The non-GABAergic nature of 3H-baclofen binding in rat peripheral tissues.
In peripheral tissues from organs such as the kidney, liver and spleen, specific binding of 3H-baclofen was most highly detected in the kidney, and that in the liver and spleen was approximately one-tenth that in the kidney. The amount of specific binding did not differ at a room temperature of 20-25 degrees C or 0-4 degrees C, and equilibration occurred within 10 min. Divalent cations (Ca2+, Mg2+, Mn2+ and Ni2+) and monovalent cations (Na+ and K+) did not increase the specific binding, yet in higher concentrations, they decreased both specific and non-specific binding. Specific binding showed a single component, Kd and Bmax of which were 6.35 microM and 79 pmol/mg protein, respectively. The binding was stereospecific; (-)baclofen was 150 times as potent as (+)baclofen. Some of the structural analogues of baclofen inhibited 3H-baclofen binding whereas GABA and its related compounds showed little or no inhibition. Bmax of the binding in the kidney of spontaneously hypertensive rats (SHR) was higher by 28% than that of normotensive Wistar-Kyoto rats (WKY), whereas the Kd values did not differ. These results indicate that specific 3H-baclofen binding in the rat peripheral tissues is entirely different from the binding in the central nervous system (GABAB sites).
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D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000378:metabolism*; D001667:Binding, Competitive; D002122:Calcium Chloride / Q000494:pharmacology; D002412:Cations; D007668:Kidney / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D018377:Neurotransmitter Agents / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D011919:Rats, Inbred Strains; D011921:Rats, Inbred WKY; D011963:Receptors, GABA-A / Q000378:metabolism; D013154:Spleen / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology / Q000502:physiology*
D002412:Cations; D018377:Neurotransmitter Agents; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; D002122:Calcium Chloride