Gap junctions between human corpus cavernosum smooth muscle cells: Gating properties and unitary conductance

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 (g(j)) 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 ~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-Br-cAMP) slightly increased the relative frequencies of the larger events. None of the tested drugs substantially affected the steady-state voltage dependence of g(j). 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.