PROTEIN-KINASE-C ISOFORMS IN IRIS SPHINCTER SMOOTH-MUSCLE - DIFFERENTIAL-EFFECTS OF PHORBOL ESTER ON CONTRACTION AND CAMP ACCUMULATION ARE SPECIES-SPECIFIC

Objectives were to identify PKC isoforms in iris sphincter isolated fr om rabbit, cat, dog and bovine irides, to determine their subcellular distribution, and to investigate the effects of the phorbol ester, PDB u, on contraction and cAMP accumulation in this tissue. Using six isof orm (alpha, beta, gamma, epsilon, delta, zeta)-specific polyclonal ant ibodies, PKC alpha, beta, epsilon, delta, and zeta were detected in th e four species, whereas PKC gamma was detected only in dog and bovine. PKC alpha and epsilon are the most abundant isoforms in this tissue. PKC alpha is mainly cytosolic in rabbit and bovine and membrane associ ated in cat and dog. PKC gamma is equally distributed in cytosol and m embrane fractions of bovine, but mostly cytosolic in dog. PKC beta, de lta and epsilon are mainly membraneous and PKC gamma is mainly cytosol ic in all species. PDBu (100 nM) induced a contractile response in rab bit- and cat-, but not in dog and bovine, sphincters, and increased cA MP accumulation in rabbit, cat, dog and bovine by 111, 130, 458 and 29 4%, respectively. Therefore, the lack of effect of PDBu on contraction in dog and bovine, as compared to rabbit and cat, may be due: (a) to the presence of PKC gamma isoform, and (b) to the stronger stimulatory effects of the phorbol ester on cAMP production in the non-contractin g species. In addition to demonstrating the presence of various PKC is oforms in the iris sphincter and the activation of adenylyl cyclase by this protein kinase, we have shown that the distribution of the PKC i soforms in this tissue is species specific. Furthermore, our data sugg est that there may be specific physiological functions associated with each of the PKC isoforms and that PKC is involved in the contractile response of some but not all smooth muscles.