[The effect of alpha 1-stimulation and lithium on the calcium sensitivity of hyperpermeable myocardial fibers in the rat].

Effects of alpha 1-adrenoagonist phenylephrine (PhE) and lithium, an inhibitor of inositolmonophosphatase, on calcium sensitivity of hyperpermeable rat myocardial fibers were studied. In the presence of propranolol, PhE reduced calcium sensitivity, and this effect was enhanced as calcium concentration was being increased during stimulation with PhE. This appears to relate to an activation of protein kinase C by calcium. LiCl also decreased calcium sensitivity of fibers. This result partially can be explained by a direct effect of Li+ on myofibrils. A combination of PhE and LiCl decreased calcium sensitivity even more, but the effect of PhE in this case was less expressed than in the absence of LiCl. Prasozin, an alpha 1-adrenoblocker, prevented from the effect of PhE both in the presence and in the absence of lithium, thus indicating that stimulation of alpha 1-adrenoceptors was involved in the effects of PhE and lithium observed in this study.