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  • Title: Properties of synchronous spontaneous Ca2+ transients in the mural cells of rat rectal arterioles.
    Author: Mitsui R, Hashitani H.
    Journal: Pflugers Arch; 2017 Sep; 469(9):1189-1202. PubMed ID: 28429070.
    Abstract:
    Synchrony of spontaneous Ca2+ transients among venular mural cells (smooth muscle cells and pericytes) in visceral organs relies on the intercellular spread of L-type voltage-dependent Ca2+ channel (LVDCC)-dependent depolarisations. However, the mechanisms underlying the synchrony of spontaneous Ca2+ transients between arteriolar mural cells are less understood. The spontaneous intracellular Ca2+ dynamics of arteriolar mural cells in the rat rectal submucosa were visualised by Cal-520 Ca2+ imaging to analyse their synchrony. The mural cells in fine arterioles that had a rounded cell body with several extended processes developed spontaneous 'synchronous' Ca2+ transients arising from Ca2+ released from sarcoendoplasmic reticulum Ca2+ stores. Gap junction blockers (3 μM carbenoxolone, 10 μM 18β-glycyrrhetinic acid), a Ca2+-activated Cl- channel (CaCC) blocker (100 μM 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) or lowering extracellular Cl- concentration (from 134.4 to 12.4 mM) disrupted the synchrony of Ca2+ transients between arteriolar mural cells. Blockers of T-type voltage-dependent Ca2+ channels (TVDCCs, 1 μM mibefradil or ML218) or LVDCCs (1 μM nifedipine) reduced the Ca2+ transient frequency or their area under curve (AUC), respectively. However, neither TVDCC nor LVDCC blockers disrupted the synchrony of Ca2+ transients among arteriolar mural cells. This is in contrast with rectal venules in which nifedipine disrupted the synchrony of spontaneous Ca2+ transients. Thus, spontaneous transient depolarisations arising from the opening of CaCCs may effectively spread to neighbouring arteriolar mural cells via gap junctions to maintain the Ca2+ transient synchrony. Activation of TVDCCs appears to accelerate spontaneous Ca2+ transients, while LVDCCs predominantly contribute to the duration of Ca2+ transients.
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