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

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 microm ID), the inhibitors and activator induced larger ID constrictions (14-17%) and dilatations (29-32%), respectively. However, in resistance arteries (<500 microm), 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.