Effects of nitric oxide on P2Y receptor resensitization in spontaneously hypertensive rat mesangial cells

Cellular responses to agonists of G protein-coupled receptors are usually rapidly attenuated - a process known as 'receptor desensitization'. The mechanisms that attenuate signalling are important both physiologically and therapeutically.

To evaluate the effects of nitric oxide on the P2Y receptor resensitization in cultured glomerular mesangial cells in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats.

The cytosolic calcium concentration ([Ca2+]i ) in cultured mesangial cells was determined with a fluorescence digital imaging system, using the intracellular fluorescent indicator, Fura 2-AM.

The first ATP-stimulated [Ca2+]i measured was significantly greater in SHRs (1330.25 +/- 360.31 nmol/l) than in WKY rats (974.28 +/- 397.72 nmol/l; 0.05). Spermine- -[4-[1-(3-aminopropyl)-2-hydroxy-2-nitrosohydrazino]-butyl-1,3-propanediamine (spermine NONOate) and L-arginine significantly increased the fourth ATP-stimulated [Ca2+]i in WKY rats ( P<0.01, 0.05, respectively). In SHRs, only spermine-NONOate was able to restore the fourth ATP-challenged [Ca2+]i value significantly. Nomega-nitro-L-arginine methyl ester (L-NAME) greatly reduced the second, third and fourth ATP-stimulated [Ca2+]i in WKY rats (P< 0.01), but not in SHRs. When the cells from WKY rats were superfused with L-NAME, L-arginine or spermine-NONOate for a period of 5 min before and during one single ATP challenge, the responses observed were not significantly different from those in controls.

L-Arginine and spermine-NONOate are able to increase P2Y receptor resensitization in rat mesangial cells, an effect that is less potent in SHRs than in WKY rats. The presence of >l-NAME enhanced receptor desensitization in WKY rats, but not in SHRs.