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Articles in PresS, published online ahead of print June 4, 2002
Am J Physiol Renal Physiol, 10.1152/ajprenal.00023.2002
Submitted on January 17, 2002
Accepted on December 31, 1969
1 Department of Physiology II, Iwate Medical University, Morioka, Iwate, Japan
* To whom correspondence should be addressed. E-mail: mkubokaw{at}iwate-med.ac.jp.
An ATP-regulated inwardly rectifying K+ channel, whose activity is enhanced by protein kinase A (PKA), is present in the plasma membrane of cultured human proximal tubule cells. In this study, we investigated the effects of protein kinase G (PKG) on this K+ channel, using the patch-clamp technique. In cell-attached patches, bath application of a membrane-permeant cGMP analog, 8Br-cGMP (100 µM), stimulated channel activity, whereas application of a PKG-specific inhibitor, KT5823 (1 µM), reduced the activity. Channel activation induced by 8Br-cGMP was observed even in the presence of a PKA-specific inhibitor, KT5720 (500 nM), which was abolished by KT5823. Direct effects of cGMP and PKG were examined with inside-out patches in the presence of 1 mM MgATP. Although cytoplasmic cGMP (100 µM) alone had little effect on channel activity, subsequent addition of PKG (500 U/ml) enhanced it. Furthermore, bath application of atrial natriuretic peptide (ANP, 20 nM) in cell-attached patches stimulated channel activity, which was blocked by KT5823. In conclusion, cGMP/PKG-dependent processes participate in activating the ATP-regulated K+ channel and producing the stimulatory effect of ANP on channel activity.
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