AJP - Cell Physiology, Vol 259, Issue 5 C769-C774, Copyright © 1990 by American Physiological Society

ARTICLES

Alteration in the myosin phosphorylation pattern of smooth muscle by phorbol ester

M. Seto, Y. Sasaki and Y. Sasaki
Biochemical Research Laboratory, Asahi Chemical Industry, Miyazaki, Japan.

Pretreatment with a high concentration of phorbol 12-myristate 13-acetate (PMA, 100 nM) increased the degree of tension and extent of myosin light chain (MLC20) phosphorylation in the K(+)-stimulated rabbit aortic artery. Pretreatment with 100 nM PMA did not alter the relationship between MLC20 phosphorylation and the tension seen with K+ stimulation in the initial phase and steady state of contraction. However, a low concentration of PMA (10 nM) potentiated only the MLC20 phosphorylation during the steady state of contraction with no effect on the tension. In contrast, the prostaglandin (PG) F2 alpha-induced tension development and the MLC20 phosphorylation were not affected by PMA pretreatment at both low and high concentrations. The inhibitory action of nifedipine on the K(+)-induced contraction was not affected by pretreatment with 100 nM PMA; the concentration producing half-maximal inhibition of nifedipine for the K(+)-induced contraction (33 nM) was the same as that of the K+ plus 100 nM PMA-induced contraction (32 nM). Our results suggest that PMA may increase the level of myosin light chain kinase-dependent MLC20 phosphorylation and the tension in the K(+)-stimulated artery, an effect which differs from that seen with increases in K+ concentrations. The regulatory mechanism for the contraction involving PGF2 alpha stimulation may differ from that seen in the case of K+ stimulation.

This article has been cited by other articles:

				K. Sakurada, M. Seto, and Y. Sasaki Dynamics of myosin light chain phosphorylation at Ser19 and Thr18/Ser19 in smooth muscle cells in culture Am J Physiol Cell Physiol, June 1, 1998; 274(6): C1563 - C1572. [Abstract] [Full Text] [PDF]

				N. Katsumata, H. Shimokawa, M. Seto, T. Kozai, T. Yamawaki, K. Kuwata, K. Egashira, I. Ikegaki, T. Asano, Y. Sasaki, et al. Enhanced Myosin Light Chain Phosphorylations as a Central Mechanism for Coronary Artery Spasm in a Swine Model With Interleukin-1ß Circulation, December 16, 1997; 96(12): 4357 - 4363. [Abstract] [Full Text]