Ryanodine-sensitive intracellular Ca2+ stores in isolated rabbit penile erectile tissue

Norepinephrine release from adrenergic nerve terminals leads to a rise in intracellular Ca2+, which promotes penile smooth muscle contraction and detumescence. Ca2+ sources are the extracellular space and sarcoplasmic Ca2+ stores. To elucidate the role of intracellular stores strips from rabbit erectile tissue were investigated in an organ bath study. Contractions were elicited by phenylephrine (PE) and electrical stimulation. Incubation in Ca(2+)-free solution as well as exposure to nifedipine did not abolish electrical or PE-induced contraction. Ryanodine (10(-5) mol/l), a functional blocker of sarcoplasmic Ca2+ channels, significantly reduced PE response. In the presence of caffeine (10(-3) mol/l) the effect was significantly enhanced. Addition of nifedipine nearly abolished the contraction. These results provide evidence for intracellular Ca2+ pools in cavernosal tissue and indicate that the alpha 1-adrenoceptor-induced contraction requires the opening of voltage-gated Ca2+ channels and the release of Ca2+ from intracellular stores.