* Department of Environmental Health and Toxicology, Department of Biomedical Sciences, School of Public Health, University at Albany, Rensselaer, New York 12144;
Wadsworth Center for Laboratories and Research, New York State Department of Health, Albany, New York 12201; and
Institute for Health and the Environment, University at Albany, Rensselaer New York 12144
Received November 19, 2003; accepted February 20, 2004
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Key Words: membrane fluidity; fluorescence polarization; lipid bilayer membranes; thymocytes; cerebellar granule cells.
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Although most health effects of PCBs have been ascribed to the dioxin-like, coplanar congeners, there is abundant evidence from cellular and animal studies that the ortho-substituted, nondioxin-like congeners have biological effects in a great variety of organ systems (Hansen, 1999). In the nervous system ortho-substituted PCBs have been reported to reduce synthesis of the neurotransmitter dopamine (Seegal et al., 1997
), block long-term potentiation, an event thought to be related to learning (Hussain et al., 2000
), cause aberrations in behavior and deficits in memory and learning in rats (Eriksson and Fredriksson, 1996
; Holene et al., 1998
), inhibit adenosine triphosphatases (Maier et al., 1994
), and cause death of cerebellar granule cells (Carpenter et al., 1997
; Kodavanti et al., 1993
; Tan et al., 2004
). Mariussen and Fonnum (2001)
have reported that ortho-substituted, but not coplanar, congeners inhibit uptake of several different neurotransmitters (dopamine, glutamate, GABA, and serotonin) into brain synaptosomes. Ortho-substituted (but not coplanar) PCBs trigger release of insulin from RINm5F cells (Fischer et al., 1999
), stimulate generation of superoxide anion in neutrophils (Ganey et al., 1993
) and stimulate contraction of pregnant rat uterine muscle (Loch-Caruso, 2002
). PCB 153, a di-ortho persistent congener, causes reproductive failure in mink (Patnode and Curtis, 1994
), and interferes with sex hormone regulated processes (Bonefeld-Jorgensen et al., 2001
). Some, but not all, ortho-substituted congeners alter thyroid structure and reduce levels of thyroxine in rats (Ness et al., 1993
). A statistically significant relationship between PCB 153 levels and free testosterone levels and sperm motility has been found in humans (Richthoff et al., 2003
).
The mechanism(s) whereby noncoplanar PCB congeners act has been a matter of debate. The thyroid endocrine disruptive effects are probably mediated by binding of the PCBs to either thyroid hormone receptors or binding proteins and to the induction of glutathione-S-transferase in the liver, resulting in more rapid clearing of thyroid hormone from the blood (Brouwer et al., 1998; Porterfield, 2000
). The sex hormone effects are believed to result from agonist actions of the parent PCB or their hydroxylated metabolites at estrogen receptors (Korach et al., 1988
). The mechanism for reduction of dopamine levels in neurons is believed to be inhibition of the rate-limiting enzyme in dopamine synthesis, tyrosine hydoxylase (Seegal et al., 1997
). Many of the other actions are associated with elevations of intracellular calcium concentration, either from entry across the plasma membrane or secondary to release from intracellular calcium stores. This has been proposed as the mechanism for the release of insulin from RINm5F cells (Fischer et al., 1999
) and the contraction of uterine muscle (Bae et al., 1999
).
Three different hypotheses have been presented to explain at least some of the actions of ortho-substituted PCB congeners. Nishihara and colleagues (Nishihara, 1984; Nishihara et al., 1982
, 1985
; Nishihara and Utsumi, 1986
) studied effects of PCBs on isolated mitochondria. They found that ortho-substituted congeners altered calcium homeostasis by inducing changes in mitochondrial membrane integrity, resulting in loss of mitochondrial membrane potential, ATP generation and swelling with increased permeability to large molecules such as NADH and glucose. Kodavanti and colleagues (Kodavanti et al., 1993
, 1994
, 1996
; Shafer et al., 1996
; Tilson and Kodavanti, 1998
; Kodavanti and Ward, 1998
) have studied cerebellar granule cell neurons, where they have demonstrated a variety of effects of ortho-substituted congeners that are not induced by coplanar PCBs. These include inhibition of microsomal and mitochondrial Ca2+ sequestration, effects on phosphoinositide hydrolysis, protein kinase C activity, and cytotoxicity leading to cell death. More recently they have demonstrated that lower chlorinated, di-ortho-substituted congeners inhibit nitric oxide synthases (Sharma and Kodavanti, 2002
). The central hypothesis from these investigators is that ortho-substituted PCBs alter calcium homeostasis and intracellular second messengers in both mitochondria and endoplasmic reticulum. Pessah and collaborators (Wong and Pessah, 1996
, 1997
; Wong et al., 1997
, 2001
) have also focused on the effects of ortho-substituted PCBs on calcium regulation, but have presented evidence from skeletal and cardiac muscle as well as from neurons that a critical site of action is the ryanodine receptor, which controls a calcium release channel in the endoplasmic reticulum. Their studies have been primarily with PCB 95, which activates ryanodine receptors via an immunophilin-dependent mechanism, leading to a depletion of the endoplasmic reticulum calcium store. The central hypothesis from this group is that the ryanodine receptor is the major target of ortho-substituted congeners.
Our studies on acutely dissociated cerebellar granule cells (Carpenter et al., 1997; Tan et al., 2004
) and thymocytes (Tan et al., 2003
) using flow cytometry have demonstrated that ortho-substituted PCB congeners cause a rapid cell death in both cell types. While the PCB action is accompanied by elevations of intracellular calcium, our evidence indicates that the rise in intracellular calcium is not the cause of the cell death. We also have evidence implicating both mitochondrial and endoplasmic reticulum changes in responses of both cerebellar granule cell neurons and thymocytes to ortho-substituted PCBs. The present studies were designed to test the hypothesis that these congeners exert a relatively nonspecific alteration of all cell membranes.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
A Perkin-Elmer MPF fluorescence spectrophotometer was used to measure steady-state fluorescence polarizations, following the protocol of Lasner et al. (1995). The fluorescence probe, 1,6-diphenyl-1,4,5-hexatriene (DPH), was incorporated into the hydrocarbon chains of the cell membrane lipids (Pap et al., 1994
) as described by Wang and Chen (1993)
and Chen et al. (1998)
. By monitoring the changes in DPH fluorescence polarization, one can investigate the effects of lipophilic agents on membrane fluidity. DPH was initially prepared as a stock solution in tetrahydrofuran at concentrations between 107 and 105 M. A small amount of the DPH solution was then added to thymocytes or cerebellar granule cell neurons. DPH-containing thymocytes or cerebellar granule cell neurons were incubated for 3060 min at room temperature before the addition of an appropriate concentration of the PCB. Steady-state fluorescence polarization was monitored in the absence and presence of PCBs at a time and concentration showing a membrane integrity change and calcium increase, but no obvious cell death.
The effects of PCBs on lipid bilayer vesicles prepared from synthetic L-3-dipalmitoyl phosphatidyl choline (DPPC) were also investigated. The procedures for preparing lipid bilayer vesicles from synthetic DPPC have been described previously (Chen et al., 1996). In brief, DPPC (5 mg in 2 ml distilled water) in a flask filled with nitrogen gas was sonicated, using a sonicator (Brason 2210) with a power output of 50W, at 5°C above the transition temperature of DPPC (42°C) for about 30 min. A small amount of DPH solution was then added to the lipid bilayer vesicles. DPH-containing lipid bilayer vesicles with a molar ratio of DPPH to lipid of 1/500 were then incubated for 3060 min at room temperature, before adding an appropriate concentration of one or the other PCB.
Steady-state fluorescence polarization (P) was measured at room temperature, where the excitation wavelength was at 360 nm and the emission wavelength at 430 nm. The value of P was calculated according to P = (Ivv gIvh)/(Ivv + gIvh), where g is a grating correction factor which is equal to Ihv/Ihh, I is the intensity of the light, v and h denote the vertical and horizontal orientation of the polarizers, and the first and the second subscripts refer to the excitation and emission light, respectively.
The statistical tests used varied with the experiment. Two-way ANOVA was used in experiments such as those shown in Figure 1. A one-way ANOVA (linear regression) was performed on the data in Figure 2, and multiple comparisons tests were applied to the bar graph figures. The Student's t-test was performed for the simple paired tests, with the level p < 0.05 considered to be significant.
|
|
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Figure 2 is a plot of Fluo-3 fluorescence against the PI fluorescence in these cells that are presumed to be injured. The slow accumulation of small amounts of PI in the cells is accompanied by an increase in intracellular calcium concentration, as reflected by Fluo-3 fluorescence. Thus these observations provide evidence that ortho-substituted PCB congeners alter plasma membrane permeability.
Figures 3 and 4 show the effects of exposure to two PCB congeners of equal molecular weight on steady-state DPH fluorescence polarization in cerebellar granule cells and thymocytes, respectively. The PCBs were at a concentration of 2 µM in the granule cells, and at 0.5 µM in the thymocytes. These concentrations were chosen because they are about the threshold concentrations of PCB 52 for clear effects on the accumulation of DNA binding dyes and elevations in intracellular calcium in these two cell types after a 15-min exposure. In both cell types the fluorescence polarization decreased significantly upon incubation with PCB 52, whereas it was unchanged in presence of a similar concentration of the coplanar congener, PCB 77.
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
There is precedent for this hypothesis. As discussed above, Nishihara and colleagues proposed disruption of mitochondrial membranes by ortho-substituted PCBs as long ago as 1982. Lopez-Aparicio et al. (1997) have reported on studies on rat renal tubular cell cultures exposed to PCBs. They found that Aroclor 1248 caused a dose-dependent increase in membrane fluidity. They also studied two PCB congeners, and found that an increase in fluidity was induced by PCB 153, but not by PCB 77. These observations are consistent with our hypothesis. It is interesting that drugs such as cyclosporin A, which rapidly partitions into membranes, is known to cause significant changes in membrane structure, including a change in lipid domain morphology (Soderlund et al., 1999
). Cyclosporin A, which is known to block the mitochondrial permeability transition channel, was found to be the most effective of all agents tested in preventing loss of cell viability in thymocytes (Tan et al., 2003
).
Disruption of the membrane structure can cause changes in ion permeabilities through voltage- or ligand-gated channels, as well as changes in activity of membrane bound enzymes. Disruption of membrane structure can occur at any membrane, whether the plasma membrane or membranes of intracellular organelles such as mitochondria or endoplasmic reticulum, and if such disruption of structure occurs one would expect altered function. We are certainly not proposing that all effects of ortho-substituted congeners are necessarily mediated by this mechanism, but it is likely that some of those involving elevations in intracellular calcium and activation or inhibition of membrane-bound enzymes and second messengers may be.
Our studies of fluorescence steady-state polarization have been done with two PCB congeners of the same molecular weight and the same number of chlorines, but with the chlorines at different positions around the biphenyl ring. Because the chlorine atoms are relatively bulky, when there are chlorines in the ortho positions close to the biphenyl bond on each side they cause the angle between the biphenyl rings to increase, whereas with the chlorines in the meta and para positions, the molecule assumes a planar configuration. There is no reason to assume that the ortho-substituted and coplanar congeners differ greatly in their ability to dissolve in biological membranes, but our observations suggest that the bulky, three dimensional structure of the ortho-substituted congeners causes sufficient perturbation of the membrane lipids so as to cause changes in physiologic function. The physiologic changes that then occur will obviously be dependent upon the specific proteins in different cell membranes. These will be different in neurons as compared to thymocytes, and different yet in other types of cells.
Our results suggest that low or submicromolar concentrations of some ortho-substituted PCBs alter membrane structure, and indicate that this is accompanied by an increase in membrane fluidity as well as accompanying disruption of plasma, mitochondrial and endoplasmic reticulum membrane functions. This may be the mechanism whereby ortho-substituted PCBs alter the function of a variety of cells. The fact that not all cell types are affected similarly or at the same concentration may reflect differences in lipid composition and membrane proteins.
![]() |
NOTES |
---|
1 To whom correspondence should be addressed at School of Public Health, University at Albany, One University Place, B242, Rensselaer, NY 12144. Fax: (518) 525-2665. E-mail: carpent{at}uamail.albany.edu.
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Bonefeld-Jorgensen, E. C., Andersen, H. R., Rasmussen, T. H., and Vinggaard, A. M. (2001). Effect of highly bioaccumulated polychlorinated biphenyl congeners on estrogen and androgen receptor activity. Toxicology 158, 141153.[CrossRef][ISI][Medline]
Brouwer, A., Morse, D. C., Lans, M. C., Schuur, A. G., Murk, A. J., Klasson-Wehler, E., Bergman, A., and Visser, T. J. (1998). Interactions of persistent environmental organohalogens with the thyroid hormone system: Mechanisms and possible consequences for animal and human health. Toxicol. Indust. Health 14, 5984.[ISI][Medline]
Carpenter, D. O., Stoner, C. R. T., and Lawrence, D. A. (1997). Flow cytometric measurements of neuronal death triggered by PCBs. NeuroToxicology 18, 507514.[ISI][Medline]
Chen, C. H., Hoye, K., and Roth, L. G. (1996). Thermodynamic and fluorescence studies of the underlying factors in benzyl alcohol-induced lipid interdigitated phase. Arch. Biochem. Biophys. 333, 401406.[CrossRef][ISI][Medline]
Chen, C. H., Zuklie, B. M., and Roth, L. G. (1998). Elucidation of biphasic alterations on acetycholinesterase (AChE) activity and membrane fluidity in the structure-functional effects of tetracaine on AChE-associated membrane vesicles. Arch. Biochem. Biophys. 351, 135140.[CrossRef][ISI][Medline]
Eriksson, P., and Fredriksson, A. (1996). Developmental neurotoxicity of four ortho-substituted polychlorinated biphenyls in the neonatal mouse. Environ. Toxicol. Pharmacol. 1, 155165.[CrossRef][ISI]
Fischer, L. J., Wagner, M. A., and Madhukar, B. V. (1999). Potential involvement of calcium, CaM Kinase II and MAP kinases in PCB-stimulated insulin release from RINm5F cells. Toxicol. Appl. Pharmacol. 159, 194203.[CrossRef][ISI][Medline]
Ganey, P. E., Sirois, J. E., Denison, M., Robinson, J. P., and Roth, R. A. (1993). Neutrophil function after exposure to polychlorinated biphenyls in vitro. Environ. Health Perspect. 101, 430434.[ISI][Medline]
Hansen, L. G. (1999). The Ortho Side of PCBs: Occurrence and Disposition. Kluwer Academic Publishers, Boston, MA.
Holene, E., Nafstad, I., Skaare, J. U., and Sagvolden, T. (1998). Behavioral hyperactivity in rats following postnatal exposure to sub-toxic doses of polychlorinated biphenyl congeners 153 and 126. Behav. Brain Res. 94, 213224.[CrossRef][ISI][Medline]
Hussain, R. J., Gyori, J., DeCaprio, A. P. and Carpenter, D. O. (2000). In vivo and in vitro exposure to PCB 153 reduces long-term potentiation. Environ. Health Perspect. 108, 827831.[ISI][Medline]
Kodavanti, P. R. S., Shafer, T. J., Ward, T. R., Mundy, W. R., Freudenrich, T., Harry, G. J., and Tilson, H. A. (1994). Differential effects of polychlorinated biphenyl congeners on phosphoinositide hydrolysis and protein kinase C translocation in rat cerebellar granule cells. Brain Res. 662, 7582.[CrossRef][ISI][Medline]
Kodavanti, P. R. S., Shin, D. S., Tilson, H. A., and Harry, G. J. (1993). Comparative effects of two polychlorinated biphenyl congeners on calcium homeostasis in rat cerebellar granule cells. Toxicol. Appl. Pharmacol. 123, 97106.[CrossRef][ISI][Medline]
Kodavanti, P. R. S., and Ward, T. R. (1998). Interactive effects of environmentally relevant polychlorinated biphenyls and dioxins on [3H]phorbol ester binding in rat cerebellar granule cells. Environ. Health Perspect. 106, 479486.[ISI][Medline]
Kodavanti, P. R. S., Ward, T. R., McKinney, J. D., and Tilson, H. A. (1996). Inhibition of microsomal and mitochondrial Ca2+-sequestration in rat cerebellum by polychlorinated biphenyl mixtures and congeners. Structure-activity relationships. Arch. Toxicol. 70, 150157.[CrossRef][ISI][Medline]
Korach, K. S., Sarver, P., Chae, K., McLachlan, J. A., and McKinney, J.D . (1988). Estrogen receptor binding of polychlorinated hydroxybiphenyls: Conformationally restricted structural probes. Mol. Pharmacol. 33, 120126.[Abstract]
Lasner, M., Roth, L. G., and Chen, C. H. (1995). Structure-functional effects of a series of alcohols on acetylcholinesterase-associated membrane vesicles: Elucidation of factors contributing to the alcohol action. Arch. Biochem. Biophys. 317, 391396.[CrossRef][ISI][Medline]
Loch-Caruso, R. (2002). Uterine muscle as a potential target of polychlorinated biphenyls during pregnancy. Int. J. Hyg. Environ. Health 205, 121130.[ISI][Medline]
Lopez-Aparicio, P., Merino, M. J., Sanchez, E., Recio, M. N., and Perez-Albarsanz, M. A. (1997). Effect of Aroclor 1248 and two pure PCB congeners upon the membrane fluidity of rat renal tubular cell cultures. Pestic. Biochem. Physiol. 57, 5462.[CrossRef][ISI]
Maier, W. E., Kodavanti, P. R. S., Harry, G. J., and Tilson, H. A. (1994). Sensitivity of adenosine triphosphatase in different brain regions to polychlorinated biphenyl congeners. J. Appl. Toxicol. 14, 225229.[ISI][Medline]
Mariussen, E., and Fonnum, F. (2001). The effect of polychlorinated bipyhenyls on the high affinity uptake of the neurotransmitters dopamine, serotonin, glutamate and GABA into rat brain synaptosomes. Toxicology 159, 1121.[CrossRef][ISI][Medline]
Ness, D. K., Schantz, S. L., Moshtaghian, J., and Hansen, L. G. (1993). Effects of perinatal exposure to specific PCB congeners on thyroid hormone concentrations and thyroid histology in the rat. Toxicol. Letts. 68, 311323.[CrossRef][ISI][Medline]
Nishihara, Y. (1984). Uncoupling action of polychlorinated bipyhenyls (Kanechlor-400) on oxidative phosphorylation in rat liver mitochondria. Arch. Environ. Contam. Toxicol. 13, 225229.[ISI][Medline]
Nishihara, Y., Iwata, M., Ikawa, K., Puttmann, M., Robertson, L.W., Miyahara, M., Terada, H., and Utsumi, K. (1982). The influence of chlor-substituent sites of hexachlorobiphenyl on the respiration of rat liver mitochondria. Chem. Pharm. Bull. (Tokyo) 40, 27692774.
Nishihara, Y., Robertson, L. W., Oesch, F., and Utsumi, K. (1985). Interaction of tetrachlorobiphenyls with isolated rat liver mitochondria. J. Pharmacobiodyn. 8, 726732.[Medline]
Nishihara, Y., and Utsumi, K. (1986). 2,5,2',5'-tetrachlorobiphenyl impairs the bioenergetic functions of isolated rat liver mitochondria. Biochem. Pharmacol. 35, 33353339.[CrossRef][ISI][Medline]
Pap, E. H., ter Horst, J. J., van Hoek, A., and Visser, A. J. (1994). Fluorescence dynamics of diphenyl-1,3,5-hexatriene-labelled phospholipids in bilayer membranes. Biophys. Chem. 48, 337351.[CrossRef][ISI][Medline]
Patnode, K. A., and Curtis, L. R. (1994). 2,2',4,4',5,5'- and 3,3',4,4',5,5'-hexachlorobiphenyl alteration of uterine progesterone and estrogen receptors coincides with embryotoxicity in mink (Mustela vision). Toxicol. Appl. Pharmacol. 172, 918.
Porterfield, S. P. (2000). Thyroidal dysfunction and environmental chemicalspotential impact on brain development. Environ. Health Perspect. 108(Suppl. 3), 433438.[ISI][Medline]
Raff, M. C., and De Petris, S. (1973). Movement of lymphocyte surface antigens and receptors: The fluid nature of the lymphocyte plasma membrane and its immunological significance. Fed. Proc. 32, 4854.[ISI][Medline]
Richthoff, J., Rylander, L., Jonsson, B. A., Akesson, H., Hagmar, L., Nilsson-Ehle, P., Stridsberg, M., and Giwercman, A. (2003). Serum levels of 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) in relation to markers of reproductive function in young males from the general Swedish population. Environ. Health Perspect. 111, 409413.[ISI][Medline]
Seegal, R. F., Brosch, K. O., and Okoniewski, R. J. (1997). Effects of in utero and lactational exposure of the laboratory rat to 2,4,2',4'- and 3,4,3',4'-tetrachlorobiphenyl on dopamine function. Toxicol. Appl. Pharmacol. 146, 95103.[CrossRef][ISI][Medline]
Shafer, T. J., Munday, W. R., Tilson, H. A., and Kodavanti, P. R. S. (1996). Disruption of inositol phosphate accumulation in cerebellar granule cells by polychlorinated biphenyls: A consequence of altered Ca2+ homeostasis. Toxicol. Appl. Pharmacol. 141, 448455.[CrossRef][ISI][Medline]
Sharma, R., and Kodavanti, P. R. S. (2002). In vitro effects of polychlorinated biphenyls and hydroxy metabolities on nitric oxide synthases in rat brain. Toxicol. Appl. Pharmacol. 178, 127136.[CrossRef][ISI][Medline]
Silensky, M. (1974). Homeoviscous adaptationa homeostatic process that regulates the viscosity of membrane lipids in Escherichia coli. Proc. Natl. Acad. Sci. 71, 522525.[Abstract]
Singer, S. J., and Nicolson, G. L. (1972). The fluid mosaic model of the structure of cell membranes. Science 175, 720732.[ISI][Medline]
Soderlund, T., Lehtonen, J. Y. A., and Kinnunen, P. K. J. (1999). Interactions of cyclosporin A with phospholipid membranes: Effect of cholesterol. Mol. Pharmacol. 55, 3238.
Steck, T. L. (1974). The organization of proteins in the human red blood cell membrane. J. Cell. Biol. 62, 119.
Tan, Y., Li, D., Song, R., Lawrence, D., and Carpenter, D. O. (2003). Ortho-substituted PCBs kill thymocytes. Toxicol. Sci. 76, 328337.
Tan, Y., Song, R., Lawrence, D., and Carpenter, D.O. (2004). Ortho-substituted but not coplanar PCBs rapidly kill cerebellar granule cells. Toxicol. Sci. (in press).
Tilson, H. A., and Kodavanti, P. R. S. (1998). The neurotoxicity of polychlorinated biphenyls. NeuroToxicology 19, 517526.[ISI][Medline]
Wang, G., and Chen, C. H. (1993). Thermodynamic elucidation of structural stability of deuterated biological molecules: Deuterated phospholipid vesicles in H2O. Arch. Biochem. Biophys. 301, 330335.[CrossRef][ISI][Medline]
Woodson, P. B. J., Traynor, M. E., Schlapfer, W. T., and Barondes, S. H. (1976). Increased membrane fluidity implicated in acceleration of decay of post-tetanic potentiation by alcohols. Nature 260, 797799.[ISI][Medline]
Wong, P. W., Garcia, E. F., and Pessah, I. N. (2001). Ortho-Substitued PCB95 alters intracellular calcium signaling and causes cellular acidification in PC12 cells by an immunophilin-dependent mechanism. J. Neurochem. 76, 450463.[CrossRef][ISI][Medline]
Wong, P. W., Joy, R. M., Albertson, T. E., Schantz, S. L., and Pessah, I. N. (1997). Ortho-substituted 2,2',3,5',6-pentachlorobiphenyl (PCB95) alters rat hippocampal ryanodine receptors and neuroplasticity in vitro: Evidence for altered hippocampal function. NeuroToxicology 18, 443345.[ISI][Medline]
Wong, P. W., and Pessah, I. N. (1996). Ortho-substituted polychlorinated biphenyls alter calcium regulation by a ryanodine receptor-mediated mechanism: Structural specificity toward skeletal- and cardiac-type microsomal calcium release channels. Mol. Pharmacol. 49, 740751.[Abstract]
Wong, P. W., and Pessah, I. N. (1997). Noncoplanar PCB 95 alters microsomal calcium transport by an immunophilin FKBP12-dependent mechanism. Mol. Pharmacol. 51, 693702.