title: Effects of divalent and trivalent cations on Na+-Ca2+ exchange in cardiac sarcolemmal vesicles.
abstract: Inhibition of Na+-Ca2+ exchange processes in canine cardiac sarcolemmal vesicles by several divalent and trivalent cations has been investigated. The order of cation effectiveness in inhibiting initial rates of Nai+-induced Ca2+ uptake in the presence of 140 mM Nai+ and 20 microM Cao2+ is La3+ greater than Nd3+ greater than Tm3+ approximately Y3+ greater than Cd2+ much greater than Sr2+ greater than Ba2+ approximately Mn2+ much greater than Mg2+. The effectiveness of the divalent ions is related to their ionic crystal radius as compared with that of Ca2+. No such relationship was observed for the trivalent ions, which appeared instead to be more effective the larger their radius. Very low concentrations of trivalent ions ((1-6).10(-7)M) caused slight stimulation of Ca2+-exchange uptake. The trivalent ions also inhibited passive and Nao+-induced Ca2+ efflux from sarcolemmal vesicles, in the same concentration range as that for inhibiting uptake. The divalent ions, however, stimulated Ca2+ efflux, possibly via divalent cation-Ca2+ exchange. These various results suggest that the divalent and trivalent cations interact differently with the exchange apparatus in the sarcolemma.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002412:Cations / Q000494:pharmacology*; D004285:Dogs; D006321:Heart / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D012508:Sarcolemma / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
chemical_list: D002412:Cations; D012964:Sodium; D002118:Calcium