INTERACTION OF GUANIDINIUM COMPOUNDS AND K-SITES IN RABBIT KIDNEY( CHANNEL MODULATORS WITH IMIDAZOLINE BINDING)

Several guanidinium compounds were tested for their ability to inhibit the binding of [H-3]idazoxan to the I-2 subtype of the imidazoline si te on rabbit kidney basolateral membranes. Phenformin, a biguanide, wa s the most potent with an IC50 of 50 +/- 3 mu M. Various K+ channel mo dulators were also evaluated for inhibition of [H-3]idazoxan binding. 1,2,3,4-Tetrahydro-9-aminoacridine and 4-aminopyridine (IC50 values of 38 +/- 5 mu M and 43 +/- 3 mu M, respectively) were the most effectiv e of the K+ channel blockers tested. Pinacidil, an ATP-sensitive K+ ch annel opener, inhibited radioligand binding with an IC50 of 100 +/- 10 mu M. The results indicate that I-2 sites are selective in their inte raction with guanidinium derivatives and K+ channel modulators.