Oxygen sensing in the rabbit ductus arteriosus occurs via inhibition of a K_DR channel

The ductus arteriosus (DA) is a vital fetal structure which closes at birth, primarily in response to an increase in oxygen (O1) tension. The mechanism of the O₂-induced constriction of the DA remains uncertain. In the pulmonary artery, hypoxic vasoconstriction occurs via inhibition of a K⁺ channel. We therefore tested the hypothesis that O₂ causes DA constriction by inhibiting K⁺ channels. In isolated DA rings from late-geslation fetal rabbits, increasing O₂ levels from 20 to 130 Torr caused rapid and reversible constriction. Rings also constricted to low dose 4-aminopyridine (4-AP, 1-lOmM; n=13; selective for the delayed rectifier (KDR) K⁺ channel) but not to the Ca²⁺-dependent K⁺ channel blocker tetraethylammonium (1-IOmM; n=9) or the ATP-dependent K⁺ channel blocker, glibenclamide (1μM; n=13). Amphotericin-perforated patch-clamp studies, using freshly dispersed DA smooth muscle cells, showed that whole-cell, 4-AP-sensitive K⁺ channel currents were reversibly inhibited by increasing O₂ from 20 to 130 Torr. In current-clamp, cells were depolarized by increasing O₂ levels or by exposing the cell to lmM4-AP. These data suggest that O₂-induced DA constriction may be initialed by the inhibition of a 4-AP-sensitive K⁺ channel of the KDR type.