Tension-Ca2+ concentration relationship in chemically skinned vascular smooth muscle of the frog.

Vascular smooth muscle of the frog was skinned by 0.2 mg/ml saponin for 20 mm. The skinned preparations activated by Ca2+, at 2 mmol/l Mg2+ and MgATP2-, gave half maximal force at Ca2+ = (1.32 +/- 0.07) x 10(-6) mol/l and maximal force at Ca2+ = 3.16 x 10(-5) mol/l (35 +/- 4% of the maximal contraction induced by KCl in living smooth muscles). The Hill coefficient was 1.51 +/- 0.11. Thus, the skinned vascular smooth muscle of the frog has Ca2+ sensitivity similar to that of various preparations from a variety of muscle types; the slope of the tension-pCa curve obtained was similar to that typical of mammalian smooth muscles.