Abnormal Ca2+ signalling in vascular endothelial cells from spontaneously hypertensive rats: role of free radicals

Objective To test the hypothesis that the Ca2+ signal transduction process in endothelial cells from genetically hypertensive rats (SHR) is affected b y an overproduction of free radicals. Methods The Ca2+ response to the inositol 1,4,5-triphosphate (IP3) mobilizi ng agonist, ATP, was measured using the fluorescent probe, fura-2, in endot helial cells from Sprague-Dawley rats, and in young and age-matched genetic ally hypertensive rats (SHR), The effect of free radicals and reducing agen ts on the intracellular release of Ca2+ and IP(3)production was determined in resting and ATP-stimulated cells. Experiments were also performed to com pare the level of expression and enzymatic activity of catalase and superox ide dismutase (SOD) in endothelial cells from SHR and Sprague-Dawley rats. Results The exposure of aortic endothelial cells from Sprague-Dawley rats t o the free-radical generating system, hypoxanthine + xanthine oxidase (HX/X O), caused a time- and concentration-dependent inhibition of the ATP-induce d Ca2+ response. A similar HX/XO-dependent inhibition was also observed in Sprague-Dawley cells stimulated with the endoplasmic reticulum Ca2+-ATPase inhibitor, thapsigargin, Incubation with the antioxidative enzymes, catalas e and SOD, had no effect on the ATP-induced Ca2+ release in Sprague-Dawley cells, but led to a strong increase in the internal release of Ca2+ in cell s from adult (12 weeks old) or young (3 weeks old) SHE, The effect of antio xidants was not related either to an enhancement of the ATP-induced product ion of IP3, or to a lower expression and activity of SOD and catalase, Conclusion The present work provides evidence that the Ca2+ signalling proc ess in SHR endothelial cells is affected by an overproduction of free radic als, resulting in a depletion of releasable Ca2+ from IP3-sensitive and ins ensitive Ca2+ pools. These results point towards a beneficial action of ant ioxidants on Ca2+ signalling in endothelial cells from models of hypertensi on. (C) 2001 Lippincott Williams & Wilkins.