CHARACTERIZATION AND LOCALIZATION OF ADRENAL NICOTINIC ACETYLCHOLINE-RECEPTORS - EVIDENCE THAT MAB35-NICOTINIC RECEPTORS ARE THE PRINCIPAL RECEPTORS MEDIATING ADRENAL CATECHOLAMINE SECRETION

Adrenal chromaffin cells contain at least two subtypes of nicotinic ac etylcholine receptors (nAChRs), These studies were designed to identif y and characterize the subtype of nAChR mediating adrenal catecholamin e release using the monoclonal antibody mAb35, which recognizes the al pha-subunit of muscle nAChRs and crossreacts with some neuronal nAChRs . Immunocytochemical studies demonstrated that mAb35 interacts with sp ecific sites on cultured chromaffin cells, Pretreatment with mAb35 red uced nAChR-stimulated catecholamine release (IC50 of similar to 10 nM) , mAb35 had no effects on release stimulated through non-nAChR mechani sms. Unlike agonist-induced nAChR desensitization, the mAb35-induced r eduction in nAChR-mediated secretion developed slowly. Although not im mediately reversible, nAChR-stimulated release recovered after mAb35 r emoval. However, unlike recovery from agonist pretreatment, recovery f rom mAb35 pretreatment was relatively slow and was partially blocked b y vinblastine. Hybridization of adrenal chromaffin RNA with a rat alph a 3 cDNA revealed two strong bands and two fainter bands: two higher-m olecular-weight bands, 6.9 and 8.5 kb; a strong band of 3.2 kb, and a lower amount of a 2.3-kb RNA. With recovery of nAChR function after ag onist or mAb35 treatment, no significant effects on alpha 3 subunit mR NA levels were seen. In summary, these studies demonstrate the presenc e of mAb35-nAChRs on adrenal chromaffin cells and provide evidence tha t these receptors represent the major population that regulates secret ory events in adrenal chromaffin cells.