Abstract

Peptides related to the N-terminal region of calcitonin gene-related peptide (CGRP) were tested for their ability to modulate neuronal nicotinic acetylcholine receptors (nAChRs) of rat cultured chromaffin cells under whole cell patch-clamp conditions. Although CGRP_1–7 and CGRP_2–7 depressed responses mediated by nAChRs, CGRP_1–6, CGRP_1–5, or CGRP_1–4 rapidly and reversibly potentiated submaximal nicotine currents while sparing maximal currents. CGRP_1–3was inactive. The threshold concentration for the enhancing effect of CGRP_1–6 was 0.1 μM. CGRP_1–5 or CGRP_1–4 were less effective than CGRP_1–6. Coapplication of CGRP_1–6 and of the allosteric potentiator physostigmine (0.5 μM) gave additive effects on nicotine currents. CGRP_1–6 did not enhance responses generated by muscle-type nicotinic receptors of cultured myoblasts or by γ-aminobutyric acid_A receptors expressed by human embryonic kidney cells. Molecular dynamics (MD) simulations suggested that CGRP_1–7exhibited a relatively rigid ring structure imparted by the disulfide bridge between Cys₂ and Cys₇. The circular dichroism (CD) spectrum recorded from the same peptide was in agreement with this result. Shorter peptides, missing such a bridge, exhibited propensity for α-helix configuration. Replacing Cys₇ with Ala yielded CGRP_1–7A, a fragment with partial α-helix structure and ability to enhance nicotine currents. CD measurements on CGRP_1–6 were compatible with these MD structural findings. Short terminal fragments of CGRP represent a novel class of substances with selective, rapid, and reversible potentiation of nAChRs.