Structure-activity relationship of glibenclamide analogs: a comparison of potency as levcromakalim antagonists in rat aorta vs. affinity for [3H]-glibenclamide binding to membranes from rat cerebral cortex.

Glibenclamide and analogs were tested for their ability to antagonize the vasorelaxant actions of the K+ channel opener levcromakalim in rat thoracic aorta, and to displace [3H]-glibenclamide binding from rat cerebral cortex membranes. Aortic ring segments were suspended in organ baths to record isometric tension. Tissues were precontracted with K+ (20 mM), and full concentration-relaxation curves were constructed to levcromakalim (0.01-30 microM) in the absence and presence of glibenclamide or analog. The majority of the amidoethylbenzenesulfonylurea based compounds (exemplified by glibenclamide) caused parallel rightward shifts in the levcromakalim concentration-effect curves without effecting the maximum response to levcromakalim. Sulfonamide based compounds were generally inactive, with the exception of the compound DK#1 (laboratory code), which was unusually active as an antagonist of levcromakalim-mediated responses. The compounds were 1,000 to 10,000 times more potent at displacing [3H]-glibenclamide binding from rat cerebral cortex membranes. There was a strong correlation between the activity of amidoethylbenzenesulfonylurea based compounds as antagonists of the effects of levcromakalim and their ability to displace [3H]-glibenclamide binding. The slope of the regression line indicated that structural modification to these compounds has a more dramatic effect on their actions as levcromakalim antagonists than on their ability to displace [3H]-glibenclamide binding. This relationship of activity for the amidoethylbenzenesulfonylureas did not hold in the case of the sulfonamide derivatives. The results show that, for the processes characterized in this study (vascular levcromakalim antagonism vs. sulfonylurea receptor affinity), there are quantitative differences in their sensitivities to sulfonamide/sulfonylurea based compounds. Such differentiation may be important in the development of tissue-specific compounds.