Role of intracellular Ca2+ stores in smooth muscle of human penile erectile tissue

Objective: In human erectile tissue smooth muscle contraction and detumescence are highly dependent on an increase in cytosolic [Ca2+]. The Ca2+ influx can be derived from the extracellular space or from intracellular sarcoplasmic stores. The role of both pathways was evaluated in an organ bath study on human cavernosal strips. Patients and methods: The tissue was obtained from 12 patients with chronic erectile dysfunction. The effects of Ca2+-free solution, ryanodine, caffeine and of nifedipine on electrically and adrenergically induced contractions were evaluated. Results: Following an incubation period of 10 min in Ca2+-free solution the electrically induced contraction was reduced to 20%, whereas the contraction induced by phenylephrine (PE) was only reduced to 64 ± 6% (mean ± SEM). Ryanodine inhibited the PE-contraction to 30 ± 6% and the additional application of caffeine or nifedipine further reduced the contraction to 11% and 8%. Conclusion: The results give evidence for a role of intracellular Ca2+-stores in human cavernosal tissue. Whether the more marked effect of ryanodine in tissue from patients with erectile failure in comparison with similar experiments in rabbit cavernosal tissue might be a sign of an increased cavernosal contractility in these patients remains to be shown in future experiments with normal erectile tissue.