Roles of endothelial prostaglandin I 2 in maintaining synchronous spontaneous Ca 2+ transients in rectal capillary pericytes.

In hollow visceral organs, capillary pericytes appear to drive spontaneous Ca 2+ transients in the upstream arterioles. Here, mechanisms underlying the intercellular synchrony of pericyte Ca 2+ transients were explored. Ca 2+ dynamics in NG2 chondroitin sulphate proteoglycan (NG2)-expressing capillary pericytes were examined using rectal mucosa-submucosa preparations of NG2-GCaMP6 mice. Spontaneous Ca 2+ transients arising from endoplasmic reticulum Ca 2+ release were synchronously developed amongst capillary pericytes in a gap junction blocker (3 μM carbenoxolone)-sensitive manner and could spread into upstream vascular segments. Spontaneous Ca 2+ transients were suppressed by the Ca 2+ -activated Cl - channel (CaCC) blocker niflumic acid and their synchrony was diminished by a TMEM16A inhibitor (3 μM Ani9) in accordance with TMEM16A immunoreactivity in pericytes. In capillaries where cyclooxygenase (COX)-2 immunoreactivity was expressed in endothelium but not pericytes, non-selective COX inhibitors (1 μM indomethacin or 10 μM diclofenac) or COX-2 inhibitor (10 μM NS 398) disrupted the synchrony of spontaneous Ca 2+ transients and raised the basal Ca 2+ level. Subsequent prostaglandin I 2 (PGI 2 ; 100 nM) or the K ATP channel opener levcromakalim restored the synchrony with a reduction in the Ca 2+ level. PGI 2 receptor antagonist (1 μM RO1138452) also disrupted the synchrony of spontaneous Ca 2+ transients and increased the basal Ca 2+ level. Subsequent levcromakalim restored the synchrony and reversed the Ca 2+ rise. Thus, the synchrony of spontaneous Ca 2+ transients in pericytes appears to be developed by the spread of spontaneous transient depolarisations arising from the opening of TMEM16A CaCCs. Endothelial PGI 2 may play a role in maintaining the synchrony, presumably by stabilising the resting membrane potential in pericytes. KEY POINTS: Capillary pericytes in the rectal mucosa generate synchronous spontaneous Ca 2+ transients that could spread into the upstream vascular segment. Spontaneous Ca 2+ release from the endoplasmic reticulum (ER) triggers the opening of Ca 2+ -activated Cl - channel TMEM16A and resultant depolarisations that spread amongst pericytes via gap junctions, establishing the synchrony of spontaneous Ca 2+ transients in pericytes. Prostaglandin I 2 (PGI 2 ), which is constitutively produced by the endothelium depending on cyclooxygenase-2, appears to prevent premature ER Ca 2+ releases in the pericytes allowing periodic, regenerative Ca 2+ releases. Endothelial PGI 2 may maintain the synchrony of pericyte activity by stabilising pericyte resting membrane potential by opening of K ATP channels.