Potassium channels regulate tone in rat pulmonary veins

Intrapulmonary veins (PVs) contribute to pulmonary vascular resistance, but the mechanisms controlling PV tone are poorly understood. Although smooth muscle cell (SMC) K⁺ channels regulate tone in most vascular beds, their role in PV tone is unknown. We show that voltage-gated (K_v) and inward rectifier (K_ir) K⁺ channels control resting PV tone in the rat. PVs have a coaxial structure, with layers of cardiomyocytes (CMs) arrayed externally around a subendothelial layer of typical SMCs, thus forming spinchterlike structures. PVCMs have both an inward current, inhibited by low-dose Ba²⁺, and an outward current, inhibited by 4-aminopyridine. In contrast, PVSMCs lack inward currents, and their outward current is inhibited by tetraethylammonimn (5 mM) and 4-aminopyridine. Several K_v, K_ir, and large-conductance Ca²⁺-sensitive K⁺ channels are present in PVs. Immunohistochemistry showed that K_ir channels are present in PVCMs and PV endothelial cells but not in PVSMCs. We conclude that K⁺ channels are present and functionally important in rat PVs. PVCMs form sphincters rich in K_ir channels, which may modulate venous return both physiologically and in disease states including pulmonary edema.