Abstract
In this work, we compared the effect of K + on vesicles derived from the longitudinal (LSR) and terminal cisternae (HSR) of rabbit white muscle. In HSR, K + was found to inhibit both the Ca 2+ accumulation and the heat released during ATP hydrolysis by the Ca 2+-ATPase (SERCA1). This was not observed in LSR. Valinomycin abolished the HSR Ca 2+-uptake inhibition promoted by physiological K + concentrations, but it did not modify the thermogenic activity of the Ca 2+ pump. The results with HSR are difficult to interpret, assuming that a single K + is binding to either the ryanodine channel or to the Ca 2+-ATPase. It is suggested that an increase of K + in the assay medium alters the interactions among the various proteins found in HSR, thus modifying the properties of both the ryanodine channel and SERCA1.
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