Myosin light chain phosphorylation in human myometrial smooth muscle cells

Abstract

Ca2+/calmodulin-dependent phosphorylation of the 20-kDa regulatory light chain of myosin is of signal importance in the initiation of contraction in a number of smooth muscle tissues. In this investigation, we evaluated the relationship between intracellular free Ca2+/concentration [( Ca2+]i) and the extent of myosin light chain phosphorylation in cultured human myometrial smooth muscle cells. Treatment of myometrial cells with ionomycin caused a concentration- and time-dependent increase in [Ca2+]i and phosphorylation of myosin light chain. Temporally, the increases in light chain phosphorylation and [Ca2+]i in response to ionomycin were similar. In myometrial cells treated with ionomycin (10(-5) M) for 10 s, [Ca2+]i increased from 138 to 800 nM; in these same cells, myosin light chain phosphorylation increased from 5% to a maximum value of 54%. Half-maximal phosphorylation of myosin light chain was attained at 300 nM [Ca2+]i. Treatment of myometrial smooth muscle cells with prostaglandin (PG) F2 alpha (10(-8) M) and PGE2 (10(-8) M) caused a proportionate increase in [Ca2+]i and myosin light chain phosphorylation. In addition, [Ca2+]i and myosin light chain phosphorylation increased in response to oxytocin and angiotensin II. These findings indicate that a number of uterotonic agents effect an increase in [Ca2+]i, which in turn causes phosphorylation of myosin light chain. Furthermore, the concentration of Ca2+ in the cytoplasm is a primary determinant for myosin light chain phosphorylation in human myometrial smooth muscle cells.

Intracellular angiotensin II activates rat myometrium

“…5). A similar mechanism has been demonstrated in renal proximal tubule cells (12, 23, 32, 44, 49) and is consistent with the accepted contractile effect of angiotensin II on the myometrium, which involves AT 1 receptor activation and elevation of [Ca 2ϩ ] i (23,28,32).…”

Mobilization of calcium by the brief application of oxytocin and prostaglandin E2 in single cultured human myometrial cells

“…This high concentration was used in order to obtain a maximal cellular response. (Mackenzie et al 1990), in contrast to their action in other cell types (Davis et al 1987;Mene et al 1987;Yokohama et al 1988 (Fig. 3 A).…”

“…It is believed that contraction is preceded by an increase in intracellular calcium concentration ([Ca21]1) (Carsten & Miller, 1987). Calcium associates with calmodulin to form a calcium-calmodulin complex thereby activating myosin light chain kinase which phosphorylates myosin (Janis, Barany, Barany & Sarmiento, 1981;Mackenzie, Word, Casey & Stull, 1990). Interaction of the phosphorylated myosin light chains with actin causes muscle contraction (Pato & Adelstein, 1980;Haeberle, Hathaway & DePaoli-Roach, 1985).…”

The effects of inhibiting myosin light chain kinase on contraction and calcium signalling in human and rat myometrium

“…The main force-activating pathway is taken to be Ca 2+ -calmodulin activation of myosin light chain kinase (MLCK) and phosphorylation of myosin light chains [28]. An increase in phosphorylated myosin with contraction has been shown to occur in the human myometrium [12]. Recently, however, it has been become clear that agonists can modify this process [8].…”