Influence of extracellular calcium and calcium antagonists on contractions induced by potassium and prostaglandin F2α in isolated cerebral and mesenteric arteries of the cat

Abstract

1 The effects of a number of calcium antagonists (diltiazem, nifedipine, nimodipine and verapamil) have been studied on feline isolated pial arteries contracted by potassium (127 mM) or prostaglandin F_2α (PGF_2α, 2.5 μM) and mesenteric arteries contracted by potassium (127 mM). 2 Withdrawal of Ca²⁺ from the extracellular medium for 30 min reduced the contractile response to potassium in cerebral vessels by 92% and in mesenteric vessels by 96%. Subsequent addition of Ca²⁺ caused reproducible contractions which were inhibited by both nifedipine and nimodipine. 3 The four calcium antagonists relaxed the isolated middle cerebral artery contracted either by potassium or PGF_2α, and mesenteric arteries contracted by potassium, in the following order of potency: nimodipine > nifedipine > verapamil > diltiazem. 4 Nimodipine was more potent than nifedipine in cerebral arteries, and more potent in cerebral than in mesenteric arteries. Otherwise, the potassium-contracted cerebral and mesenteric vessels showed no major differences in sensitivity to calcium antagonists.