Cl^- channels in basolateral renal medullary membrane vesicles: IV. Analogous channel activation by Cl^- or cAMP-dependent protein kinase

We examined the interactions of cAMP-dependent protein kinase and varying aqueous Cl^- concentrations in modulating the activity of Cl^- channels obtained by fusing basolaterally enriched renal outer medullary vesicles into planar lipid bilayers. Under the present experimental conditions, the cis and trans solutions face the extracellular and intracellular aspects of these Cl^- channels, respectively. Raising the trans Cl^- concentration from 2 to 50 mm increased the channel open-time probability, raised the unit channel conductance, and affected the voltage-independent determinant (ΔG) of channel activity but not the gating charge (Winters, C.J., Reeves, W.B., Andreoli, T.E. 1990. J. Membrane Biol.118:269-278). With 2 mmtrans KCl, trans addition of the catalytic subunit of PKA (C-PKA) plus ATP increased channel open-time probability and altered the voltage-independent determinant of channel activity without affecting either unit channel conductance or gating charge. The effect was ATP specific, did not occur with (C-PKA plus ATP) addition to cis solutions, and was abolished by denaturing C-PKA. Finally, (C-PKA plus ATP) activation of channel activity was not detected with relatively high (50 mm)trans Cl^- concentrations. These data indicate that (C-PKA plus ATP) might modulate Cl^- channel activity by phosphorylation at or near the Cl^--sensitive site on the intracellular face of these channels.