Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC110
Reduced P2X receptor-mediated responses in renal vascular myocytes of spontaneously hypertensive rats.
O. Povstyan1,2, M. Harhun1, D. Gordienko1,2
1. Division of Biomedical Sciences, St George's University of London, London, United Kingdom. 2. Laboratory of Molecular Pharmacology and Biophysics of Cell Signalling, O.O.Bogomoletz Institute of Physiology, Kyiv, Ukraine.
P2X receptors (P2XRs) mediate sympathetic control and autoregulation of the renal circulation triggering contraction of renal vascular smooth muscle cells (RVSMCs) by elevation of [Ca2+]i . We have recently demonstrated that elevation of [Ca2+]i following activation of ionotropic P2XRs in RVSMCs is caused by Ca2+ entry through P2XRs and voltage-gated Ca2+ channels (VGCCs) and Ca2+-induced Ca2+ release from the sarcoplasmic reticulum (SR) mediated not only by ryanodine receptors (RyRs), but also by inositol 1,4,5-trisphosphate receptors (IP3Rs) . The aim of this work was to compare responses induced by stimulation of P2XRs with 10 μM of αβ-meATP in RVSMCs freshly isolated from spontaneously hypertensive rats (SHR) and their normotensive control, the Wistar Kyoto (WKY) rats. RVSMCs were isolated from arcuate and interlobular arteries of rat kidney, as previously described . P2XR-mediated cationic current (IP2X) was recorded using amphotericin B perforated patch-clamp method. Changes of [Ca2+]i in fluo-3 loaded RVSMCs were visualised using fast (33-40 Hz) x-y confocal imaging. Data are presented as mean ± S.E.M. The data groups were compared using unpaired Student’s t-test. We found significant (p<0.01) reduction of IP2X in RVSMCs from SHR: the peak current density was on average 57±7 pA/pF (n=18) in RVSMCs from SHR and 101±12 pA/pF (n=25) in RVSMCs from WKY. The peak amplitude of the αβ-meATP-induced [Ca2+]i transients was also significantly (p<0.001) reduced in SHR RVSMCs: mean ΔF/F0 was 1.6±0.1 (n=89) in RVSMCs from SHR and 3.9±0.2 (n=95) in RVSMCs from WKY. Relative contribution of Ca2+ entry through P2XRs to the αβ-meATP-induced elevation of [Ca2+]i was decreased in RVSMCs from SHR, while contribution of Ca2+ entry via VGCCs was increased. In spite of decreased SR Ca2+ load (tested with 10 mM caffeine) in RVSMCs of SHR, relative contribution of the SR Ca2+ release to the αβ-meATP-induced [Ca2+]i mobilisation was similar in both groups. Nevertheless, 100 mM ryanodine reduced the αβ-meATP-induced [Ca2+]i transients significantly stronger in SHR RVSMCs, while the effect of 30 mM 2-APB was similar in both groups. Our results suggest that in SHR: (1) both Ca2+ entry and Ca2+ release following P2X receptor activation in RVSMCs were significantly reduced and (2) the main cause of the Ca2+ release reduction was decrease of the SR Ca2+ load resulting from an enhanced RyR-mediated Ca2+ leak. Reduction of P2XR-mediated signals may underlie impairment of sympathetically driven and autoregulatory responses in renal vasculature leading to glomerular damage in hypertension.
Where applicable, experiments conform with Society ethical requirements