Many hormonal effects in eukaryotic cells are produced through changes in ionic membrane permeabilities and subsequent changes in membrane potential. Although a great deal is known concerning white fat metabolism, little information about its electrophysiology is available. We developed an experimental model that allowed us to obtain mature white adipocytes from preadipocytes of epidydimal tissue of rat (Ramírez-Ponce et al. 1996). In these cells we demonstrated the existence of voltage-dependent K⁺ channels (Kv), using the whole-cell variant of the patch-clamp technique.

To date, there are no electrophysiological data referring to human white adipocytes, and only indirect studies have suggested the existence of ionic channels in these cells. In metabolic studies, it is common to find distinct properties and regulatory mechanisms between different cell models derived from diverse species and development stage. For this reason, it would be interesting to know if human adipocytes have ionic channels, and if these have the same properties as the channels of rat adipocytes. This fact will increase interest in the electrophysiology of white adipose tissue and its possible physiological importance.

In this study, the whole-cell voltage-clamp method was used to study the membrane electrical properties of human adipocytes cells obtained by differentiation from precursors of human abdominal and mammary tissues. Subcutaneous and visceral samples of human fat were obtained from normal-weight subjects (< 27 kg m^-2) undergoing abdominal surgery or surgical mammary reduction. Patients with malignant or chronic inflammation diseases were excluded. The study was approved by the Ethics Committee of the Hospital Virgen Macarena de Sevilla. All differentiated cells exhibited outward currents with a sigmoidal activation kinetic. The outward currents showed activation thresholds between -20 and -30 mV and a slow inactivation. The ionic channels underlying the macroscopic current were highly selective for K⁺. Their selectivity was typical for K⁺ channels with relative permeabilities of K⁺ > NH₄⁺ > Cs⁺ > Na⁺. There was no evidence of any other type of voltage-gated channel. The potassium currents were blocked reversibly by tetraethylammonium and barium. The IC₅₀ values and Hill coefficient of tetraethylammonium inhibition of I_KV were 0.56 mM and 1.17 respectively. These results demonstrate that human adipose cells have voltage-dependent potassium currents.