Role of intracellular stores in the regulation of rhythmical [Ca2+]i changes in interstitial cells of Cajal from rabbit portal vein

Rhythmical [Ca2+]i changes persisted in nicardipine, but were abolished in Ca2+-free solution as well as by SK&F96365, cyclopiazonic acid, thapsigargin, 2-APB, xestospongin C or ryanodine. Intracellular Ca2+ stores visualised with the low-affinity Ca2+ indicator fluo-3FF were found to be enriched with ryanodine receptors (RyRs) detected with BODIPY TR-X ryanodine. Rhythmical [Ca2+]i changes originated from a perinuclear S/ER element showing the highest RyR density. Immunostaining with anti-TRPC3,6,7 antibodies revealed the expression of these channel proteins in the ICC plasmalemma. This suggests that these rhythmical [Ca2+]i changes, a key element of ICC pacemaking activity, result from S/ER Ca2+ release which is mediated via RyRs and IP3 receptors and is modulated by the activity of S/ER-Ca2+-ATPase and TRP channels but not by L-type Ca2+ channels.