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 ro le in PV tone is unknown. We show that voltage-gated (K-V) and inward recti fier (K-ir) K+ channels control resting PV tone in the rat. PVs have a coax ial structure, with layers of cardiomyocytes (CMs) arrayed externally aroun d a subendothelial layer of typical SMCs, thus forming spinchterlike struct ures. PVCMs have both an inward current, inhibited by low-dose Ba2+, and an outward current, inhibited by 4-aminopyridine. In contrast, PVSMCs lack in ward currents, and their outward current is inhibited by tetraethylammonium (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 PVSM Cs. We conclude that K+ channels are present and functionally important in rat PVs. PVCMs form sphincters rich in K-ir channels, which may modulate ve nous return both physiologically and in disease states including pulmonary edema.