Subcellular Ca2+ transport le different areas of dog heart

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Abstract
Ca transport and ATPase activities were determined in the heavy microsomal and mitochondrial fractions isolated from the left and right atria and ventricles of dogs. Ultrastructural distribution of these organelles in different areas of the myocardium was examined. Ca binding, uptake and Ca ATPase activities of the atrial microsomes were lower than those of the ventricles. Mitochondrial Ca binding and uptake activities in the right atrium were higher than those in other areas. The mitochondrial total ATPase activities in the atria were higher than those in the ventricles. Mitochondrial and microsomal yields from ventricles were significantly higher. Size and number of mitochondria in the ventricles were greater but no striking difference in the distribution of sarcoplasmic reticulum was apparent in different areas of the heart. Poorly developed Ca transport functions in the atrial microsomes may be one factor responsible for the generation of lower contractile force in this tissue in comparison with the ventricle.

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