Isosmotic Contraction of Rat Aortic Smooth Muscle Cells upon Activation of Purinergic Receptors: the Role of Chlorine Transport

We studied the effect of the purinergic signaling system andthe contribution of Cl^– transportersto isosmotic contraction of vascular smooth muscle cells (SMC),which results from the normalization of osmotic pressure after prolongedincubation in a hyposmotic medium. The study was carried out by myographyof endothelium-denuded aortic ring segments of male Wistar rats.Isosmotic contraction was induced by placing vascular segments innormosmotic Krebs solution (120 mM NaCl) after a 40-minute incubationin a hyposmotic Krebs solution (40 mM NaCl). Purinergic receptorswere activated by adenosine 5’-triphosphate (ATP, 500 µM), a nonselectiveP₂X and P₂Y receptoragonist, and uridine 5’-triphosphate (UTP, 500 µM), a selectiveP₂Y receptor agonist. ATP and UTP abolishedthe transience of the aortic SMC isosmotic contraction without affectingits amplitude. Pretreatment of vascular segments with ATP and UTPduring incubation in a hyposmotic solution completely suppressedthe development of isosmotic contraction in the presence of ATPor UTP, but did not affect it without purinergic receptor activators.The Na⁺–K⁺–2Cl^–-cotransporter(NKCC) inhibitor bumetanide (100 µM) abolished isosmotic contractionin the presence of ATP (not UTP) but restored its transience. Thenonselective Cl^– channel and Cl^–/HCO₃ ^– exchangerblocker DIDS (100 µM) suppressed the development of isosmotic contractionin the presence of both ATP and UTP. The potassium channel blocker tetraethylammonium(10 mM) potentiated the contractile activity of UTP toward isosmoticvolume contraction. Presumably, purinergic receptors abolish thetransience of isosmotic contraction by activating Cl^– currentsthrough activation of P₂Y receptors. Themechanism of interaction between the purinergic signaling systemand Cl^– transport during cell volumechanges requires further investigation.