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RGS2 regulates urotensin II‐induced intracellular Ca2+ elevation and contraction in glomerular mesangial cells

Urotensin II (UII), a kidney‐localized vasoactive peptide regulates renal functions, including renal blood flow, glomerular filtration rate, urine output, and electrolyte excretion. In the present study, the physiological functions of UII and regulation of UII receptor (UTR) in glomerular mesangial cells (GMCs) were investigated. RT‐PCR, Western immunoblotting, and immunofluorescence indicated the expression of UTR in murine GMCs. Mouse UII (mUII) elevated intracellular Ca2+ concentration ([Ca2+]i) and decreased murine GMC surface area by ~ 55 and 20%, respectively. mUII‐induced [Ca2+]i elevation and contraction in the cells were attenuated by SB 657510, a UTR antagonist, araguspongin B, an inositol 1,4,5‐trisphosphate receptor inhibitor, thapsigargin, a sarco/endoplasmic reticulum Ca2+‐ATPase inhibitor, and La3+, a store‐operated Ca2+ channel blocker. mUII‐induced [Ca2+]i elevation in murine GMCs was reduced by ~ 82% in Ca2+‐free medium. However, nimodipine, an L‐type Ca2+channel blocker did not alter mUII‐induced [Ca2+]i elevation and contraction in the cells. Co‐immunoprecipitation, co‐localization, and in situ ligation proximity assay demonstrated that UTR interacts with regulator of G‐protein signaling (RGS) 2 in murine GMCs. Biotinylation indicated that RGS2 is predominantly localized intracellularly in murine GMCs. However, mUII treatment elevated RGS2 surface expression in the cells by ~ 55%. siRNA‐mediated knockdown of RGS2 in murine GMCs increased mUII‐induced [Ca2+]i elevation and contraction by ~ 35 and 31%, respectively. These findings indicate that mUII induces store‐operated Ca2+ entry and contraction in murine GMCs. These data also suggest that mUII stimulates recruitment of RGS2 protein to GMC plasma membrane as a negative feedback mechanism to regulate UTR activation.