Pharmacological characterization of native α7 nicotinic ACh receptors and their contribution to depolarization-elicited exocytosis in human chromaffin cells.

BACKGROUND AND
PURPOSE: Expression of α7 nicotinic acetylcholine receptors (nAChRs) and their role in exocytosis have not yet been examined in human chromaffin cells. EXPERIMENTAL APPROACH: To characterize these receptors and investigate their function, patch-clamp experiments were performed in human chromaffin cells from organ donors. KEY
RESULTS: The nicotinic current provoked by 300µM ACh in voltage-clamped cells was blocked by the nicotinic receptor antagonists α-bungarotoxin (α-Bgtx; 1µM; 6 ± 1.7%) or methyllycaconitine (MLA; 10nM; 7 ± 1.6%), respectively, in an irreversible and reversible manner, without affecting exocytosis. Choline (10mM) pulses induced a biphasic current with an initial quickly activated (5.5 ± 0.4ms rise time) and inactivated component (8.5 ± 0.4ms time constant) (termed α7), which was blocked by α-Bgtx or MLA, followed by a slower component (non-α7). α7 nAChR currents were dissected by blocking the non-α7 nAChR current component of the ACh and choline response with the α6* nAChR blocker α-conotoxin (α-Ctx) MII[S4A, E11A, L15A]. PNU-282987, an α7 nAChR-specific agonist, elicited rapidly activated and rapidly inactivated currents. α7 nAChR-positive allosteric modulators, such as 5-hydroxyindole (1mM) and PNU-120596 (10µM), potentiated responses that were blocked by α-Bgtx or MLA. Exocytosis was evoked by depolarization-elicited α7 nAChR currents, using choline in the presence of α-Ctx MII[MS4A, E11A, L15A] or PNU-282987 as agonists. CONCLUSIONS AND IMPLICATIONS: Our electrophysiological recordings of pure α7 nAChR currents elicited by rapid application of agonists demonstrated that functional α7 nAChRs are expressed and contribute to depolarization-elicited exocytosis in human chromaffin cells.