Potassium (K) channels play a signi®cant role in modulating human corporal smooth muscle tone, and thus, erectile capacity. Recent pharmacological studies indicate that the metabolicallyregulated K channel (K ATP ) may be an important modulator of human penile erection with signi®cant therapeutic potential. The goal of these initial studies, therefore, was to utilize patch clamp techniques to characterize the putative K ATP subtype(s) present in cultured and freshly isolated human corporal smooth muscle cells. In the cell-attached patch mode, two distinct unitary K currents were identi®ed whose respective conductance values were similar in cultured and freshly isolated smooth muscle cells. In cultured myocytes, the measured conductance values in symmetric KCl (140 mM) solutions were 59.1 AE 2.7 pS and 18.4 AE 2.1 pS (n 5 cells). Under identical experimental conditions in freshly isolated myocytes, corresponding conductance values were 59.2 AE 3.7 pS and 18.5 AE 2.4 pS, respectively (n 4 cells). I-V curves constructed during step depolarization ( 7 60 to 80 mV), revealed a linear I-V relationship for both unitary conductances. Single channel records documented that both conductances were reversibly inhibited by the application of ATP (1 ± 3 mM) to the bath solution in the inside-out attached patch con®guration. The unitary activity of both K channel subtypes was signi®cantly increased by the application of pinacidil (10 mM) and levcromakalim (10 mM). Whole cell patch recordings documented a glibenclamide-sensitive, pinacidil-and levcromakalim-induced increase in the whole cell outward K current during step depolarization ( 7 70 mV to 130 mV) of 105 AE 37%, 139 AE 42%, respectively. These data con®rm and extend our previous observations, and provide the ®rst evidence for the presence of K ATP channel subtypes in human corporal smooth muscle cells.

The large conductance calcium-sensitive potassium channel (K Ca or maxi-K) is an important modulator of human corporal smooth muscle tone, and therefore, erectile capacity. The goal of this investigation was to evaluate the actions of prostaglandin E 1 (PGE 1 ), the most widely used and effective drug for the treatment of impotence, on the activity of the K Ca channel, a prominent K current present in human corporal smooth muscle. Whole-cell patch clamp studies conducted on short-term cultured and enzymatically dissociated human corporal smooth muscle cells, revealed mean resting potentials of 7 50.8 AE 2.1 mV (n 8) and 7 34 AE 4 mV (n 8), respectively. In the attached-patch con®guration, the corresponding single-channel slope conductance values for the K Ca channel subtype were 173 AE 4 pS (n 8) in cultured cells, and 190 AE 13 pS (n 3) in freshly isolated myocytes. Furthermore, voltage clamp experiments revealed that relative to control values, the application of PGE 1 to cultured cells (3.3 or 33 mM) elicited an apparent increase in both the open probability (P o ; ranging from 1.2 ± 23 fold), and the mean open time (5 ± 6 fold) of the K Ca channel at membrane potentials of 90 mV and 110 mV. PGE 1 -induced alterations in K Ca channel activity were also observed in freshly isolated corporal myocytes. In the whole cellrecording mode, statistically signi®cant, Charybdotoxin-sensitive (100 nM) 2 ± 3 fold increases in the outward K currents were observed in both cultured and freshly isolated corporal myocytes. The presence of a PKA inhibitor (fragment 6 ± 22 amide; 10 mM) in the pipette tip was also associated with a nearly complete ablation of the observed PGE 1 -induced whole cell K currents. Taken together, these data con®rm and extend our previous observations, and indicate that PGE 1 -induced relaxation of human corporal smooth muscle is related, at least in part, to activation of the K Ca channel subtype resulting in cellular hyperpolarization.

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 a 1 -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-bromocAMP 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 con®rm 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.

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