Prostaglandin E 1 activates the large-conductance K Ca channel in human corporal smooth muscle cells SW Lee 1 , H-Z Wang 2 , W Zhao 2 , P Ney 4 , PR Brink 5 and GJ Christ 2,3 * 1 Department of Urology, Sungkyunkwan University, College of Medicine, #50, Ilwon-Dong Kangnam-Ku, Seoul, Korea, 135 – 710; 2 Departments of Urology and 3 Physiology & Biophysics, Albert Einstein College of Medicine, Bronx, New York, 10461, USA; 4 Department of Pharmacology, Schwarz Pharma AG, Monheim, Germany; and 5 Department of Physiology and Biophysics, Health Sciences Center, State University of New York at Stony Brook, Stony Brook, New York, 11797, USA 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  2.1 mV (n  8) and 7 34  4mV (n  8), respectively. In the attached-patch configuration, the corresponding single-channel slope conductance values for the K Ca channel subtype were 173  4pS (n  8) in cultured cells, and 190  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 cell- recording mode, statistically significant, 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 confirm 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. Keywords: corporal smooth muscle; large-conductance K Ca channels; maxi-K channel; PGE 1 ; PGE 1 - a-cd; relaxation; hyperpolarization; erection Introduction Relaxation of the specialized vascular tissue of the human penis, that is, the corpus cavernosum smooth muscle, is an absolute prerequisite to penile erection. 1–3 Over the past two decades this fact has served to focus basic research efforts on elucidating the factors that regulate the contractile status of the corporal smooth muscle cell. Not surprisingly, as documented in numerous other smooth muscle cell types, 4–7 studies both in vitro and in vivo have indicated that K channels play an important physio- logical role in the tonically contracted smooth muscle of the human corpus cavernosum. 8 – 10 While there is evidence for the presence of at least four subtypes of K channels in human corporal smooth muscle cells, the large conductance cal- cium-sensitive potassium channel (maxi-K or K Ca channel) and the metabolically regulated potassium channel (K ATP ) are clearly the most physiologically relevant. 8 – 10 The latter is the putative target of the K channel modulators that have been documented to relax corporal smooth muscle both in vitro and in vivo, while the former is thought to play a more dynamic role in regulating intracellular calcium levels, and thus, corporal smooth muscle tone and erectile capacity. 2,3 It is precisely because contin- uous transmembrane calcium flux through voltage- dependent calcium channels is essential to the maintenance and modulation of corporal smooth muscle contraction that K channels, 11 – 14 and the *Correspondence: Dr GJ Christ, Laboratory of Molecular & Integrative Urology, Room 744, Forchheimer Building, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA. Received 10 December 1998; revised 7 Janauary 1999; accepted 14 Janauary 1999 International Journal of Impotence Research (1999) 11, 189–200 ß 1999 Stockton Press All rights reserved 0955-9930/99 $15.00 http://www.stockton-press.co.uk/ijir