Norepinephrine-induced Ca2+waves depend on InsP3 and ryanodine receptor activation in vascular myocytes.

In rat portal vein myocytes, Ca2+ signals can be generated by inositol 1,4,5-trisphosphate (InsP3)- and ryanodine-sensitive Ca2+ release channels, which are located on the same intracellular store. Using a laser scanning confocal microscope associated with the patch-clamp technique, we showed that propagated Ca2+ waves evoked by norepinephrine (in the continuous presence of oxodipine) were completely blocked after internal application of an anti-InsP3 receptor antibody. These propagated Ca2+ waves were also reduced by ∼50% and transformed in homogenous Ca2+ responses after application of an anti-ryanodine receptor antibody or ryanodine. All-or-none Ca2+ waves obtained with increasing concentrations of norepinephrine were transformed in a dose-response relationship with a Hill coefficient close to unity after ryanodine receptor inhibition. Similar effects of the ryanodine receptor inhibition were observed on the norepinephrine- and ACh-induced Ca2+ responses in non-voltage-clamped portal vein and duodenal myocytes and on the norepinephrine-induced contraction. Taken together, these results show that ryanodine-sensitive Ca2+release channels are responsible for the fast propagation of Ca2+ responses evoked by various neurotransmitters producing InsP3in vascular and visceral myocytes.