Insulin induces cation fluxes and increases intracellular calcium in the HTC rat hepatoma cell line

BACKGROUND/AIMS: Rat hepatoma HTC cells were used to study conductive pathw ays implicated in insulin induced cation and calcium influx into liver cell s. METHODS: Membrane potentials and currents were measured by whole cell parch clamp. Cytosolic calcium was measured using FURA-2 fluorescence. RESULTS: Insulin induced a gradual and reversible depolarization of 5.7+/-0 .8 mV. Insulin-induced currents showed a linear slope conductance of 663 pS and a reversal potential of -17.9 mV. Ion substitution experiments showed that these currents were composed mainly of a nonselective cation component . In FURA 2 experiments, insulin caused a slow monophasic rise in HTC cell calcium, which depended on the presence of extracellular calcium. Insulin a lso induced significant increases of 1.58- and 1.54-fold in basal calcium i nflux when studied by external calcium withdrawal and readmission, or by th e manganese quench method, respectively. Using the latter approach, we foun d that 100 mu M gadolinium and 10 mu M SKF96365 blocked the rise of the bas al manganese quench race induced by insulin whereas 100 mu M verapamil was without effect. CONCLUSIONS: Insulin induces inward cation currents that depolarize HTC cel l membrane potentials and participate in increased calcium influx.