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This Article Full Text Full Text (PDF) All Versions of this Article: 296/1/F107    most recent 90440.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Teramoto, N. Articles by Cole, W. C. Search for Related Content PubMed PubMed Citation Articles by Teramoto, N. Articles by Cole, W. C.

ATP-sensitive K⁺ channels in pig urethral smooth muscle cells are heteromultimers of Kir6.1 and Kir6.2

Departments of ¹Pharmacology and ²Urology, Graduate School of Medical Sciences, Kyushu University, Fukuoka; ³Smooth Muscle Research Group and Department of Pharmacology and Therapeutics, University of Calgary, Calgary, Alberta, Canada; and ⁴Laboratory of Biosignals and Response, Graduate School of Biostudies, Kyoto University, Kyoto, Japan

Submitted 29 July 2008 ; accepted in final form 20 October 2008

The inwardly rectifying properties and molecular basis of ATP-sensitive K⁺ channels (K_ATP channels) have now been established for several cell types. However, these aspects of nonvascular smooth muscle K_ATP channels still remain to be defined. In this study, we investigated the molecular basis of the pore of K_ATP channels of pig urethral smooth muscle cells through a comparative study of the inwardly rectifying properties, conductance, and regulation by PKC of native and homo- and heteroconcatemeric recombinant Kir6.x channels coexpressed with sulfonylurea receptor subunit SUR2B in human embryonic kidney (HEK) 293 cells by the patch-clamp technique (conventional whole-cell and cell-attached modes). In conventional whole-cell clamp recordings, levcromakalim (1 µM) caused a concentration-dependent increase in current that demonstrated strong inward rectification at positive membrane potentials. In cell-attached mode, the unitary amplitude of levcromakalim-induced native and recombinant heteroconcatemeric Kir6.1-Kir6.2 K_ATP channels also showed strong inward rectification at positive membrane potentials. Phorbol 12,13-dibutyrate, but not the inactive phorbol ester, 4-phorbol 12,13-didecanoate, enhanced the activity of native and heteroconcatemeric K_ATP channels at –50 mV. The conductance of the native channels at 43 pS was consistent with that of heteroconcatemeric channels with a pore-forming subunit composition of (Kir6.1)₃-(Kir6.2). RT-PCR analysis revealed the expression of Kir6.1 and Kir6.2 transcripts in pig urethral myocytes. Our findings provide the first evidence that the predominant K_ATP channel expressed in pig urethral smooth muscle possesses a unique, heteromeric pore structure that differs from the homomeric Kir6.1 channels of vascular myocytes and is responsible for the differences in inward rectification, conductance, and PKC regulation exhibited by the channels in these smooth muscle cell types.