INHIBITION BY P1075 AND PINACIDIL OF A CALCIUM-INDEPENDENT CHLORIDE CONDUCTANCE IN CONDITIONALLY-IMMORTAL RENAL GLOMERULAR MESANGIAL CELLS

1 Depolarization of mesangial cells has been shown to occur following an outward movement of chloride ions from the cell. We have shown prev iously that mesangial cells from the H-2K(b)-tsA58 transgenic mouse po ssess a significant whole-eel chloride conductance and consequently ar e a suitable preparation for the study of potential chloride channel i nhibitors. 2 The effects on the whole-cell chloride conductance of the chloride channel inhibitor, 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) and the potassium channel openers, (KCOs) P1075 and pinacidil w ere investigated in mesangial cells from the N-2K(b)-tsA58 transgenic mouse cultured in permissive conditions (at 33 degrees C in the presen ce of 50 u ml(-1) murine gamma-interferon). 3 In symmetrical solutions of 140 mM tetramethylammonium chloride (TMACl) the whole-cell chlorid e conductance was 1.08 +/- 0.05 nS (n = 63) and this could be reversib ly inhibited by 5 x 10(-5) M NPPB. 4 Both P1075 and pinacidil inhibite d the whale-cell chloride conductance. This inhibition was not reversi ble after drug washout and was demonstrated only when drugs were appli ed to the extracellular surface of the cells. Very low concentrations of the drugs were found to reduce the chloride conductance after 16 h incubation but under no circumstances studied was the conductance tota lly inhibited, leaving a mean residual current of 0.33 +/- 0.03 nS (n = 12). 5 The effects of different peptide calcium concentrations on th e magnitude of the residual current in the presence of the drugs were investigated. The residual current was reduced with 10(-8) M calcium i n the pipette and increased with 10(-3) M pipette calcium. Therefore, these data suggest that P1075 and pinacidil selectively inhibit a calc ium-independent chloride conductance in mesangial cells from the H-2K( b)-tsA58 transgenic mouse.