Contractile properties of skinned preparations from ischaemic canine myocardium and coronary arteries.

The influence of prolonged ischaemia on the regulation of contraction in the myocardium and in the smooth muscle of coronary arteries was investigated. Chemically skinned preparations were used which enabled the contraction to be studied with the environment of the contractile filaments controlled. Myocardial ischaemia was produced in anesthetized adult beagle dogs by occlusion of the left anterior descending artery for 3 h and followed by 30 min reperfusion. Myocardial tissue and segments from coronary arteries were obtained from the ischaemic infarcted wall region ("in vivo ischaemic") and compared with control preparations from perfused coronary arteries and from the free wall of the left ventricle. Coronary and myocardial preparations were also obtained from the heart after a 3 h period in vitro under anoxic conditions at 37 degrees C ("in vitro ischaemic") simulating a state of extreme ischaemia. Control myocardial fibres were fully relaxed at pCa (-log-[Ca2+]) 9 and developed 24 +/- 5% (n = 7) of maximum force at intermediate calcium concentration (pCa 5.5). In contrast, the in vivo and in vitro ischaemic preparations produced force at pCa 9 (28 +/- 13 and 39 +/- 8%, respectively, n = 5 and 7) and showed an increased force development at pCa 5.5 (53 +/- 11 and 75 +/- 5%). The in vivo and in vitro ischaemic coronary arteries relaxed more slowly following calcium removal than control vessels. The in vitro ischaemic vascular preparations developed active force at pCa 9 and showed increased levels of myosin light chain phosphorylation and reduced phosphatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)