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

Teramoto N, Zhu H, Shibata A, Aishima M, Walsh EJ, Nagao M, Cole WC. ATP-sensitive K+ channels in pig urethral smooth muscle cells are heteromultimers of Kir6.1 and Kir6.2. Am J Physiol Renal Physiol 296: F107-F117, 2009. First published October 22, 2008; doi: 10.1152/ajprenal.90440.2008.-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 mu M) 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 alpha-phorbol 12,13-didecanoate, enhanced the activity of native and heteroconcatemeric K-ATP channels at -50 mV. The conductance of the native channels at similar to 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.