Ca(2+)-dependent kinase and phosphatase control inositol 1,4,5-trisphosphate-mediated Ca2+ release. Modification by agonist stimulation.
A permeable cell system in which Ca2+ release can be evoked by inositol 1,4,5-trisphosphate (IP3) or agonist stimulation was used to study the regulation of Ca2+ release by Ca2+ itself. At low concentrations, Ca2+ activated IP3-mediated Ca2+ release (IMCR) with half-maximal effect at about 15 nM. At high concentrations, Ca2+ inhibited IMCR giving rise to a biphasic [Ca2+] dependence of IMCR. The activation of IMCR by Ca2+ appears to be mediated by a kinase, probably the Ca(2+)-and calmodulin-dependent protein kinase (CaMKII). Thus, the activation required MgATP, completely blocked at 0 degrees C, required Ca2+, and was inhibited by the CaMKII inhibitors KT5926 and KN62. The inhibition of IMCR seems to be mediated by a protein phosphatase, probably the Ca(2+)-dependent protein phosphatase 2B. Hence, the inhibition required Ca2+, was prevented by the general protein phosphatase inhibitor pyrophosphate and by the immunosuppressants cyclosporin A and FK506, but not by okadaic acid or VO4(2-), and was modified by chelating agents such as EGTA. Stimulation with agonists modified the activities of the kinase and phosphatase to make the release independent of [Ca2+]. This appears to be due to an increase in the apparent affinity for Ca2+ in stimulating IMCR and inhibition of the phosphatase. We suggest that agonist-dependent modification of the kinase/phosphatase activity ratio can be the biochemical pathway responsible for regulation of Ca2+ release and in turn [Ca2+]i oscillations.
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235-9040.
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Zhang
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Zhao
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Muallem
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002460:Cell Line; D004533:Egtazic Acid / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*
D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004533:Egtazic Acid; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D010749:Phosphoprotein Phosphatases; D008274:Magnesium; D002118:Calcium