Potassium conductances and proliferation in conditionally immortalized renal glomerular mesangial cells from the H-2K(b)-tsA58 transgenic mouse

The effects of the temperature-sensitive, immortalizing Simian Virus 40 T antigen, tsA58, on whole-cell potassium conductances were assessed in renal gomerular mesangial cells from H-2K(b)-tsA58 transgenic mice [1]. MTT cell viability assay data indicated that in permissive (33 degrees C, 50 U mi(-1) gamma-interferon, IFN +) and non-permissive (37 degrees C, without gamma-interferon, IFN -) culture conditions the oncogene was active and inactive respectively. In IFN + cells whole-cell currents were inhibited by 10 mM 4-aminopyridine, 1 mM ATP and glibenclamide (glyburide, IC50 = 0.4 mu M) and stimulated by cromakalim (EC(50) = 40 mu M). Furthermore, increases in pipette free calcium activity stimulated the potassium conductance (EC(50) = 0.5 mu M). Apamin inhibited this conductance (IC50 = 9 nM). None of these effects were observed in IFN - cells. The potassium conductance in IFN - cells was activated by a hyposmotic shock and this was inhibited by Gd3+. These data indicate that (1) conductances consistent with ATP-sensitive and small, calcium-activated potassium channels art: found in IFN + cells, (2) an osmotically-sensitive channel is found in IFN - cells and (3) channel expression is dependent upon the activation of tsA58.