Modulation of calcium movements by urocortin II in endothelial cells

Background: In endothelial cells urocortin II has recently been found to activate nitric oxide synthase through cAMP-dependent and Ca ²⁺ - related pathway. Aim: The present study was therefore planned to determine the mechanisms of urocortin II effect on Ca ²⁺ movements. Methods. In Fura-2 loaded porcine aortic endothelial cells (PAE), the effects of urocortin II on [Ca ²⁺ ]c were analyzed and compared with those of various K ⁺ channels agonists/antagonists. Results: In Fura-2 loaded PAE, urocortin II promoted a transient increase of [Ca ²⁺ ]c mainly originating from an intracellular pool sensitive to thapsigargin and slightly from the extracellular space. In addition, urocortin II caused the hyperpolarization of plasma membrane through the opening of K ⁺ channels, which contributed to the increased [Ca ²⁺ ]c. These effects were abolished by the corticotropin releasing factor receptors (CRFR2) blocker, the adenylyl cyclase and Ca ²⁺ -calmodulin-kinase (CaMKII) inhibitors and by blockers of K ⁺ channels. In addition, in PAE cultured in Na ⁺ -free medium or loaded with the plasma-membrane Ca ²⁺ pump inhibitor the urocortin II-evoked Ca ²⁺ transient was slower. Conclusion: The results obtained show that urocortin II affects intracellular Ca ²⁺ homeostasis in PAE by both promoting a discharge of intracellular pool and by interfering with the operation of store-dependent channels through CRFR2-cAMP-CaMKII related signalling and K ⁺ channels opening.