Blockers of voltage-gated K channels inhibit proliferation of cultured brown fat cells

Cultured brown fat cells have both voltage- and Ca(2+)-activated potassium channels. We tested whether potassium channel activity is necessary for brown fat proliferation by growing adipocytes and preadipocytes from neonatal rat brown fat in the presence of potassium channel blockers. Whole cell patch-clamp experiments showed that verapamil, nifedipine, and quinine block the voltage-gated potassium current (IK,V) with micromolar affinity. Ca(2+)-activated currents (IK,NE) could be activated by micromolar intracellular Ca2+ concentrations and were blocked by nanomolar concentrations of apamin. Both IK,V and IK,NE are blocked by millimolar concentrations of tetraethylammonium (TEA). Under standard culture conditions, the number of cells showing the multilocular morphology characteristic of brown fat cells doubled in 3-5 days. Continuous exposure to 100 nM norepinephrine had no effect on this process. Cell proliferation was inhibited by TEA, quinine, or verapamil. The inhibition was dose dependent, with concentrations for half-block of cell proliferation similar to the Kd values for block of IK,V. Apamin, which selectively blocks IK,NE, had no effect on cell growth. These results suggest that functional voltage-gated potassium channels, but not Ca(2+)-activated potassium channels, may be necessary for the normal proliferation of brown fat cells in culture.