No abstract

Currents from smooth muscle cells isolated from the pulmonary arterial tree of the rat were recorded under voltage clamp using the whole cell configuration of the patch-clamp technique. Rapid increases in cytosolic free calcium evoked by flash photolysis of Nitr-5 activated a current that, following ion substitution and pharmacological experiments, proved to be carried by Cl-. This current [ICl(Ca)] was evoked independently of photolytic by-products and, although smaller, was still activated in the absence of pipette ATP. Experiments revealed that ICl(Ca) was evoked in 80% in the cells isolated from the main pulmonary artery but only in 43% of the cells isolated from small vessels (200-400 microns ID). Application of caffeine also resulted in activation of ICl(ca), although the response current magnitude was larger in the main pulmonary artery. Photolysis of Nitr-5 still activated ICl(ca) in the presence of caffeine, suggesting that Ca2-release is not a prerequisite for activation of ICl(ca). These results represents in the first electrophysiological recordings of Cl- currents from small pulmonary arterial vessels and indicate that their Ca2+ regulation and/or distribution may be different throughout the pulmonary circulation.

SUMMARYUsing the patch-clamp recording technique, we observed that endothelin-1 (ET-1; 0.8-16nM) enhanced a voltage-activated outward current ('out) and induced periodic oscillations of inward current in smooth muscle cells isolated from small pulmonary arteries (200-400 ,um in diameter). Anion substitution experiments revealed that the ET-1-induced inward current was carried by Clions. Application of bosentan (10 #m; an ETA and ETB receptor antagonist) and FR 139317(1-10 uM; a selective ETA receptor antagonist) prevented initiation of inward currents or enhancement of Iout by ET-1. The ETB receptor agonist tetra-Ala-endothelin-1 (1 -20 nM) failed to evoke these responses. Caffeine (10 mM) induced a single transient inward current and prevented any further activation of inward current, or enhancement of Iout, by subsequent application of 16 nm ET-1, suggesting that these currents were mediated by Ca2' release from internal stores. Rapid intracellular release of Ca2' by photolysis of nitr-5 activated an inward Clcurrent and increased the magnitude of Iout These results demonstrate the existence of Ca2+_ activated Cl-and K+ channels in pulmonary arterial smooth muscle. The physiological role of these channels is at present uncertain, although their activation may be involved in the contractile responses of pulmonary arterial smooth muscle to ET-1.