Role of capillary pericytes in the integration of spontaneous Ca²⁺ transients in the suburothelial microvasculature in situ of the mouse bladder

Abstract

Mural cells in the microvasculature of visceral organs develop spontaneous Ca transients. However, the mechanisms underlying the integration of these Ca transients within a microvascular unit remain to be clarified. In the present study, the origin of spontaneous Ca transients and their propagation in the bladder suburothelial microvasculature were explored. Cal-520 fluorescence Ca 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 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 transients. L-type voltage-dependent Ca channel (LVDCC) blockade with nifedipine prevented Ca transients or disrupted their synchrony in PCA, PCV and venular pericytes without dis-synchronizing Ca transients in capillary pericytes. Blockade of gap junctions with carbenoxolone or Ca -activated chloride channels (CaCCs) with 4,4'-diisothiocyanato-2,2'-stilbenedisulphonic acid disodium salt prevented Ca transients in PCA and venular pericytes and disrupted the synchrony of Ca transients in capillary and PCV pericytes. Spontaneous Ca transients in pericytes of all microvascular segments were abolished or suppressed by cyclopiazonic acid, caffeine or tetracaine. The synchrony of Ca transients in capillary pericytes arising from spontaneous Ca 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 transients in pericytes of other microvascular segments. Capillary pericytes may drive spontaneous activity in the suburothelial microvascular unit to facilitate capillary perfusion.

The three faces of pericytes

“…In this issue of The Journal of Physiology , Hashitani et al . () beautifully illustrate three different phenotypes of pericytes comprised within the suburothelial microvasculature of mouse bladder, confirming previous reports in the rat ureter microvasculature (Borysova et al . ).…”

“…In contrast, Hashitani et al . () convincingly demonstrate that NG2 positive capillary pericytes in the suburothelial vasculature do not express α‐SMA and are not contractile. These data are in agreement with earlier publications in both visceral (Borysova et al .…”

“…; Hashitani et al . ). They exhibit a cytoskeleton similar to vascular SMCs and contain a number of proteins associated with the contractile phenotype including actin microfilaments, tropomyosin, cGMP‐dependent protein kinase and α‐smooth muscle actin (α‐SMA).…”

“…In this issue Hashitani et al . () report that mouse bladder suburothelial capillary pericytes are not influenced by perivascular nerves, based on electrical field stimulation experiments. Instead, the pericytes may respond to the metabolic state of capillary‐fed tissues (e.g.…”

Lamina propria: The connective tissue of rat urinary bladder mucosa

“…The vascular network of the bladder is vast and complex, and the ionic properties of, especially as regards calcium signaling, have been studied . Rather intriguing is the vascular network embedded on the basal aspect of the urothelium, demonstrated earlier on by scanning electron microscopy .…”