated by the distally propagating phase III activity. Verapamil significantly decreased the amplitude and duration of phase III contractions. The decrease in the duration of phase I activity may be due to the partial inhibition of phase III activity and hence the intensity of the ascending inhibitory reflex.
DePonti et al. (7) reported that intravenous infusion of ~17
µmol · kg1 · min
1
verapamil for 3 h almost completely abolished MMC cycling. We found
that this inhibition occurs only in the stomach and the duodenum, and
not in the distal small intestine. In contrast, Thollander et al. (42)
reported no significant effect of verapamil on MMC cycling in rats.
The dose of verapamil used in our study decreased the systolic blood pressure by ~20% and increased heart rate by ~40%. The dogs did not exhibit any apparent signs of discomfort or uneasiness during verapamil treatment.
In conclusion, in dogs, inflammation due to T. spiralis infection occurs throughout the small intestine. Verapamil, an L-type Ca2+ channel blocker, significantly inhibits GMCs during inflammation without a concurrent effect on the already decreased frequency of phase III activity. The selective inhibition of GMCs reduces diarrhea. The inhibition of GMCs by verapamil seems to be a direct effect of L-type Ca2+ channel blockade on smooth muscle cells and enteric neurons rather than due to a reduction of the inflammatory response. The L-type Ca2+ channel blockers may have a potential therapeutic role in minimizing diarrhea and abdominal cramping during small intestinal inflammation.
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ACKNOWLEDGEMENTS |
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This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grant DK-32346 (S. K. Sarna), the Department of Veterans Affairs Research Service (S. K. Sarna and C. Singaram), the American Federation for Aging Research, and the United States Binational Scientific Foundation (C. Singaram). C.-W. Lee was supported in part by a fellowship from the Advisory Board of the Digestive Disease Research Center at the Medical College of Wisconsin.
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FOOTNOTES |
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Address for reprint requests: S. K. Sarna, Dept. of Surgery, Medical College of Wisconsin, 9200 West Wisconsin Ave., Milwaukee, WI 53226.
Received 15 April 1996; accepted in final form 16 June 1997.
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