Calcium movements during potassium contracture in isolated rabbit aortic strips

Abstract

Ca movements and tissue Ca concentrations were determined during K₂SO₄-induced contractures in isolated rabbit aortic strips. The initiation and maintenance of the contractures were both dependent on the presence of Ca and associated with an increase Ca influx. There was a 2.8-fold increase in Ca influx in the initial period and a 1.9-fold increase during the sustained phase of the contracture as compared to controls in Ringer's solution. Furthermore, Ca influx during K₂SO₄ contracture was dependent on the extracellular Ca concentration up to approximately 0.3 mm and there was a linear relationship between the tension developed and the rate of entry of Ca. There was no significant difference in the tissue Ca concentration after K₂SO₄ contractures as compared to controls in Ringer's solution. The data were interpreted to suggest that contracture was initiated by an influx or release of Ca into the vicinity of the contractile elements of the aorta and that the maintenance of the contracture was dependent on a sustained level of ionized Ca in this region.