Hypoxia sensitivity of a voltage-gated potassium current in porcine intrapulmonary vein smooth muscle cells

Abstract

Hypoxia contracts the pulmonary vein, but the underlying cellular effectors remain unclear. Utilizing contractile studies and whole cell patch-clamp electrophysiology, we report for the first time a hypoxia-sensitive K ⁺ current in porcine pulmonary vein smooth muscle cells (PVSMC). Hypoxia induced a transient contractile response that was 56 ± 7% of the control response (80 mM KCl). This contraction required extracellular Ca ²⁺ and was sensitive to Ca ²⁺ channel blockade. Blockade of K ⁺ channels by tetraethylammonium chloride (TEA) or 4-aminopyridine (4-AP) reversibly inhibited the hypoxia-mediated contraction. Single-isolated PVSMC (typically 159.1 ± 2.3 μm long) had mean resting membrane potentials (RMP) of −36 ± 4 mV with a mean membrane capacitance of 108 ± 3.5 pF. Whole cell patch-clamp recordings identified a rapidly activating, partially inactivating K ⁺ current ( I _KH) that was hypoxia, TEA, and 4-AP sensitive. I _KH was insensitive to Penitrem A or glyburide in PVSMC and had a time to peak of 14.4 ± 3.3 ms and recovered in 67 ms following inactivation at +80 mV. Peak window current was −32 mV, suggesting that I _KH may contribute to PVSMC RMP. The molecular identity of the potassium channel is not clear. However, RT-PCR, using porcine pulmonary artery and vein samples, identified Kv _1.5, Kv _2.1, and BK, with all three being more abundant in the PV. Both artery and vein expressed STREX, a highly conserved and hypoxia-sensitive BK channel variant. Taken together, our data support the hypothesis that hypoxic inhibition of I _KH would contribute to hypoxic-induced contraction in PVSMC.