Uhrenholt TR, Domeier TL, Segal SS. Propagation of calcium waves along endothelium of hamster feed arteries. An increase in tissue blood flow requires relaxation of smooth muscle cells along entire branches of the resistance vasculature. Whereas the spread of hyperpolarization along the endothelium can coordinate smooth muscle cell relaxation, complementary signaling events have been implicated in the conduction of vasodilation. We tested the hypothesis that Ca 2ϩ waves propagate from cell to

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... ll along the endothelium of feed arteries exhibiting spontaneous vasomotor tone. Feed arteries of the hamster retractor muscle were isolated, pressurized to 75 mmHg at 37°C, and developed myogenic tone spontaneously. Smooth muscle cells and endothelial cells were loaded with the Ca 2ϩ indicator Fluo-4. An acetylcholine stimulus was delivered locally using microiontophoresis (1-m pipette tip, 1 A, 1 s), and Ca 2ϩ signaling within and along respective cell layers was determined using laser-scanning confocal microscopy. Acetylcholine triggered an increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ]i) of endothelial cells at the site of stimulation that preceded two distinct events: 1) a rapid synchronous decrease in smooth muscle [Ca 2ϩ ]i along the entire vessel and 2) an ensuing Ca 2ϩ wave that propagated bidirectionally along the endothelium at ϳ111 m/s for distances exceeding 1 mm. Maximal dilation of vessels with either nifedipine (1 M) or sodium nitroprusside (SNP, 100 M) reduced the distance that Ca 2ϩ waves traveled to ϳ300 m (P Ͻ 0.05). Thus Ca 2ϩ waves propagate along the endothelium of resistance vessels with vasomotor tone, and this signaling pathway is compromised during maximal dilation with nifedipine or SNP.