February 2000, Volume 12, Issue 1, Pages 9 - 18

Paper

Comparative studies of the maxi-K (KCa) channel in freshly isolated myocytes of human and rat corpora H-Z Wang1, SW Lee1 & GJ Christ1,2 1Department of Urology, Albert Einstein College of Medicine, Bronx, New York     2Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York, USA     Correspondence to: Dr GJ Christ, Institute for Smooth Muscle Biology, Laboratory of Molecular & Integrative Urology, Room 744, Forchheimer Building, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA.

Keywords

corporal smooth muscle;   large-conductance KCa channels;   maxi-K channel;   cAMP;   relaxation;   erection

Abstract

Patch clamp techniques in freshly isolated myocytes from human corpora have documented that the large conductance calcium-sensitive K channel (KCa) subtype represents an important convergence point for the modulation of corporal smooth muscle tone, and therefore, erectile capacity. Other recent studies indicate a similar role for the KCa channel in the modulation of smooth muscle tone in the rat penis. Therefore, the explicit aim of this investigation was to evaluate and compare the characteristics of the KCa channel subtype present in freshly isolated myocytes from rat and human corpora. In short, myocytes isolated from rat and human corpora retain their characteristic morphology and contractility in vitro, as evidenced by light microscopic studies of their respective responses to activation of the 1-adrenergic receptor subtype by phenylephrine (PE). Large conductance K+ currents commensurate with the presence of the KCa channel were readily apparent in myocytes from both preparations. I-V curves constructed from cell-attached patches utilizing symmetric KCl solutions revealed the presence of a single channel slope conductance of 200 pS for both rat and human myocytes. 1 mM TEA applied in the bath solution reversibly diminished whole cell outward K+ currents by 50%, and also blocked the unitary KCa channel activity observed in the outside-out patch mode. Addition of 2 mM 8-bromo-cAMP elicited a TEA-sensitive (1 mM) 2-3 fold increase in the magnitude of the whole cell outward K+ currents in rat myocytes. Taken together, these data confirm and extend previous observations and provide strong evidence that the rat corporal smooth muscle KCa channel has many similarities to its counterpart in the human penis. International Journal of Impotence Research (2000) 12, 9-18.

Received 28 April 1999; Accepted 2 May 1999

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