Gap junctions support the sustained phase of hypoxic pulmonary vasoconstriction by facilitating calcium sensitization

Abstract

Aims To determine the role of gap junctions (GJs) in hypoxic pulmonary vasoconstriction (HPV). Methods and results Studieswere performed in rat isolated intrapulmonary arteries (IPAs) mounted on a myograph and in anaesthetized rats. Hypoxia induced a biphasic HPV response in IPAs preconstricted with prostaglandin F2α (PGF2α, 3 μM) or 20 mMK+. The GJ inhibitors 18β-glycyrrhetinic acid (18β-GA, 30 μM), heptanol (3.5 μM), or 2-aminoethoxydiphenyl borate (2-APB) (75 μM) had little effect on the transient Phase 1 of HPV, but abolished the sustained Phase 2 which is associated with Ca2+ sensitization. The voltage-dependent Ca2+ channel blocker diltiazem (10 μM) had no effect on HPV, and did not alter the inhibitory action of 18β-GA. Sustained HPV is enhanced by high glucose (15 μM) via potentiation of Ca2+ sensitization, in the presence of high glucose 18β-GA still abolished sustained HPV. Simultaneous measurement of tension and intracellular Ca2+ using Fura PE-3 demonstrated that whilst 18β-GA abolished tension development during sustained HPV, it did not affect the elevation of intracellular Ca2+. Consistent with this, 18β-GA abolished hypoxia-induced phosphorylation of the Rho kinase target MYPT-1. In anaesthetized rats hypoxia caused a biphasic increase in systolic right ventricular pressure. Treatment with oral 18β-GA (25 mg/kg) abolished the sustained component of the hypoxic pressor response. Conclusion These results imply that GJs are critically involved in the signalling pathways leading to Rho kinase-dependent Ca2+ sensitization during sustained HPV, but not elevation of intracellular Ca2+, and may explain the dependence of the former on an intact endothelium.