Effect of the kinase inhibitor, H-7, on stress, crossbridge phosphorylation, muscle shortening and inositol phosphate production in rabbit arteries.

Smooth muscle contractile agents cause large increases in crossbridge phosphorylation (Mp) and cycling rates resulting in the rapid development of stress (force/muscle cross-sectional area). Despite temporal declines in Mp and cycling during continued activation, stress is maintained at high levels. This observation led to several different hypotheses describing the regulation of steady-state stress. One proposal is that protein kinase C regulates stress maintenance, whereas another invokes a steady-state dependence on Ca+(+)-calmodulin-dependent myosin light chain kinase. The aim of this study was to investigate the mechanism of stress-maintenance by analyzing the inhibitory efficacy of a protein kinase C inhibitor, H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperizine], on steady-state values of stress, Mp and crossbridge cycling in rabbit renal and femoral arteries. H-7 effectively inhibited steady-state stress produced by KCl (IC50 = 3.7-4.4 microM) and phenylephrine (PhE) (IC50 = 10.6-15.2 microM). Likewise, increases in the level of Mp and the rate of crossbridge cycling induced by both KCl and PhE were significantly reduced by 10 microM H-7. H-7 did not reduce inositol phosphate production stimulated by PhE, but did reduce early stress development thought to be mediated by inositol phosphate-induced mobilization of intracellular calcium. Calcium-induced increases in stress and Mp produced in saponin-skinned artery strips were reduced by less than 50% by 320 microM H-7.(ABSTRACT TRUNCATED AT 250 WORDS)