cGMP serves as an extracellular regulator of a Ca2+-dependent K+ channel in immortalized human proximal tubule cells

Recently we showed that a K+ channel in immortalized human kidney epithelia l (IHKE-1) cells derived from the proximal tubule is regulated by natriuret ic peptides in cell-attached patches and directly regulated by cGMP in exci sed inside-out oriented membrane patches [1], The patch clamp technique was used to investigate the regulatory effect of extracellular, nonmembrane pe rmeable cGMP on membrane voltage and the regulation of this K+ channel in o utside-out oriented membrane patches. In 7 out of 7 experiments the membran e voltage of IHKE-1 cells depolarized by 3.9 +/- 0.1 mV when the non-membra ne permeable cGMP was added to the bath solution. In outside-out oriented m embrane patches cGMP inhibited P already at 1 muM (-12 +/- 4%, n=7), at 0.1 mM inhibition of P reached -39 +/- 6% (n=14). cAMP (0.1 mM) only had Da we ak inhibitory effect (n=7). GTP and ATP (n=7 each) had no significant effec t on P-o from the outside. When cGMP was added to the pipette solution in e xperiments with outside-out oriented membranes cGMP still inhibited this K channel from the outside by 36 +/- 6% (n=6). In 4 paired experiments 8-Br- cGMP (0.1 mM) showed a significantly higher inhibitory effect on P-o compar ed to cGMP (0.1 mM). cGMP inhibits a K+ channel in human proximal tubule ce lls from the outside and may serve as an autocrine and paracrine regulatory factor in the kidney. Copyright (C) 2001 S. Karger AG, Basel.