Evidence for a sodium-dependent calcium influx in isolated rat hepatocytes undergoing ATP depletion

ATP depletion caused by menadione and triethyllead in isolated hepatocytes is associated with intracellular acidosis and a sustained increase in intracellular Na⁺ and Ca²⁺ concentrations. Removal of Na⁺ from the incubation medium as well as the inclusion of EGTA largely prevented the increase in cytosolic Ca²⁺, thus indicating that Ca²⁺ was mobilized from the extracellular medium in response to Na⁺ load. To further validate these findings, hepatocytes were incubated with a combination of sodium propionate and ouabain in order to induce intracellular acidosis and inhibit Na⁺ extrusion. This treatment promoted a marked increase in intracellular Na⁺ and Ca²⁺ concentrations that was prevented by omission of Na⁺ from the incubation medium as well as by agents that inhibited cellular Na⁺ influx. These data indicate that following Na⁺ load, Ca²⁺ can be accumulated in hepatocytes via a Na⁺/Ca²⁺ antiporter operating on a reverse mode.