[Role of calcium on the contraction induced by potassium and norepinephrine in the sheep rumen].

The effect of calcium on the contractile responses induced by high K+ solutions and noradrenaline has been investigated Ca2+-free-solutions and two selective antagonists of calcium channels (verapamil and sodium nitroprusside) have been used. Both types of responses were inhibited by Ca2+-free-solutions. Contractions induced by high K+ solutions were inhibited by verapamil, but not by sodium nitroprusside. However, the responses to noradrenaline were specifically inhibited by sodium nitroprusside. These results suggest that in rumen circular smooth muscle of the sheep there are two types of calcium channels, a voltage-dependent Ca2+ channel and receptor-linked Ca2+ channel.