Membrane Ca2+ fluxes in rat hepatoma cells exposed to a supraphysiological concentration of asparagine.

It has been shown that supraphysiological concentrations of asparagine and hypoosmotic shock stimulate ornithine decarboxylase activity in cultured cancer cells by increasing the synthesis and the half-life of the enzyme protein. Since extracellular Ca2+ is essential for the action of asparagine and is also important for cell volume regulation in certain cell types, aspects of Ca2+ physiology in asparagine-treated H-35 rat hepatoma cells were investigated. The initial rate of influx of 45Ca increased from 0.25 to 1.04 nmol/min/mg protein immediately after exposure to 10 mM asparagine. With a one-minute lag the efflux rate also increased 2.2-fold over a five minute period. Asparagine did not cause a net-gain in cellular Ca2+ as measured by 45Ca equilibration, nor did it have any effect on the cytosolic free Ca2+ as measured by Fura-2 fluorescence spectroscopy and Fluo-3 fluorescence confocal microscopy.