Prokopczuk A. and Pytkowski В.: Effect of inhibitors of slow calcium current on resting calcium efflux from cat papillary muscles. Acta physiol, pol., 1989, 40 (5-6): 564-568. Examination of influence of divalent cations (Co²⁺, Ni ²⁺, Mn²⁺ and organic blockers (verapamil and D600) on calcium efflux from resting mammalian myocardium shows that they either inhibit or increase transiently 45Ca²⁺ efflux, depending on the site of action. It seems that those agents whose sites of action are limited to the sarcolemma inhibit Ca²⁺ efflux. Co²⁺, Ni²⁺, verapamil and D600 belong to this group. Mn²⁺ ions which act also apparently on intracellular structures increase transiently Ca²⁺ efflux. Such a finding illustrates a diversity in mechanisms of action in a group of agents generally classified as calcium channel blockers.
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We investigated in the single myocytes of rat heart the effect of blocking of ATP-ase of sarcoplasmic reticulum (SR) on mitochondrial Ca2+ uptake and release. Mitochondrial Ca2+ content was investigated as Mn2+ - resistant fluorescence of Indo 1 - AM loaded into cells. SR ATP-ase was blocked with 10-6 M thapsigargin (Tg). Tg blocked almost completely stimulation Œdependent mitochondrial Ca2+ uptake and slowed down its release despite that the maximal cytosolic Ca2+ concentration was not decreased. We propose that mitochondrial stimulation -dependent Ca2+ uptake is greatly enhanced by [Ca2+ ] built by SR in microdomains adjacent to these organelle.