Comparative studies of the maxi-K (K_Ca) channel in freshly isolated myocytes of human and rat corpora

Abstract

Patch clamp techniques in freshly isolated myocytes from human corpora have documented that the large conductance calcium-sensitive K channel (K_Ca) 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 K_Ca 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 K_Ca 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 α₁-adrenergic receptor subtype by phenylephrine (PE). Large conductance K⁺ currents commensurate with the presence of the K_Ca 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 K_Ca 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 K_Ca channel has many similarities to its counterpart in the human penis.