Effects of ouabain on tissue calcium and calcium exchange in pacemaker of turtle heart

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Abstract
The effects of ouabain in positive inotropic (10–7 m) and toxic (10–6 m) concentrations on the tissue calcium content and exchange in the sinus venosus or pacemaker, atrium, and ventricle of the spontaneously beating, in situ, perfused turtle heart were compared. Tissue calcium was measured with a flame photometer, and calcium exchange was determined by the use of Ca45. Solutions were prepared in a cold-blooded animal Ringer's solution. Heart rate remained constant during perfusion with 10–7 m ouabain, but the 10–6 m concentration produced varying arrhythmias. The toxic concentration produced an increase in tissue calcium in all chambers. 10–7 m Ouabain produced an increased calcium exchange in all chambers and a drop in tissue calcium in the pacemaker. The calcium content of the atrium and ventricle remained unchanged at this concentration. The decrease in pacemaker calcium is interpreted as a release of calcium by ouabain allowing the calcium to pass down a concentration gradient into the medium.

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