The presynaptic release of norepinephrine leads to a rise in cytosolic
Ca2+ and promotes contraction of the cavernous smooth muscle. Ca2+ de
rives from the extracellular space and sarcoplasmic stores. The import
ance of intracellular stores was investigated in an organ bath study u
sing tissue strips of rabbit cavernous muscle, Contractions were induc
ed by phenylephrine and electrical stimulation. After incubation in Ca
2+-free solution as well as after administration of nifedipine till co
ntractile responses were encountered. Ryanodine, a functional blocker
of intracellular Ca2+-channels, significantly inhibited contractions a
nd caffeine pronounced this effect. Rabbit cavernous smooth muscle con
traction seems to involve an influx of Ca2+-ions from the extracelluar
space and sarcoplasmic Ca2+-stores.