Abstract
KEY POINTS: In the bladder suburothelial microvasculature, pericytes in different microvascular segments develop spontaneous Ca(2+) transients with or without associated constrictions. Spontaneous Ca(2+) transients in pericytes of all microvascular segments primarily rely on the cycles of Ca(2+) uptake and release by the sarco- and endoplasmic reticulum. The synchrony of spontaneous Ca(2+) transients in capillary pericytes exclusively relies on the spread of depolarizations resulting from the opening of Ca(2+) -activated chloride channels (CaCCs) via gap junctions. CaCC-dependent depolarizations further activate L-type voltage-dependent Ca(2+) channels as required for the synchrony of Ca(2+) transients in pericytes of pre-capillary arterioles, post-capillary venules and venules. Capillary pericytes may drive spontaneous Ca(2+) transients in pericytes within the suburothelial microvascular network by sending CaCC-dependent depolarizations via gap junctions. ABSTRACT: Mural cells in the microvasculature of visceral organs develop spontaneous Ca(2+) transients. However, the mechanisms underlying the integration of these Ca(2+) transients within a microvascular unit remain to be clarified. In the present study, the origin of spontaneous Ca(2+) transients and their propagation in the bladder suburothelial microvasculature were explored. Cal-520 fluorescence Ca(2+) imaging and immunohistochemistry were carried out on mural cells using mice expressing red fluorescent protein (DsRed) under control of the NG2 promotor. NG2(+) pericytes in both pre-capillary arterioles (PCAs) and capillaries developed synchronous spontaneous Ca(2+) transients. By contrast, although NG2-DsRed also labelled arteriolar smooth muscle cells, these cells remained quiescent. Both NG2(+) pericytes in post-capillary venules (PCVs) and NG2(-) venular pericytes exhibited propagated Ca(2+) transients. L-type voltage-dependent Ca(2+) channel (LVDCC) blockade with nifedipine prevented Ca(2+) transients or disrupted their synchrony in PCA, PCV and venular pericytes without dis-synchronizing Ca(2+) transients in capillary pericytes. Blockade of gap junctions with carbenoxolone or Ca(2+) -activated chloride channels (CaCCs) with 4,4'-diisothiocyanato-2,2'-stilbenedisulphonic acid disodium salt prevented Ca(2+) transients in PCA and venular pericytes and disrupted the synchrony of Ca(2+) transients in capillary and PCV pericytes. Spontaneous Ca(2+) transients in pericytes of all microvascular segments were abolished or suppressed by cyclopiazonic acid, caffeine or tetracaine. The synchrony of Ca(2+) transients in capillary pericytes arising from spontaneous Ca(2+) release from the sarco- and endoplasmic reticulum appears to rely exclusively on CaCC activation, whereas subsequent LVDCC activation is required for the synchrony of Ca(2+) transients in pericytes of other microvascular segments. Capillary pericytes may drive spontaneous activity in the suburothelial microvascular unit to facilitate capillary perfusion.