The Ca2+-sensitive K+ channel (maxi-K+) is an important modulator of corporal smooth muscle tone. The goal of these studies was twofold: 1) to determine the feasibility of transfecting corporal smooth muscle cells in vivo with the hSlo cDNA, which encodes for the human smooth muscle maxi-K+channel, and 2) to determine whether transfection of the maxi-K+channel would affect the physiological response to cavernous nerve stimulation in a rat model in vivo. Intracorporal microinjection of pCMVβ/Lac Z DNA in 10-wk-old rats resulted in significant incorporation and expression of β-galactosidase activity in 10 of 12 injected animals for up to 75 days postinjection. Moreover, electrical stimulation of the cavernous nerve revealed that, relative to the responses obtained in age-matched control animals ( N = 12), intracavernous injection of naked pcDNA/ hSlo DNA was associated with a statistically significant elevation in the mean amplitude of the intracavernous pressure response at all levels of current stimulation (range 0.5–10 mA) at both 1 mo ( N= 5) and 2 mo ( N = 8) postinjection. Furthermore, qualitatively similar observations were made at 3 mo ( N = 2) and 4 mo ( N = 2) postinjection. These data indicate that naked hSlo DNA is quite easily incorporated into corporal smooth muscle and, furthermore, that expression is sustained for at least 2 mo in corporal smooth muscle cells in vivo. Finally, after expression, hSlo is capable of measurably altering nerve-stimulated penile erection. Taken together, these data provide compelling evidence for the potential utility of gene therapy in the treatment of erectile dysfunction.

1 The pathophysiology of impotence related to vascular smooth muscle dysfunction in the male corpus cavernosum was studied on human isolated erectile tissue (HET). Studies were conducted on 140 sections of HET obtained from 38 male patients undergoing surgery for implantation of penile prostheses to correct underlying erectile dysfunction. 2 Spontaneous myotonic oscillations were characteristic of greater than 90% of all HET preparations at 37°C. These spontaneous oscillations were markedly attenuated by indomethacin, BW755C, nifedipine, removal of extracellular Ca2+, or lower temperatures (< 320C), but were not sensitive to inhibition by atropine, phentolamine or tetrodotoxin. Our data suggest that the oscillations may, at least in part, result from the generation and/or release of a stable cyclo-oxygenase product and a consequent increase in transmembrane Ca2 + influx. 3 The phenylephrine-induced contractions in HET may be reliably assayed up to 24 h after surgical removal, without significant alterations in the EC50, maximum response (E,,^x) or slope index of the steady-state concentration-response curve to phenylephrine. 4 The competitive and surmountable nature of the antagonism of phenylephrine-induced contractions by prazosin and yohimbine allowed calculation of antagonist dissociation constants. The calculated pKb values for prazosin and yohimbine, respectively, were 9.47 + 0.49 and 5.54 + 0.22. The rank order of agonist potency in HET was: noradrenaline = phenylephrine > clonidine. These data indicate the presence of a population of membrane receptors that are predominantly of the a,-adrenoceptor subtype.5 The entire patient population was stratified on a decennial basis into five age groups, and each age group was subsequently subdivided into diabetic and nondiabetic diagnostic categories. With respect to the steady-state phenylephrine concentration-response curves, a Winer two-factor analysis of variance revealed a significant effect of age on the calculated pEC50 value, as well as a significant age-diagnosis interaction. A post hoc statistical analysis for unpaired samples yielded significant differences between pEC50 values for diabetic and nondiabetic patients in age groups 41-50 and 61-70 years. In addition, aWiner two-factor analysis of variance also detected a significant effect of age on the calculated E.., value. 6 In conclusion, our studies demonstrate that spontaneous contractions in HET are likely to be mediated by the generation and release of a stable cyclo-oxygenase product. Furthermore, the results of both agonist and antagonist studies are consistent with the presence of a homogeneous ax-adrenoceptor population. Lastly, the responsiveness of isolated HET to phenylephrine was shown to be altered by both age and disease.

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