Pharmacological differentiation between intracellular calcium pump isoforms
Engelender, S.; De Meis, L.
Molecular Pharmacology 50(5): 1243-1252
1996
ISSN/ISBN: 0026-895X PMID: 8913356 Document Number: 465267
We studied the Ca-2+-ATPase isoforms of sarco/endoplasmic reticulum (SERCA) derived from cerebellum, cardiac muscle, and skeletal muscle. The Mg-2+ dependence varied among the three enzyme preparations. The Ca-2+ transport in skeletal muscle vesicles, but not in cerebellar or cardiac vesicles, was activated by free Mg-2+ concentrations varying from 0.1 to 0.3 mM. Concentrations of Mg-2+ of gt 1 mM inhibited Ca-2+ transport in all three vesicle preparations but with more pronounced effect in cerebellar and cardiac vesicles. At 10-80 mu-M, trifluoperazine activated Ca-2+ uptake in cerebellar and cardiac vesicles but not in skeletal muscle vesicles. The activation was due to an increase in the coupling ratio between Ca-2+ transport and ATP hydrolysis and was observed only in the presence of ATP concentrations of gt 100 mu-M. The Ca-2+ transport in all three vesicle preparations was inhibited by trifluoperazine concentrations of gt 100 mu-M. The inhibition promoted by trifluoperazine was prevented by the addition of dimethylsulfoxide (10% v/v) to the medium. The Ca-2+ efflux from loaded vesicles was increased by arsenate and even more by trifluoperazine. In skeletal muscle vesicles, the efflux promoted by arsenate was several-fold faster than that promoted in vesicles derived from cerebellum or cardiac muscle. In skeletal muscle, the enhancement of Ca-2+ efflux promoted by both arsenate and trifluoperazine was antagonized by thapsigargin, Ca-2+, Mg-2+ , and K+. These agents partly antagonized the enhancement of Ca-2+ efflux promoted by trifluoperazine in cardiac vesicles but had little or no effect in the cerebellar vesicles. Finally, Mg cntdot P-i and Mg cntdot ATP, the two substrates that phosphorylate the Ca-2+ATPase, antagonized the effect of trifluoperazine in all of the preparations tested. The concentration of ATP needed was in the same range as that of the second K-m value for ATP (50-300 mu-M) of the SERCA isoforms. The results indicate that the effect of the drugs on the cytosolic Ca-2+ homeostasis may vary depending on the target tissue.