Department of Oral Biology and Oral Science Research Center, Brain Korea 21 Project for Medical Science, Yonsei University College of Dentistry, Seoul, Korea
Submitted 5 December 2002 ; accepted in final form 9 July 2003
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ABSTRACT |
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cholecystokinin; plasma membrane adenosine 5'-triphosphatase; G proteins; caffeine
Physiological concentrations of hormones and neuro-transmitters usually evoke [Ca2+]i oscillations, which are generated primarily by repetitive Ca2+ release from IP3-sensitive Ca2+ stores. This phenomenon does not generally require Ca2+ influx; thus, in rat pancreatic acinar cells, low concentrations of cholecystokinin (CCK) induce [Ca2+]i oscillations, which continue for some time in the absence of extracellular Ca2+ (20, 24).
Direct activation of G proteins by AlF4- has also been shown to induce [Ca2+]i oscillations in a variety of cell types (12, 18, 25). AlF4- binds to the -subunit of heterotrimeric G proteins and forms a complex with G
·GDP, which leads to the activation of G proteins and downstream signaling cascades (3). Therefore, the characteristics of AlF4--evoked [Ca2+]i oscillations are thought to be similar to those of agonist-evoked oscillations. However, in rat pancreatic acinar cells, a fundamental difference was reported between AlF4-- and CCK-evoked [Ca2+]i oscillations; i.e., removal of Ca2+ from the perfusate resulted in a rapid termination of AlF4--evoked [Ca2+]i oscillations (25). This result suggested that, in contrast to CCK-evoked [Ca2+]i oscillations, [Ca2+]i oscillations caused by AlF4- acutely depend on extracellular Ca2+. Because [Ca2+]i oscillations caused by CCK and AlF4- are known to be generated through the same signaling pathway leading from G proteins to IP3 generation, the different sensitivities to extracellular Ca2+ of AlF4-- and CCK-evoked [Ca2+]i oscillations remain to be explained. Therefore, in the present study, we examined the mechanisms by which AlF4- generates extracellular Ca2+-dependent [Ca2+]i oscillations in rat pancreatic acinar cells.
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METHODS |
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[Ca2+]i measurements. Cells were loaded with fura 2 by incubation with 2 µM fura 2-acetoxymethyl ester in HEPES-buffered solution equilibrated with 100% O2 for 40 min at room temperature. They were washed twice and resuspended in an HCO3--buffered solution containing (in mM) 110 NaCl, 4.5 KCl, 1.0 NaH2PO4, 1.0 MgSO4, 1.5 CaCl2, 25 NaHCO3, 5 HEPES-Na, 5 HEPES free acid, and 10 D-glucose and equilibrated with 95% O2-5% CO2 to give pH 7.4. The cells were allowed to attach to a coverslip, which formed the base of a cell chamber mounted on the stage of an inverted microscope. Once the cells had adhered to the coverslip, they were continuously superfused with the HCO3--buffered solution at a flow rate of 2 ml/min. In experiments involving caffeine, 10 mM NaCl was replaced by 20 mM caffeine. In Ca2+-free solutions, CaCl2 was omitted and 1 mM EGTA was added. Because Al3+ binds to EGTA with high affinity, 1 mM EGTA-containing Ca2+-free solutions were supplemented with 1 mM AlCl3 to allow a free Al3+ concentration of 100 nM. Free Al3+ concentration was calculated using Maxchelator software (C. Patton, Stanford University, Stanford, CA). All experiments were carried out at 37°C. [Ca2+]i was measured by spectrofluorometry (Photon Technology International, Brunswick, NJ), with excitation at 340 and 380 nm and emission at 510 nm. The values of [Ca2+]i were calculated using the equation previously described (6).
Isolation of microsomes from rat skeletal muscle. The microsomal fraction of the rat skeletal muscle was obtained using a modification of a method described previously (9). Fresh skeletal muscles were dissected and then cut into small pieces. Tissues were homogenized in ice-cold solution containing 10 mM Tris·HCl (pH 7.5), 1 mM MgCl2, 2 mM DTT, 0.25 M sucrose, 0.03% soybean trypsin inhibitor, 100 µM PMSF, leupeptin (1 µg/ml), and aprotinin (4 µg/ml). Homogenates were centrifuged at 8,000 g for 20 min at 4°C. The supernatants were centrifuged at 100,000 g for 90 min at 4°C, and the resulting microsomal pellet was resuspended in 10 mM Tris·HCl (pH 7.5), 0.15 M KCl, 2 mM DTT, 20 µM CaCl2, and 0.03% soybean trypsin inhibitor.
45Ca2+ uptake assay. 45Ca2+ uptake was determined using the Millipore filtration technique described previously (27). Microsomes (20 µg protein/ml) were incubated at 37°C in a 45Ca2+ uptake medium containing 20 mM MOPS (pH 7.0), 80 mM KCl, 5 mM MgCl2, 5 mM potassium oxalate, and 2 µCi of 45Ca2+ in the absence or presence of 5 mM NaF + 100 nM AlCl3, 5 mM NaF + 50 µM AlCl3, and 10 µM thapsigargin. The reaction was started by addition of 3 mM ATP and terminated at different times by vacuum filtration (0.45-µm Millipore filters). The filters were then washed with 2 mM LaCl3 and 150 mM KCl, and the radioactivity remaining in the filters was determined by scintillation counting.
Values are means ± SE. The statistical significance of differences between averaged data was assessed using the unpaired Student's t-test.
Materials. BSA, MEM amino acids, DMSO, L-glutamine, caffeine, NaF, AlCl3, CCK, EGTA, collagenase (type IV), ATP, PMSF, leupeptin, aprotinin, DTT, soybean trypsin inhibitor, and MOPS were purchased from Sigma (St. Louis, MO); 45Ca2+ from NEN Life Science Products (Boston, MA); and fura 2-acetoxymethyl ester and thapsigargin from Molecular Probes (Eugene, OR).
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RESULTS |
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AlF4--induced [Ca2+]i oscillations were also dependent on the IP3-sensitive Ca2+ store. Because the [Ca2+]i oscillations induced by AlF4- were found to be more dependent on extracellular Ca2+ than those induced by CCK, we next investigated whether AlF4--evoked [Ca2+]i oscillations were independent of the IP3-sensitive intracellular Ca2+ store and mainly generated through Ca2+ channels on the plasma membrane. In rat parotid acinar cells, agonist- and thapsigargin-induced [Ca2+]i oscillations were reported to be generated through CCE channels on the plasma membrane without any involvement of IP3-sensitive Ca2+ channels (5). To test the dependence of AlF4--evoked [Ca2+]i oscillations on IP3-sensitive Ca2+ stores, we first introduced 20 mM caffeine, an inhibitor of IP3 receptors and IP3 production (14, 19), which is known to block the [Ca2+]i oscillations generated through IP3-sensitive Ca2+ channels, but not the [Ca2+]i oscillations generated through Ca2+ channels on the plasma membrane (5). Caffeine at 20 mM completely blocked AlF4--evoked [Ca2+]i oscillations (n = 4; Fig. 2A), suggesting that generation of [Ca2+]i oscillations in response to AlF4- requires Ca2+ release through IP3-sensitive Ca2+ channels. In addition, the oscillations were acutely discontinued after the intracellular Ca2+ store was depleted by 2 µM thapsigargin (n = 4; Fig. 2B). Furthermore, AlF4- induced one to three spikes in Ca2+-free solution, suggesting that [Ca2+]i oscillations can be initiated independently of Ca2+ influx (n = 4; Fig. 2C). These results imply that the IP3-sensitive Ca2+ store is essential for initiation and maintenance of the [Ca2+]i oscillations evoked by AlF4-.
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AlF4- decreased the amount of Ca2+ in the Ca2+ store, probably by inhibiting sarco/endoplasmic reticulum Ca2+ ATPase activity. Because AlF4--evoked [Ca2+]i oscillations were not sustained after perfusate Ca2+ was withdrawn, it can be assumed that the amount of Ca2+ in the store was not sufficient to maintain the oscillations in the absence of a supply of Ca2+ from the extracellular space. Therefore, we measured the size of the Ca2+ store during CCK or AlF4- stimulation by using thapsigargin to measure the amount of Ca2+ released from the store. Accordingly, we changed the perfusate to a Ca2+-free solution containing 2 µM thapsigargin during [Ca2+]i oscillation. During AlF4-stimulation, the amplitude of the [Ca2+]i increase caused by changing the perfusate to 2 µM thapsigargin-containing Ca2+-free solution was 139.3 ± 13.9 nM (n = 4) when the perfusate was changed just after the [Ca2+]i oscillations had been initiated, but this was reduced to 42.2 ± 3.3 nM (n = 4, P < 0.05) when the perfusate was changed after the fourth peak (Fig. 3A, B, and E). In contrast to the marked decrease in peak size during AlF4- stimulation, the amplitudes of the [Ca2+]i increases caused by the perfusate changes were not significantly different during stimulation with 20 pM CCK: 173.5 ± 18.3 nM just after the initiation of the [Ca2+]i oscillations and 178.5 ± 13.1 nM just after the fourth peak (n = 4 each; Fig. 3, C-E).
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Because sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) is the major contributor to the maintenance of Ca2+ concentrations in the store, we examined whether AlF4- inhibits SERCA activity. The SERCA activity on the isolated microsomes may be represented by the rate of 45Ca2+ uptake into the microsomes. Therefore, we measured the 45Ca2+ uptake at 2-min intervals in the absence or presence of AlF4-. The rate of 45Ca2+ uptake was reduced by 23% by pretreatment with 5 mM NaF + 100 nM AlCl3 (n = 8; Fig. 4). In addition, pretreating the microsomes with 5 mM NaF + 50 µM AlCl3 decreased the rate of 45Ca2+ uptake by 58% (n = 8), indicating that AlF4- directly inhibited the Ca2+-ATPase activity dose dependently. AlCl3 (50 µM) in the absence of NaF did not inhibit the 45Ca2+ uptake (n = 3). Thapsigargin (10 µM) reduced Ca2+-ATPase activity by 91% (n = 8), suggesting that the ATPase activity detected in this experiment was mainly SERCA activity.
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Rate of Ca2+ efflux was increased by AlF4- and CCK to a similar extent. We also tested whether the rate of Ca2+ efflux was affected by AlF4-. The rate of Ca2+ efflux was measured by calculating the rate of Ca2+ decline at the same [Ca2+]i after an acute change of perfusate to a 2 µM thapsigargin-containing Ca2+-free solution during AlF4- or CCK stimulation. The rate of Ca2+ efflux was 0.89 ± 0.12 nM/s (n = 8) during stimulation with 20 pM CCK (Fig. 5A) and 0.8 ± 0.18 nM/s (n = 9) during stimulation with AlF4- (Fig. 5B). The efflux rate of Ca2+ was 0.44 ± 0.09 nM/s (n = 5) in the absence of stimulation (Fig. 5C). Therefore, the rate of Ca2+ efflux was higher during AlF4- stimulation than in the absence of stimulation, but it was not significantly different from that observed during CCK stimulation.
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Partial inhibition of SERCA made CCK-evoked [Ca2+]i oscillations more dependent on extracellular Ca2+. To test whether the partial inhibition of SERCA was responsible for dependence of the [Ca2+]i oscillations on extracellular Ca2+, cells were exposed to a low concentration of thapsigargin before the addition of CCK. As shown in Fig. 6, [Ca2+]i increased slightly after addition of 1 nM thapsigargin. Moreover, in the presence of 1 nM thapsigargin, 20 pM CCK induced [Ca2+]i oscillations of lower amplitude (97.2 ± 10.8 nM, n = 11) than those induced by 20 pM CCK alone (149.2 ± 29.3 nM, n = 10, P < 0.05). When Ca2+ was removed from the perfusate, [Ca2+]i oscillations rapidly stopped (n = 11). These results suggest that a reduced Ca2+ loading in the Ca2+ store, due to the partial inhibition of SERCA, may be responsible for the extracellular Ca2+ dependence of [Ca2+]i oscillations in response to AlF4-.
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DISCUSSION |
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We first examined whether AlF4- induced repetitive Ca2+ influx by acting at the plasma membrane. Membrane-linked [Ca2+]i oscillations have been previously reported in guinea pig ileal smooth muscle cells stimulated with AlF4- (7). In this cell type, AlF4- (10 µMAl3+ + 1 mM F-) evoked [Ca2+]i oscillations by causing the periodic opening and closing of voltage-dependent Ca2+ channels in the plasma membrane. AlF4- inhibits plasma membrane Ca2+-ATPase (PMCA), causing membrane depolarization, which leads to the opening of voltage-operated Ca2+ channels. However, in pancreatic acinar cells in which voltage-operated Ca2+ channels are not functional, the mechanism for the generation of [Ca2+]i oscillations does not seem to be the same as that in smooth muscle cells. However, guinea pig ileal smooth muscle cells are not unique in terms of generating "membrane-type [Ca2+]i oscillations." In rat salivary acinar cells, high concentrations of Ca2+-mobilizing agonists or thapsigargin were also shown to generate membrane-type [Ca2+]i oscillations through CCE channels (5). To test whether AlF4--induced [Ca2+]i oscillations originate from the plasma membrane in rat pancreatic acinar cells, we treated cells with caffeine during [Ca2+]i oscillation. High concentrations of caffeine (>10 mM) are known to block IP3 receptors (14, 21) and to inhibit IP3 production in mouse pancreatic acinar cells (19). Therefore, if AlF4- does not require an IP3-sensitive intracellular Ca2+ store to generate [Ca2+]i oscillations and simply acts on the plasma membrane, caffeine should not have an inhibitory effect on the generation of [Ca2+]i oscillations, as shown previously (5). However, 20 mM caffeine immediately blocked AlF4--evoked [Ca2+]i oscillations. In addition, we also found that depletion of the IP3-sensitive Ca2+ store with the use of thapsigargin stopped the [Ca2+]i oscillations. These results indicate that cyclic release of Ca2+ from the IP3-sensitive Ca2+ store is essential for generation of [Ca2+]i oscillations. However, these results do not necessarily mean that Ca2+ influx is not the primary target of AlF4- action. Recent studies have indicated that elevation of [Ca2+]i activates IP3 channel gating in the absence of IP3 (23). If AlF4- activates the Ca2+ influx pathway, this may trigger Ca2+ release from IP3-sensitive Ca2+ stores. To test this possibility, we simply exposed the cells to AlF4- in the absence of perfusate Ca2+ and found that [Ca2+]i oscillations were initiated, even in the absence of Ca2+ influx. Because AlF4- has been known to activate heterotrimeric G proteins by forming a G-GDPAlF4- complex, which resembles G
·GTP, these results imply that the generation of IP3 via activation of Gq/11 proteins and subsequent activation of IP3 receptors play a fundamental role in initiation and maintenance of [Ca2+]i oscillations and that the plasma membrane is not the primary target of AlF4- in terms of generating [Ca2+]i oscillations.
The second possible explanation for the strong dependence of AlF4--induced [Ca2+]i oscillations on Ca2+ influx is that AlF4- may reduce the activity of SERCA and the size of the intracellular Ca2+ store. During [Ca2+]i oscillations induced by CCK in rat pancreatic acinar cells, Ca2+ released from the store is mainly resequestered into the store by SERCA and only partly expelled into the extracellular space by PMCA (20, 22). However, if SERCA activity is reduced, more Ca2+ is pumped out of the cells and the store becomes depleted during [Ca2+]i oscillations. In this case, [Ca2+]i oscillations could be maintained only with the aid of Ca2+ influx through the CCE pathways. Our data indeed showed that the activity of SERCA was directly inhibited by 23% with AlF4- at the concentration we used and that the amount of Ca2+ in the store decreased as the AlF4--induced [Ca2+]i oscillations continued. Therefore, it seems that a 23% reduction in SERCA activity has a profound effect on the reuptake of released Ca2+ by the store; i.e., reuptake of Ca2+ by the store decreases, and thus Ca2+ efflux increases. However, despite the 23% reduction in activity, SERCA may still allow refilling of the stores with Ca2+, probably during the interspike phase, which results in maintenance of [Ca2+]i oscillations. A higher concentration of AlF4- (5 mM NaF + 50 µM AlCl3) inhibited SERCA activity by 58% and induced a tonic increase in [Ca2+]i (data not shown), indicating that the strong inhibition of SERCA with a high concentration of AlF4- causes a rapid depletion of the Ca2+ store and fails to recharge the store.
In contrast to SERCA, our study showed that the rate of Ca2+ efflux, which might represent PMCA activity, was increased by AlF4-. This is in good agreement with a previous report in which it was found that Ca2+-mobilizing hormones activate PMCA activity in rat pancreatic acinar cells by activating protein kinase C (13). In our study, the increased activity of PMCA by CCK stimulation was similar to that achieved by AlF4- stimulation, suggesting that activation of PMCA per se does not play a crucial role in making [Ca2+]i oscillations dependent on extracellular Ca2+. Although it was reported that AlF4- directly inhibits PMCA in pig stomach smooth muscle and erythrocytes (11), the direct effect of AlF4-, at the concentration we used, on PMCA appeared to be minimal in rat pancreatic acinar cells; i.e., no significant difference was observed between the rates of Ca2+ efflux during AlF4- and CCK stimulation, although the Ca2+ efflux rate was slightly lower during AlF4- stimulation than during CCK stimulation.
Having confirmed the inhibition of SERCA by AlF4-, we sought to determine whether the partial inhibition of SERCA was responsible for dependence of the oscillations on extracellular Ca2+. Because thapsigargin is known to inhibit SERCA specifically and dose dependently, we used 1 nM thapsigargin to inhibit SERCA partially. Previously, 0.1-1 nM thapsigargin was reported to inhibit SERCA activity by 20-30% in mouse cardiac tissue homogenates (8). In our system, 1 nM thapsigargin often induced a slight increase in [Ca2+]i, suggesting that this concentration of thapsigargin caused partial inhibition of SERCA. Comparing the amplitude of the spikes evoked by 20 pM CCK in the absence and in the presence of 1 nM thapsigargin, we found that the amplitude of spikes decreased by 35% when thapsigargin was present. A similar observation was made by Petersen and colleagues (15) in mouse pancreatic acinar cells. They reported that partial inhibition of SERCA by 500 pM thapsigargin in mouse pancreatic acinar cells decreased the mean amplitude of IP3-induced [Ca2+]i oscillations by 26%. Our study and that of Petersen and colleagues may imply that the reduced amount of Ca2+ in the stores caused by partial SERCA inhibition results in less Ca2+ release per spike. However, the most striking effect of the partial inhibition of SERCA on CCK-induced [Ca2+]i oscillations was the immediate termination of [Ca2+]i oscillations on withdrawal of the perfusate Ca2+. Partial inhibition of SERCA may decrease the rate of Ca2+ reuptake into the store, and thus Ca2+ would be preferentially pumped out by PMCA. Therefore, if SERCA is partially inhibited, the amount of Ca2+ available in the store for the next spike would be reduced and a greater Ca2+ influx would be needed to recharge the stores to maintain [Ca2+]i oscillations; i.e., [Ca2+]i oscillations become critically dependent on the extracellular Ca2+ by partial inhibition of SERCA.
With consideration that SERCA is a crucial element involved in the regulation of intracellular Ca2+ homeostasis, a decrease in SERCA activity would be expected to cause a profound impairment of Ca2+ signaling. However, in the present study, we showed that [Ca2+]i oscillations were maintained, even in the condition of decreased SERCA activity, and that the maintenance of [Ca2+]i oscillations was attributed to functional compensation by Ca2+ influx. The plasticity of Ca2+ signaling appears to be an important feature to maintain intracellular Ca2+ homeostasis and normal cell functions. In support of this, Zhao and colleagues (26) reported a remarkable plasticity and adaptability of Ca2+ signaling and Ca2+-dependent cellular functions in SERCA2+/- mice. In their study, although the rate of Ca2+ uptake was 50% slower into the internal stores of the permeabilized pancreatic acini from SERCA2+/- mice than into the store of wild-type mice, agonist-stimulated exocytosis was identical in these cell types. Therefore, even if SERCA activity is reduced, normal physiology can be ensured by plasticity of Ca2+ signaling.
In conclusion, the strong dependence of AlF4--induced [Ca2+]i oscillations on Ca2+ influx is probably due to the reduction of the activity of SERCA and the size of the intracellular Ca2+ stores.
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DISCLOSURES |
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FOOTNOTES |
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The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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REFERENCES |
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![]() ![]() ![]() ![]() ![]() ![]() |
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2. Berridge MJ, Lipp P, and Bootman MD. The versatility and universality of calcium signalling. Nat Rev Mol Cell Biol 1: 11-21, 2000.[ISI][Medline]
3. Bigay J, Deterre P, Pfister C, and Chabre M. Fluoride complexes of aluminum or beryllium act on G-proteins as reversibly bound analogues of the -phosphate of GTP. EMBO J 6: 2907-2913, 1987.[Abstract]
4. Clapham DE. Calcium signaling. Cell 80: 259-268, 1995.[ISI][Medline]
5. Foskett JK and Wong DC. [Ca2+]i inhibition of Ca2+ release-activated Ca2+ influx underlies agonist- and thapsigargin-induced [Ca2+]i oscillations in salivary acinar cells. J Biol Chem 269: 31525-31532, 1994.
6. Grynkiewicz G, Poenie M, and Tsien RY. A new generation of Ca2+ indicators with greatly improved fluorescence properties. J Biol Chem 260: 3440-3450, 1985.[Abstract]
7. Himpens B, Missiaen L, Droogmans G, and Casteels R. AlF4- induces Ca2+ oscillations in guinea-pig ileal smooth muscle. Pflügers Arch 417: 645-650, 1991.[ISI][Medline]
8. Ji Y, Loukianov E, and Periasamy M. Analysis of sarcoplasmic reticulum Ca2+ transport and Ca2+ ATPase enzymatic properties using mouse cardiac tissue homogenates. Anal Biochem 269: 236-244, 1999.[ISI][Medline]
9. Machkrill JJ, Challiss RAJ, O'Connell DA, Lai FA, and Nahorski SR. Differential expression and regulation of ryanodine receptor and myo-inositol 1,4,5-trisphosphate receptor Ca2+ release channels in mammalian tissues and cell lines. Biochem J 327: 251-258, 1997.[ISI][Medline]
10. Matozaki T, Goke B, Tsunoda Y, Rodriguez M, Martinez J, and Williams JA. Two functionally distinct cholecystokinin receptors show different modes of action on Ca2+ mobilization and phospholipid hydrolysis in isolated rat pancreatic acini. Studies using a new cholecystokinin analog, JMV-180. J Biol Chem 265: 6247-6254, 1990.
11. Missiaen L, Wuytack F, De Smedt H, Vrolix M, and Casteels R. AlF4- reversibly inhibits "P"-type cation-transport ATPases, possibly by interacting with the phosphate-binding site of the ATPase. Biochem J 253: 827-833, 1988.[ISI][Medline]
12. Moon C, Fraser SP, and Djamgoz MB. G-protein activation, intracellular Ca2+ mobilization and phosphorylation studies of membrane currents induced by AlF4- in Xenopus oocytes. CellSignal 9: 497-504, 1997.[ISI][Medline]
13. Muallem S, Pandol SJ, and Beeker TG. Calcium mobilizing hormones activate the plasma membrane Ca2+ pump of pancreatic acinar cells. J Membr Biol 106: 57-69, 1988.[ISI][Medline]
14. Parker I and Ivorra I. Caffeine inhibits inositol trisphosphate-mediated liberation of intracellular calcium in Xenopus oocytes. J Physiol 433: 229-240, 1991.[Abstract]
15. Petersen CC, Petersen OH, and Berridge MJ. The role of endoplasmic reticulum calcium pumps during cytosolic calcium spiking in pancreatic acinar cells. J Biol Chem 268: 22262-22264, 1993.
16. Putney JW Jr. A model for receptor-regulated calcium entry. Cell Calcium 7: 1-12, 1986.[ISI][Medline]
17. Putney JW Jr, Broad LM, Braun FJ, Lievremont JP, and Bird GS. Mechanisms of capacitative calcium entry. J Cell Sci 114: 2223-2229, 2001.[ISI][Medline]
18. Thomas D, Lipp P, Tovey SC, Berridge MJ, Li W, Tsien RY, and Bootman MD. Microscopic properties of elementary Ca2+ release sites in non-excitable cells. Curr Biol 10: 8-15, 2000.[ISI][Medline]
19. Toescu EC, O'Neill SC, Petersen OH, and Eisner DA. Caffeine inhibits the agonist-evoked cytosolic Ca2+ signal in mouse pancreatic acinar cells by blocking inositol trisphosphate production. J Biol Chem 267: 23467-23470, 1992.
20. Tsunoda Y, Stuenkel EL, and Williams JA. Oscillatory mode of calcium signaling in rat pancreatic acinar cells. Am J Physiol Cell Physiol 258: C147-C155, 1990.
21. Wakui M, Kase H, and Petersen OH. Cytoplasmic Ca2+ signals evoked by activation of cholecystokinin receptors: Ca2+-dependent current recording in internally perfused pancreatic acinar cells. J Membr Biol 124: 179-187, 1991.[ISI][Medline]
22. Williams JA. Intracellular signaling mechanisms activated by cholecystokinin-regulating synthesis and secretion of digestive enzymes in pancreatic acinar cells. Annu Rev Physiol 63: 77-97, 2001.[ISI][Medline]
23. Yang J, McBride S, Mak DO, Vardi N, Palczewski K, Haeseleer F, and Foskett JK. Identification of a family of calcium sensors as protein ligands of inositol trisphosphate receptor Ca2+ release channels. Proc Natl Acad Sci USA 99: 7711-7716, 2002.
24. Yule DI, Lawrie AM, and Gallacher DV. Acetylcholine and cholecystokinin induce different patterns of oscillating calcium signals in pancreatic acinar cells. Cell Calcium 12: 145-151, 1991.[ISI][Medline]
25. Yule DI and Williams JA. Mastoparan induces oscillations of cytosolic Ca2+ in rat pancreatic acinar cells. Biochem Biophys Res Commun 177: 159-165, 1991.[ISI][Medline]
26. Zhao XS, Shin DM, Liu LH, Shull GE, and Muallem S. Plasticity and adaptation of Ca2+ signaling and Ca2+-dependent exocytosis in SERCA2+/- mice. EMBO J 20: 2680-2689, 2001.
27. Zhong L and Inesi G. Role of the S3 stalk segment in the thapsigargin concentration dependence of sarco-endoplasmic reticulum Ca2+ ATPase inhibition. J Biol Chem 273: 12994-12998, 1998.
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