抄録
We have previously reported that the 40 pS K channel is the most frequently observed K channel in cultured human renal proximal tubule cells under the control condition, and that the activity of this channel is maintained at least in part by the PKG-mediated phosphorylation. In this study, we examined whether a well-known activator of the cGMP/PKG pathway, nitric oxide (NO), would be involved in the regulation of this K channel, using the patch-clamp technique. In cell-attached patches, a non-selective inhibitor of NO synthase (NOS), L-NAME (100 μM), reduced channel activity, which was mimicked by an nNOS- and iNOS-specific inhibitor, TRIM (100 μM). These results were supported by the data that mRNAs of nNOS and iNOS, but not eNOS were detected by RT-PCR. Furthermore, an inhibitor of soluble guanylate cyclase, ODQ (10 μM), also reduced channel activity. SNP, an NO donor, of 10 μM enhanced channel activity, which was abolished by a PKG inhibitor, KT5823 (1 μM). In contrast, SNP of a higher dose (1 mM) suppressed channel activity, which was not restored by 8Br-cGMP (100 μM). Membrane potential recorded with the slow whole-cell configuration showed that L-NAME depolarized the cells by 10 mV whereas a low dose of SNP hyperpolarized by 7 mV. In conclusion, the endogenous NO produced by nNOS and/or iNOS in these cells would contribute to the maintenance of basal activity of this K channel and hence the potential formation via a cGMP/PKG-dependent mechanism, while a high dose of NO impaired channel activity independent of cGMP/PKG. [Jpn J Physiol 54 Suppl:S67 (2004)]
