epsilon-Isoenzyme of protein kinase C induces a Ca2+-independent contraction in vascular smooth muscle

We provide here the first direct evidence for in situ functional specificity of protein kinase C (PKC)-epsilon as a regulator of smooth muscle contractility. PKC is known to cause a Ca2+-independent contraction of ferret aortic smooth muscle, and the expression of two Ca2+-independent PKC isoenzymes, epsilon and zeta, has been demonstrated in this tissue. To test directly the hypothesis that one of these isoenzymes regulates contractility, constitutively active forms of PKC-epsilon and PKC-I were applied to saponin-permeabilized single ferret aortic smooth muscle cells. PKC-I caused no significant force response, but PKC-epsilon induced contraction of a magnitude (105 +/- 8 mu g) similar to that produced by phenylephrine (110 +/- 10 mu g), a relatively selective alpha(1)-adrenergic agonist that triggers a PKC-dependent contraction. The PKC-epsilon-induced contraction was reversed by the PKC pseudosubstrate inhibitory peptide, PKC19-31. The myosin light chain kinase inhibitor 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine (ML-9) did not affect the force response of PKC-epsilon-activated cells, suggesting that PKC-E may induce this contraction solely via thin filament disinhibition. In support of this conclusion, calponin and caldesmon were shown to be good in vitro substrates of PKC-epsilon but not of PKC-zeta.