Two pharmacologically distinct components of nicotinic receptor-mediated rubidium efflux in mouse brain require the beta2 subunit.
Nicotinic agonist-stimulated efflux of 86Rb+ from mouse brain synaptosomes was monitored continuously by on-line radioactivity detection. The concentration-effect curve following a 5-s stimulation with acetylcholine was biphasic (EC50 = 7.2 and 550 microM). alpha-Bungarotoxin (100 nM) did not inhibit the response, but dihydro-beta-erythroidine (DHbetaE) blocked both phases with differing potency (average IC50 =.22 and 8.9 microM for responses activated by low and high acetylcholine concentrations, respectively). Differential sensitivity DHbetaE inhibition was used to measure stimulation of 86Rb+ efflux by 17 nicotinic agonists, which differed markedly in potency and efficacy. All agonists were more potent at the DHbetaE-sensitive site. Both components were inhibited by the six antagonists tested. Methyllycaconitine and DHbetaE were more potent for the DHbetaE-sensitive component, whereas hexamethonium was more potent at the DHbetaE-resistant component. Both DHbetaE-sensitive and DHbetaE-resistant responses were reduced more than 95% in beta2-null mutant mice, establishing the requirement for the beta2 subunit for both components. Both components were widely, but not identically, distributed throughout the brain. The DHbetaE-sensitive component appears to be identical with agonist-stimulated 86Rb+ efflux described previously and is likely to be mediated by alpha4beta2 receptors. The DHbetaE-resistant component is a novel, active, and widely distributed response mediated by nicotinic receptor(s) that also require the beta2 subunit.
Marks
M J
MJ
Institute for Behavioral Genetics, University of Colorado, Boulder, Colorado, USA.
Whiteaker
P
P
Calcaterra
J
J
Stitzel
J A
JA
Bullock
A E
AE
Grady
S R
SR
Picciotto
M R
MR
Changeux
J P
JP
Collins
A C
AC
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000648:ultrastructure; D002038:Bungarotoxins / Q000494:pharmacology; D004079:Dihydro-beta-Erythroidine / Q000494:pharmacology; D066298:In Vitro Techniques; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation / Q000502:physiology; D018722:Nicotinic Agonists / Q000494:pharmacology*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000235:genetics; D012413:Rubidium / Q000378:metabolism*; D012414:Rubidium Radioisotopes; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D002038:Bungarotoxins; D008024:Ligands; D018722:Nicotinic Agonists; D018733:Nicotinic Antagonists; D011978:Receptors, Nicotinic; D012414:Rubidium Radioisotopes; D004079:Dihydro-beta-Erythroidine; D012413:Rubidium; D000109:Acetylcholine