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

Abstract

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 Ca²⁺-free solution as well as exposure to nifedipine did not abolish electrical or PE-induced contraction. Ryanocline (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 α₁-adrenoceptor-induced contraction requires the opening of voltage-gated Ca²⁺ channels and the release of Ca²⁺ from intracellular stores.