cGMP serves as an extracellular regulator of a Ca(2+)-dependent K(+) channel in immortalized human proximal tubule cells.
Recently we showed that a K(+) channel in immortalized human kidney epithelial (IHKE-1) cells derived from the proximal tubule is regulated by natriuretic peptides in cell-attached patches and directly regulated by cGMP in excised inside-out oriented membrane patches [1]. The patch clamp technique was used to investigate the regulatory effect of extracellular, non-membrane permeable cGMP on membrane voltage and the regulation of this K(+) channel in outside-out oriented membrane patches. In 7 out of 7 experiments the membrane voltage of IHKE-1 cells depolarized by 3.9 +/- 0.1 mV when the non-membrane permeable cGMP was added to the bath solution. In outside-out oriented membrane patches cGMP inhibited P(o) already at 1 microM (-12 +/- 4%, n=7), at 0.1 mM inhibition of P(o) reached -39 +/- 6% (n=14). cAMP (0.1 mM) only had a weak inhibitory effect (n=7). GTP and ATP (n=7 each) had no significant effect on P(o) from the outside. When cGMP was added to the pipette solution in experiments 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) compared to cGMP (0.1 mM). cGMP inhibits a K(+) channel in human proximal tubule cells from the outside and may serve as an autocrine and paracrine regulatory factor in the kidney.
Westfälische Wilhelms-Universität Münster, Medizinische Poliklinik, Experimentelle Nephrologie, Münster, Germany. hirschi@uni-muenster.de
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Hirsch
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Weber
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Schlatter
D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000008:administration & dosage / Q000378:metabolism*; D015536:Down-Regulation; D004847:Epithelial Cells / Q000378:metabolism; D005110:Extracellular Space; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000378:metabolism*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D006152:Cyclic GMP; D002118:Calcium