The "syncytial tissue triad": a model for understanding how gap junctions participate in the local control of penile erection.

Recent findings from both clinical and experimental studies document the importance of syncytial relaxation and contraction of corporal smooth muscle to penile erection and detumescence, respectively. However, the mechanism(s) permitting coordinated response generation among the vast array of largely inexcitable corporal smooth muscle cells is unclear. In this report the compelling evidence for a major role of intercellular communication through gap junctions to erectile function is reviewed. Moreover, a novel concept is advanced to explain more fully the putative mechanistic basis for integrative erectile tissue biology. Specifically, the presence of gap junctions, in concert with the autonomic nervous system and myogenic intracellular signal transduction mechanisms, is postulated to form a "syncytial tissue triad" that is largely responsible for the local modulation of corporal smooth muscle tone. It is reasonable to assume that the existence of this "syncytial tissue triad" confers a plasticity, adaptability, and flexibility to erectile function that may well account for the observed diversity of mechanisms known to regulate penile erection as well as the multifaceted etiology of erectile dysfunction.