Evidence for signaling via gap junctions from smooth muscle to endothelial cells in rat mesenteric arteries: possible implication of a second messenger

Enhanced spontaneous Ca2+ events in endothelial cells reflect signalling through myoendothelial gap junctions in pressurized mesenteric arteries

“…Importantly, and in contrast to another report in the same tissue [37], we used concentrations of PE that did not stimulate vasomotion, and therefore only observed asynchronous Ca 2+ events that likely did not rely on cell-cell coupling, supporting a lack of non-specific actions of carbenoxolone on smooth muscle Ca 2+ events. A similar imaging approach has been used previously [37], but the authors were able to carefully load a different Ca 2+ -sensitive dye into each cell type and enabled simultaneous Ca 2+ imaging in endothelial and smooth muscle cells. That study fully supports our data that both KCl and PE increase endothelial cell Ca 2+ levels, and showed that another gap junction uncoupler, palmitoleic acid, inhibited the rise in endothelial cell Ca 2+ levels, and in the case of KCl, did not affect the response in smooth muscle cells [37].…”

“…Ca 2+ and IP 3 are, however, interdependent in terms of their regenerative process [54]. Indeed, the ability of KCl to evoke rises in endothelial cell Ca 2+ appears dependent on phospholipase C and IP 3 -induced Ca 2+ release [37], supporting an important role for this signalling pathway in rat mesenteric arteries. Therefore, in order to define the relative importance of each signal, a specific and effective cell-permeant inhibitor targeted to IP 3 receptors or the selective loading of specific inhibitory IP 3 receptor antibodies into endothelial cells are called for.…”

“…The selective · 1 agonist PE, stimulates direct smooth muscle depolarization and contraction in the rat mesenteric artery, it has no direct action on the endothelial cells [16,17,37]. So both KCl and PE would be expected to depolarize endothelial cells, either directly or indirectly via smooth muscle cells [38].…”

“…A similar imaging approach has been used previously [37], but the authors were able to carefully load a different Ca 2+ -sensitive dye into each cell type and enabled simultaneous Ca 2+ imaging in endothelial and smooth muscle cells. That study fully supports our data that both KCl and PE increase endothelial cell Ca 2+ levels, and showed that another gap junction uncoupler, palmitoleic acid, inhibited the rise in endothelial cell Ca 2+ levels, and in the case of KCl, did not affect the response in smooth muscle cells [37]. Further support of an influence from the muscle layers via gap junctions comes from our use of nifedipine, which decreases [Ca 2+ ] i by inhibiting voltage-gated Ca 2+ channels in smooth muscle cells, and significantly inhibited Ca 2+ events in endothelial cells.…”

“…Overall, these separate lines of evidence from pressurized mesenteric arteries strongly support the suggestion that regulation of Ca 2+ events within endothelial cells by the adjacent smooth muscle cells is affected through gap junctions, even under resting conditions. Among the potential candidates for Ca 2+ signalling through myoendothelial gap junctions are IP 3 and Ca 2+ [15,37,51,52]. The exact contribution possible by Ca 2+ and IP 3 passing through gap junctions remains to be defined.…”