Change of Ca2+ requirement for myosin phosphorylation by prostaglandin F2 alpha

• Published in: The American journal of physiology Vol. 261; no. 2 Pt 1; p. C253
• Main Authors: Suematsu, E, Resnick, M, Morgan, K G
• Format: Journal Article
• Language: English
• Published: United States 01.08.1991
• Subjects: Animals; Aorta - metabolism; Calcium - physiology; Dinoprost - metabolism; Ferrets; Male; Muscle Contraction - physiology; Myosins - metabolism; Osmolar Concentration; Phosphorylation; Potassium - pharmacology; Regression Analysis
• ISSN: 0002-9513; 2163-5773
• DOI: 10.1152/ajpcell.1991.261.2.c253

The mechanism of contraction of vascular smooth muscle by prostaglandin F2 alpha (PGF2 alpha) was examined by simultaneous measurement of the intracellular Ca2+ concentration [( Ca2+]i), force, and myosin light-chain (MLC) phosphorylation in ferret aorta. In the presence of 2.5 mM extracellular Ca2+, PGF2 alpha (10(-5)M) produced a tonic contraction with a transient spike in [Ca2+]i, followed by a relatively small sustained increase in [Ca2+]i (from a basal level of 2.32 +/- 0.07 x 10(-7) to 2.72 +/- 0.05 x 10(-7) M). In Ca(2+)-free bathing media, PGF2 alpha also produced a tonic contraction with a small spike in [Ca2+]i, indicating a release of Ca2+ from intracellular store sites, followed by no significant increase in [Ca2+]i. Ca(2+)-force curves were constructed by plotting the calibrated steady-state aequorin light signal against the resulting steady-state force. The curve was significantly shifted to the left by PGF2 alpha. PGF2 alpha also shifted the Ca(2+)-phosphorylation curve to the left. These results suggest that PGF2 alpha causes contraction by both elevating [Ca2+]i and decreasing the Ca2+ requirement for MLC phosphorylation. The data are consistent with a mechanism where there is either an increase in activity of MLC kinase or a decrease in phosphatase activity. Additionally, there was a smaller, but statistically significant, effect to increase force at any one phosphorylation level, pointing to the possibility of regulation of contractile force separate from MLC phosphorylation.