Cytosolic Ca2+ and protein kinase C (PKC) may regulate the myogenic contraction of arterial myocytes. The role of these second messengers is examined in skeletal muscle small arteries, which have strong myogenic activity, and mesenteric small arteries, which have weak myogenic activity. The vessels were isolated and cannulated. The inner diameter was measured with a video-digitizing system. Cytosolic Ca2+ concentration was assessed by fura 2. Skeletal muscle small arteries dilated from 122 +/- 6 to 153 +/- 6 microm immediately after the transmural pressure change from 40 to 100 mmHg and constricted to 121 +/- 5 microm (myogenic contraction) with an increase in the 340/380 fluorescence ratio (by approximately 33%) in control vessels. Nifedipine abolished myogenic contraction and the increase in the fluorescence ratio. PKC inhibitors (H7 and staurosporine) abolished myogenic contraction but did not depress the increase in the fluorescence ratio. In mesenteric small arteries, myogenic contraction was insignificant in control vessels. A relatively low dose of PKC activator (4.4 +/- 1.4 nmol/l) elicited myogenic contraction, but a higher dose (21 +/- 6 nmol/l) depressed it. Thus the cytosolic Ca2+ increase and PKC activity may cooperatively act on the myogenic contraction of skeletal muscle small arteries. The activity of PKC should play an important role in myogenic contraction of rat small arteries.