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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.

We previously showed that corpus cavernosum smooth muscle cells are connected via gap junctions in situ and in culture and that a major protein component of these gap junctions is connexin43. To characterize the physiological properties of the gap junctions between corpus cavernosum smooth muscle cells, we now demonstrate that the cells are dye and electrically coupled and describe some of the gating properties of these gap junctional channels at macroscopic and single-channel levels. Junctional conductance (gj) between corporal smooth muscle cells was moderately voltage sensitive; was reduced rapidly, reversibly, and completely by halothane; and was increased by treatment with a tumor-promoting phorbol ester [12-O-tetradecanoylphorbol-13-acetate (TPA)] and decreased by isoproterenol. Histograms of unitary junctional currents revealed multiple conductance peaks with events of approximately 90 pS being the most abundant. TPA and phenylephrine produced large increases in relative frequencies of the smaller events, whereas isoproterenol and 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) slightly increased the relative frequencies of the larger events. None of the tested drugs substantially affected the steady-state voltage dependence of gj. These second messenger systems also affected expression of connexin43 by corpus cavernosum smooth muscle cells, as judged by immunoblots. At 6 h of treatment, both TPA- and 8-BrcAMP-treated cultures showed markedly elevated levels of connexin43, whereas at 24 h, the level of connexin43 in TPA-treated cultures had returned to control levels. Together, these data indicate that second messenger molecules involved in penile erection produce changes in gap junction expression and function; it is plausible that these changes could be physiologically relevant in altering and propagating changes in vasomotor tone.

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