Integrative erectile biology: The effects of age and disease on gap junctions and ion channels and their potential value to the treatment of erectile dysfunction

Initiation, maintenance, and modulation of corporal smooth muscle tone are critically dependent upon agonist-induced changes in intracellular calcium levels and mobilization as well as transmembrane calcium flux. The transient control of myocyte excitability and contractility at the cellular level is inextricably linked to membrane potenial, which, in turn, is modulated by potassium ion efflux through one of the four known corporeal smooth muscle potassium ion channels. Corporal tissue responses are subsequently coordinated by means of the movement of intracellular second messenger molecules (i.e., IP₃, cAMP, cGMP) and ions (i.e., K⁺ and Ca²⁺) among the corporal myocytes by means of intracellular communication through gap junction channels. Knowledge of the critical contribution of these interlinking cellular (nonjunctional ion channels [e.g., maxi-K]) and tissue (gap junction channels [e.g., connexin 43]) systems to the modulation of erectile capacity has provided the scientific rationale for the promulgation of the successful preclinical testing of hSlo ion channel gene therapy for the normalization of erectile status in both aged and diabetic rats.