EFFECT OF METABOLIC INHIBITION ON INTRACELLULAR CA2(-CHAIN AND FORCE IN RAT SMOOTH-MUSCLE(), PHOSPHORYLATION OF MYOSIN REGULATORY LIGHT)

1. The effect of the inhibition of oxidative phosphorylation on intrac ellular calcium concentration ([Ca2+](i)), phosphorylation of the 20 k Da regulatory light chain of myosin (MLC(20)) and contractility was in vestigated in isolated longitudinal smooth muscle from rat uteri. 2. C yanide (2 mM) application to normally polarized preparations resulted in an elevation of basal [Ca2+](i) but an inhibition of [Ca2+](i) tran sients and the accompanying contractions. 3. Depolarization with high- K+ solution (40 mM KCl) resulted in elevation of [Ca2+](i) and maintai ned force production. Phosphorylation of MLC(20) was transiently incre ased followed by a Steady-state augmentation above resting levels.4. C arbachol (100 mu M) produced a transient elevation of [Ca2+](i) and fo rce of depolarized tissues followed by a steady-state augmentation of both parameters. PGF(2 alpha) (1 mu M) did not significantly potentiat e [Ca2+](i) or force in depolarized preparations. Both carbachol and P GF(2 alpha) potentiated phosphorylation of MLC(20) in depolarized tiss ues. 5. Addition of cyanide to depolarized preparations, in the presen ce or absence of carbachol or PGP(2 alpha) resulted in significant att enuation of force under each condition. The magnitude and normalized r ates of force inhibition by cyanide were not significantly different f or each stimulus condition. MLC(20) phosphorylation levels were unalte red by cyanide treatment. However, cyanide increased the maintained le vel of [Ca2+](i) under each experimental protocol. 6. It is concluded that the inhibition of oxidative phosphorylation with cyanide results in dissociation of both the [Ca2+](i)-force and MLC(20) phosphorylatio n-force relationships in rat uterine smooth muscle.