Insulin induces cation fluxes and increases intracellular calcium in the HTC rat hepatoma cell line.
OBJECTIVE
Rat hepatoma HTC cells were used to study conductive pathways implicated in insulin-induced cation and calcium influx into liver cells.


METHODS
Membrane potentials and currents were measured by whole-cell patch 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 also induced significant increases of 1.58- and 1.54-fold in basal calcium influx when studied by external calcium withdrawal and readmission, or by the manganese quench method, respectively. Using the latter approach, we found that 100 microM gadolinium and 10 microM SKF96365 blocked the rise of the basal manganese quench rate induced by insulin whereas 100 microM verapamil was without effect.


CONCLUSIONS
Insulin induces inward cation currents that depolarize HTC cell membrane potentials and participate in increased calcium influx.
Mathé
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Groupe de Recherche en Transport Membranaire et Département de pharmacologie, Université de Montréal, Montréal, Québec, Canada.
Vallerand
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D
Haddad
P S
PS
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000502:physiology*; D008099:Liver / Q000166:cytology*; D008114:Liver Neoplasms, Experimental / Q000503:physiopathology*; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D051381:Rats; D014407:Tumor Cells, Cultured
D002412:Cations; D007328:Insulin; D002118:Calcium