Isozyme-specific inhibitors of protein kinase C translocation: Effects on contractility of single permeabilized vascular muscle cells of the ferret

1. The effects on contractility of three peptides reported to inhibit protein kinase C (PKC) translocation in an isozyme-specific manner were studied: a peptide from the C2 domain of conventional PKCs (C2-2), a peptide from the N-terminal variable domain of εPKC (εV1-2) and a peptide (ABP) from the actin-binding domain of εPKC (ε(223-228)). 2. Isometric force was directly recorded from individual hyperpermeable ferret portal vein or aortic smooth muscle cells. 3. Phenylephrine contracted permeabilized portal vein cells at pCa 6.7 but not at pCa 7.0. However, phenylephrine did contract aortic cells at pCa 7.0. 4. C2-2 inhibited phenylephrine-induced contraction, but did not affect resting tension: in portal rein cells at pCa 6.7. In aortic cells at either pCa 6.7 or 7.0, C2-2 had no effect on either basal tension or phenylephrine-induced contraction, 5. ABP did not evoke any changes in phenylephrine-induced contraction or baseline tension in either portal vein or aortic cells. 6. εV1-2 inhibited phenylephrine-induced contraction and decreased resting tension in aortic cells at pCa 7.0, but not in portal vein cells at pCa 6.7. 7. Western blot indicated that, portal vein cells contained substantially more αPKC than aortic cells. Portal vein cells also contained small amounts of βPKC, which was undetectable in aortic cells. In contrast, aortic cells contained more εPKC than portal vein cells. Even though εPKC was expressed in portal vein and αPKC in aorta, imaging studies indicated that they were not translocated in these cell types. 8. These results suggest that the Ca²⁺-dependent isozymes of PKC (α and/or β) play a major role in contraction of the portal vein but not of the aorta. In contrast, the results are consistent with εPKC, but not Ca²⁺-dependent PKC isozymes, regulating contractility of the aorta.