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Am J Physiol Cell Physiol 271: C242-C247, 1996;
0363-6143/96 $5.00
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AJP - Cell Physiology, Vol 271, Issue 1 C242-C247, Copyright © 1996 by American Physiological Society

ARTICLES

Inhibition of renin secretion by Ca2+ through activation of myosin light chain kinase

C. S. Park, S. H. Chang, H. S. Lee, S. H. Kim, J. W. Chang and C. D. Hong
Department of Physiology, University of Ulsan College of Medicine, Seoul, Korea.

This study sought to identify specific enzyme(s) involved in the biochemical cascade of inhibition of renin secretion through Ca(2+)-calmodulin mediation with the use of inhibitors of protein kinase and phosphatases. Inhibition of renin secretion mediated by Ca(2+)-calmodulin was induced by incubating rat renal cortical slices in K(+)-rich depolarizing medium, producing > 50% inhibition. This inhibition was completely blocked by the calmodulin antagonist calmidazolium. The inhibitor of protein kinase with broad specificity, K-252a, blocked the inhibition of renin secretion. Neither KN-62, a specific inhibitor of Ca(2+)-calmodulin-dependent protein kinase II (CaMK II), nor specific inhibitors of protein phosphatase 2B (PP2B), cyclosporin A and FK-506, blocked the inhibition. On the other hand, all four known inhibitors specific for myosin light chain kinase (MLCK), with different chemical structures and mechanisms of inhibition (ML-9, ML-7, KT-5926 and wortmannin), almost completely protected renin secretion against the inhibition by Ca2+. In particular, ML-9 reversively protected > 77% secretion against the inhibition both in K(+)-rich medium alone and in combination with the calcium ionophore A-23187 in a concentration-dependent manner. Together, these findings from our present study provide the first evidence, albeit indirect in nature, for the possibility that activation of Ca(2+)-calmodulin-dependent MLCK at the downstream of Ca2+ influx into juxtaglomerular (JG) cells leads to phosphorylation of 20-kDa regulatory myosin light chain (MLC20). Through interaction with actin, the phosphorylated MLC20 may play an important role in the inhibitory stimulus-secretion coupling of renin.


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C. S. Park, M. H. Kim, C. H. Leem, Y. J. Jang, H. W. Kim, H. S. Kim, and Y. S. Hong
Inhibitory effect of calyculin A, a Ser/Thr protein phosphatase type I inhibitor, on renin secretion
Am J Physiol Renal Physiol, November 1, 1998; 275(5): F664 - F670.
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M. H. Kim, S.-H. Kim, H. S. Kim, J. W. Chang, Y. S. Hong, H. W. Kim, and C. S. Park
Regulation of Renin Secretion Through Reversible Phosphorylation of Myosin by Myosin Light Chain Kinase and Protein Phosphatase Type 1
J. Pharmacol. Exp. Ther., June 1, 1998; 285(3): 968 - 974.
[Abstract] [Full Text]


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