Recently, there has been a dramatic increase in the incidence of obesity resulting from an excess of white adipose tissue. This obesity may occur as a result of the enlargement of existing adipocytes and/or as a consequence of an increase in new fat cells. Although multiple factors modulate proliferation and differentiation of adipocytes, it is known that some hormones and growth factors act via specific receptors to transduce external growth and differentiation signals through a cascade of intracellular events. Insulin is able to stimulate cell proliferation in white adipose tissue and increases the number of differentiated cells for most primary preadipocytes. Experiments with other cell types have implicated potassium channels as being essential for their proliferation and differentiation. It has been demonstrated that functional voltage-gated potassium channels may be necessary for the normal proliferation and differentiation of brown fat cells in culture and that the purinergic modulations of these potassium currents may be important for altering adipocyte growth and development.

In white adipocytes, obtained by culturing preadypocytes from epididymal tissue of rats that had been humanely killed, we demonstrated the existence of voltage-dependent K⁺ channels (Kv) using the whole-cell variant of the patch-clamp technique (Ramírez-Ponce et al. 1996). In a previous study carried out by means of intracellular recording, we showed that insulin modulates K⁺ conductances in white adipocytes (Ramírez-Ponce et al. 1991).

In this work we studied the potassium currents in white adipocytes obtained by culturing preadipocytes from rat epididymal tissue, both with insulin (WAi) and without insulin (WAo), in order to test the role of insulin in the development of voltage-gated potassium channels (Kv) during the adipogenesis. Occasionally, very small potassium currents (I_KV) were present in preadipocytes; nevertheless these currents were measured in all differentiated cells (adipocytes). WAi exhibited greater macroscopic potassium currents than WAo with no apparent differences in kinetics or voltage dependence. The current density (pA µm^-2) calculated in WAi was higher than in WAo. Currents were blocked by millimolar concentrations of tetraethylammonium (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 2.5-fold the total number of cells in culture. Insulin increased the number of differentiated cells by 73.5 %. Cell proliferation and differentiation were inhibited by TEA. Proliferation was affected only by a high concentration of TEA. Inhibition of differentiation was dose dependent, with concentration for half-block similar to the IC₅₀ values to block potassium channels. These results suggest that insulin increases the density of Kv and that these channels may be necessary for the normal growth of white adipocytes in culture.