INHIBITION BY HISTAMINE H-1 RECEPTOR ANTAGONISTS OF ENDOGENOUS GLIBENCLAMIDE-SENSITIVE K-ENCLOSED XENOPUS-OOCYTES( CHANNELS IN FOLLICLE)

Effects of histamine receptor ligands on the glibenclamide-sensitive K + currents induced by K+ channel openers, cromakalim and Y-26763, were examined in follicle-enclosed Xenapus oocytes. Histamine H-1 receptor antagonists, promethazine, dimethindene and chlorpheniramine all decr eased cromakalim-induced K+ currents with IC50 values of 31.5 mu M, 29 .5 mu M and 138 mu M, respectively. These compounds also blocked Y-267 63-induced K+ currents with comparable IC50 values. Histamine (1 mM) a nd histamine H-2 receptor antagonists, cimetidine (0.5 mM) and ranitid ine (1 mM) had little effect on these K+ currents. These results sugge st that histamine H-1 receptor antagonists inhibit glibenclamide-sensi tive K+ currents by a mechanism other than the histamine H-1 receptor antagonism. The inhibitory effects might explain, in part, the reporte d actions of histamine H-1 receptor antagonists in ischemia.