Role of ATP and Cl<sup>–</sup> transporters in regulation of contractile activity of pulmonary artery smooth muscles in hyposmotic conditions

Abstract

Objective . The role of Cl – -transport in ATP-dependent regulation of contractile activity of rat pulmonary artery (PA) smooth muscle cells was studied. Design and methods . The study was performed on endotheliumdenuded ring segments of the PA of male Wistar rats. Mechanical tension was measured using organ bath technique. Contractions of the PA segments were induced by high-potassium solution (30 mM KCl), hyposmotic solution (40 mM NaCl), as well as restoration of the medium osmolarity (120 mM NaCl) after incubation in hyposmotic solution. Inhibitor of Na + , K + , 2Cl – cotransport (NKCC) bumetanide (10 μM, 30 minutes preincubation), nonselective Cl – -channel blocker SITS (100 μM) and Ca2 + -activated Cl – channels blocker niflumic acid (NA, 10 μM) were used to modulate the Cl – -transport. Results . ATP (10–500 μM) did not affect vascular tone of PA segments incubated in Krebs solution (120 mM NaCl), while 500 and 1000 μM ATP led to the development of transient contractions, the amplitude of which decreased in the presence of bumetanide, SITS and NA. Incubation of PA segments in a hyposmotic medium (40 mM NaCl) caused the development of transient contraction. Subsequent recovery of the medium osmolarity (120 mM NaCl) induced another transient contraction — isosmotic striction. ATP (500 μM) eliminated the relaxation phase of hyposmotic striction, and completely suppressed the development of isosmotic striction. Bumetanide did not affect the action of ATP during isosmotic striction, but restored the relaxation phase of hyposmotic striction. SITS and NA eliminated the effect of ATP on hypo- and isosmotic striction. Conclusions . The constrictive effect of ATP on the smooth muscle cells of the PA is associated with the activation of mechanisms of transmembrane Cl – -redistribution, in which NKCC and Ca2 + -activated Cl – channels are involved.