Sodium-dependent uptake of orthophosphate (Pi) into skeletal muscle plasma membrane vesicles.

Despite the central bioenergetic importance of inorganic phosphate (Pi), little is known about the control of Pi metabolism in skeletal muscle, where resting [Pi] is maintained at 2-4 mM despite a highly unfavourable electrochemical gradient, and is partially regulated against changes in extracellular [Pi] [ I ,2]. We have discussed elsewhere how cellular [Pi] can be controlled by active transmembrane Pi transport [3] and have previously described a Na-dependent Pi uptake in cultured L6 myoblasts [ l ] . We now report a characterisation of Pi uptake in sarcolemmal and t-tubule vesicles derived from leg muscle of young (<lkg) female New Zealand White rabbits.