Calcium distribution and transport in myelinated nerve
The effects of metabolic inhibitors on ATP levels and on 45Ca fluxes were studied in desheathed tibial nerves of Rana pipiens. ATP levels were significantly reduced and Ca influx and efflux increased following exposure to cyanide, mersalyl, azide, dinitrophenol, iodoacetate or ethacrynic acid. The efflux changes were relatively small compared to squid axons but are not attributable to depolarization of the cell or to changes in the transmembrane Na gradient. The magnitude of the effluxes are consistent with ideas about the amount of labile Ca sequestered in energy-dependent Ca pools. The efflux stimulated by metabolic inhibitors is reduced by removing extracellular Na or Ca, indicating that a large portion of Ca efflux in the poisoned state is mediated by Na-Ca countertransport. In the nominal absence of both these cations Ca efflux can be stimulated by metabolic inhibitors, suggesting that mechanisms in addition to countertransport participate in Ca efflux.