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 to ne and to clarify which vascular segments dilate during K-ATP channel activ ation under basal tone conditions. Using an X-ray television system on anes thetized cat lungs, we measured internal diameter (ID) responses to two K,, , channel inhibitors (glibenclamide and 4-morpholinecarboximidine-N-1-adama ntyl-N ' -cyclohexyl-hydrochloride (U-37883A)) and to an activator (levcrom akalim) in normoxic pulmonary arteries. In conduit arteries (800-3000 mum T D), the inhibitors and activator induced larger ID constrictions (14-17%) a nd dilatations (29-32%), respectively. However, in resistance arteries (< 5 00 mum), the constriction response was negligible and the dilatation respon se relatively small (5-10%). The data suggest that K-ATP channels are activ e and capable of regulating basal vascular tone primarily within conduit pu lmonary arteries even though these channels are present in all pulmonary ar teries. (C) 2001 Elsevier Science B,V. All rights reserved.