[Effect of increased mechanical loading on the relation between the contraction of isolated cardiac muscle and the concentration of Ca++ in the perfusate]. / Vliianie povyshennoi mekhanicheskoi nagruzki na zavisimost' sokrashcheniia izolirovannoi serdechnoi myshtsy ot kontsentratsii Ca++ v perfuzate.

The distension of isolated papillary muscles working isotonically or a transition to isometric working entailed an increased sensitivity of the contractile velocity to changes in perfusate Ca++ concentration. After sudden fall in Ca++ concentration, a more rapid decline of the contractile velocity in isometric mode was observed as compared to isotonic mode of working. The similar difference was found in experiments on isolated guinea pig heart working in isovolumic or auxotonic modes, though the rate of Ca++ loss by the heart was the same. The results suggest that an increased mechanical load may diminish the ability of myocardial cells to compensate for the changes in external Ca++.