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Abstract
The structure and function of the sarcolemma's superficial layers and the sarcolemma's dependence upon [Ca] 0 was studied in the isolated arterially perfused rabbit interventricular septum. Perfusion of tissue for 20 min with 0 Ca (< 5 μ m) solution produced a distinctive separation of membrane superficial laminae. These separations were found to be irreversible and associated with an increased cellular 45Ca content and irreversible contracture when normal [Ca] 0 was reperfused. Perfusion with 50 μ m Ca produced no alteration of membrane structure, contractile function or 45Ca uptake. 0 Ca perfusion resulted in a 14% mean cellular 42K loss and this appeared to be independent of superficial membrane separations. Mg supplements in 0 Ca perfusate resulted in membrane separations and contracture intermediate to those of 0 Ca without supplements and 50 μ m Ca; Mg supplements completely protected against cellular K loss. Zero [Ca]-induced separation of superficial laminae correlates with increased Ca permeability and suggests that this membrane region is involved in the control of contractile Ca. Ca ion is also essential for control of K permeability, probably in the lipid bilayer. The importance of the presence of [Ca] 0 to the normal structure and function of these membrane sites is emphasized.
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