ROLE OF PROTEIN-KINASE-C IN RELATIONSHIP BETWEEN CA2-TOXIN-PERMEABILIZED MESENTERIC-ARTERY( AND CONTRACTILE ELEMENTS IN RAT ALPHA)

Phorbol ester, which activates protein kinase C (PKC), modulates vasoc onstrictor-induced tension in vascular smooth muscle. Recently, Staphy lococcal aureus alpha-toxin, which produces too small pores in the pla sma membrane to allow passage of proteins, such as PKC, is used to inv estigate the signal transduction system in vascular smooth muscle cell s. In order to elucidate the role of PKC on vascular smooth muscle con traction, we examined whether PKC activation influences the relationsh ip between intracellular Ca2+ ([Ca2+](i)) and tension in Wistar rat su perior mesenteric artery (SMA) using vascular smooth muscle permeabili zed with Staphylococcal alpha-toxin. [Ca2+](i) was clamped at specifie d values (10(-8.5)-10(-4) mol/L) using EGTA-Ca2+ buffer. In alpha-toxi n non-treated rings of SMA, isometric tension was evoked by 10 mmol/L caffeine and 10-30 mmol/L external potassium (high K+) in the absence or presence of phorbol 12, 13-dibutyrate (PDBu), a PKC activator, 1-(5 -isoquinolinesulfonyl)-2-methylpiperazine (H-7), and staurosporine (PK C inhibitors). PDBu significantly augmented caffeine- and high K+-evok ed contractions. H-7 and staurosporine significantly attenuated caffei ne- and high K+-evoked contractions augmented by PDBu. Moreover, H-7 s ignificantly suppressed high K+-induced contraction in the absence of PDBu. In alpha-toxin permeabilized artery, PDBu shifted the [Ca2+](i)- force relationship curve to the left. These results suggest that PKC a ctivates vascular smooth muscle contraction by increasing the sensitiv ity of the contractile apparatus to Ca2+.