Restoring Nitric Oxide Cytosolic Calcium Regulation by Cyclic Guanosine Monophosphate Protein Kinase I Alpha Transfection in Coronary Endothelial Cells of Spontaneously Hypertensive Rats

In microcoronary endothelial cells (RCEs) from spontaneously hypertensive rats (SHR), the nitric oxide (NO)/cyclic guanosine monophosphate (GMP)-dependent proteinkinase I (cGKI) pathway cannot regulate the cytosolic calcium ([Ca²⁺]i) dynamic as in RCEs from Wistar Kyoto rats (WKY). We investigated the altered downstream NO target in SHR cells and, since cGKI expression was low, whether the re-expression of cGKIα in SHR RCEs could restore NO calcium responsiveness. We measured [Ca²⁺]i dynamic by fura-2 imaging analysis and the cGKI level by RT-PCR and Western blot in SHR and WKY RCEs. Plasmids encoding for enhanced green fluorescence protein or cGKIα-enhanced green fluorescence protein were transiently transfected in SHR RCEs, and [Ca²⁺]i was evaluated. Angiotensin-II (AT-II) increased [Ca²⁺]i in a concentration-dependent way in both strains. Whereas in WKY, endogenously produced NO and cyclic GMP analog decreased the AT-II-induced [Ca²⁺]i transient, they were ineffective in SHR RCEs. The cGKI level was low in SHR cells. However, after cGKIα re-expression, endogenous NO decreased the AT-II-induced [Ca²⁺]i transient, while endothelial NO synthase and cGKI inhibition prevented it. The low expression of cGKI in SHR accounts for the absent regulation of the agonist-induced [Ca²⁺]i transient by the NO/cyclic GMP pathway. Studies on cGKI in humans could contribute to a better understanding of cardiovascular pathologies.