Acute hypoxia is thought to cause vasoconstriction in pulmonary arteries, but relaxation in systemic arteries. It has been proposed that inhibition of 4-AP sensitive (delayed rectifier) K+ channels in pulmonary ASMCs mediate hypoxic pulmonary vasoconstriction. We tested this hypothesis by examining (1) whether there was a correlation between the hypoxia and 4-AP induced responses in porcine pulmonary and femoral ASMCs and (2) whether the hypoxic responses was altered by inhibiting delayed rectifier K+ channels. ASMCs were isolated enzymatically from proximal (> 1 cm o.d.) and distal (0.3-0.8 mm o.d.) intralobar pulmonary arteries and femoral arteries. [Ca2+], and cell-length of single freshly isolated ASMC were monitored simultaneously using Indo-1 AM and video-microscopy. A decrease in pO2 from 110 mmHg to < 10 mmHg had no effect in femoral and poximal pulmonary ASMCs. but caused small but significant increases in [Ca2+] and decreases in cell-length in distal PASMCs. In contrast, 4-AP (10 mM) increased [Ca2+]i and decreased cell-length in distal pulmonary and femoral ASMCs, but had no significant effect in proximal pulmonary ASMCs. All three types of myocytes responded to KCl (100 mM) to a similar extent. In the presence of 10 mM 4-AP, hypoxia elevated [Ca2+]i and caused cell-shortening in 3 of 7 distal PASMCs. The correlation of hypoxia and 4-AP induced responses in distal and proximal pulmonary PASMCs, and the inhibition of hypoxic responses in some distal pulmonary PASMCs by 4-AP is consistent with the hypothesis. However, the presence of responses to 4-AP, but not hypoxia in femoral ASMCs. and the presence of hypoxic responses in some 4-AP treated distal pulmonary ASMCs, suggest that additional mechanisms may be involved in responses of porcine pulmonary ASMCs to hypoxia.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology