ANGIOTENSIN-II AND CONTRACTION OF ISOLATED MYOCYTES FROM HUMAN, GUINEA-PIG, AND INFARCTED RAT HEARTS

The effects of angiotensin II on myocardial contractility were assesse d in isolated cardiac myocyte preparations, using video microscopy wit h a computerized edge-detection system, Angiotensin II (1 nM-10 mu M) did not-affect the contraction of rat (n = 10), guinea pig (n = 11), o r human ventricular myocytes (n = 8) or of human atrial myocytes (n = 12). Isoproterenol or raised extracellular calcium increased the contr action amplitude of the cardiac myocytes to a maximum of between 150 a nd 560% above basal, and there were corresponding increases in the vel ocities of contraction and relaxation. In rat and guinea pig ventricul ar myocytes 1 mu M angiotensin II did not-affect the inotropic respons e to isoproterenol. Seven days after left coronary artery ligation in seven rats, the basal contraction amplitude was reduced in myocytes fr om the infarcted region (4.0 +/- 1.98) compared with the noninfarcted region (5.0 +/- 2.8%, P = 0.03) and with myocytes from six sham-operat ed hearts (5.0 +/- 2.8%, P = 0.03). There was a switch in myosin isofo rm expression from the V-1 to the V-3 isoform in myocytes from both th e infarcted and noninfarcted regions. Angiotensin II (1 nM-10 mu M) ha d no significant effect on the contraction characteristics of myocytes from the infarcted rat hearts. In conclusion, angiotensin II had no s ignificant inotropic effect on isolated cardiac myocyte preparations f rom guinea pig ventricle, normal and infarcted rat ventricle, human ve ntricle, and human atrium.