Insulin increases the density of potassium channels in white adipocytes: possible role in adipogenesis.
We studied the potassium currents in white adipocytes obtained by culturing preadipocytes from rat epididymal tissue, both with insulin (WA(i)) and without insulin (WA(o)), in order to test the role of insulin in the development of voltage-gated potassium channels (K(v)) during adipogenesis. Occasionally, very small potassium currents (I(K,V)) were present in preadipocytes; however these currents were measured in all differentiated cells (adipocytes). WA(i) exhibited greater macroscopic potassium currents than WA(o) with no apparent differences in kinetics or voltage dependence. The current density (pA/ micro m(2)) calculated in WA(i) was higher than in WA(o). Currents were blocked by millimolar concentrations of tetrethylamonium (TEA). The effect of insulin on adipogenesis, both with and without TEA, was analysed. Four days without insulin and three days with insulin were necessary to increase the total number of cells in culture by 2.5-fold. Insulin increased the number of differentiated cells by 73.5%. Cell proliferation and differentiation were inhibited by TEA. Proliferation was affected only by high concentration of TEA. Inhibition of differentiation was dose dependent, with the concentration necessary for half-block similar to the IC(50) values to block potassium channels. These results suggest that insulin increases the density of K(v) and that these channels may be necessary for the normal growth of white adipocytes in culture.