K ATP channels predominantly regulate conduit vessel tone in normoxic cat pulmonary arteries in vivo

Abstract

Through our investigations of the intact pulmonary circulation, we aimed to find out whether K ATP channels contribute to regulating basal vascular tone and to clarify which vascular segments dilate during K ATP channel activation under basal tone conditions. Using an X-ray television system on anesthetized cat lungs, we measured internal diameter (ID) responses to two K ATP channel inhibitors (glibenclamide and 4-morpholinecarboximidine- N-1-adamantyl- N′-cyclohexyl-hydrochloride (U-37883A)) and to an activator (levcromakalim) in normoxic pulmonary arteries. In conduit arteries (800–3000 μm ID), the inhibitors and activator induced larger ID constrictions (14–17%) and dilatations (29–32%), respectively. However, in resistance arteries (<500 μm), the constriction response was negligible and the dilatation response relatively small (5–10%). The data suggest that K ATP channels are active and capable of regulating basal vascular tone primarily within conduit pulmonary arteries even though these channels are present in all pulmonary arteries.