A Novel Class of Peptides with Facilitating Action on Neuronal Nicotinic Receptors of Rat Chromaffin Cells in Vitro: Functional and Molecular Dynamics Studies

Abstract

Peptides related to the N-terminal region of calcitonin generelated 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 1-3 was inactive. The threshold concentration for the enhancing effect of CGRP 1-6 was 0.1 M. 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 M) gave additive effects on nicotine currents. CGRP 1-6 did not enhance responses generated by muscletype nicotinic receptors of cultured myoblasts or by ␥-aminobutyric acid A receptors expressed by human embryonic kidney cells. Molecular dynamics (MD) simulations suggested that CGRP 1-7 exhibited a relatively rigid ring structure imparted by the disulfide bridge between Cys 2 and Cys 7 . 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 ␣-helix configuration. Replacing Cys 7 with Ala yielded CGRP 1-7A , a fragment with partial ␣-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.

Apolipoprotein E-Derived Peptides Block α7 Neuronal Nicotinic Acetylcholine Receptors Expressed inXenopusOocytes

“…Similar to the data presented here, ␤-amyloid 1-42 has been shown to block ␣4␤2 receptors in a noncompetitive manner and at higher concentrations to block ␣7 receptors (Wu et al, 2004). Calcitonin gene-related peptide fragments have been shown to either inhibit or facilitate non-␣7-containing nAChR responses, depending on the peptide (Di Angelantonio et al, 2002). Recently, a peptide derived from the C-terminal region of AChE was demonstrated to modulate ␣7 but not ␣4␤2 nAChRs expressed in oocytes.…”

Positive and negative modulation of nicotinic receptors

“…Although other PAMs exist, the current information does not permit to separate them into type I or type II modulators yet. For instance, 17b-estradiol (Paradiso et al, 2001;reviewed in Arias and Bouzat, 2006), the ACh metabolite choline (Zwart and Vijverberg, 2000), and peptides derived from the C-terminus of acetylcholinesterase Zbarsky et al, 2004) and from the N-terminal region of calcitonin gene related peptide (CGRP) (i.e., CGRP1-6, CGRP1-5, and CGRP1-4) (Di Angelantonio et al, 2002.…”

Prefrontal neuromodulation by nicotinic receptors for cognitive processes

“…These growth factors and neuregulin-1 modulate nAChRs activity indirectly by binding to their own receptors. However, several peptides, like dynorphin A and calcitonin gene-related peptide, also affect nAChRs functions by direct interaction (Belluardo et al 2000;Itoh et al 2000;Di Angelantonio et al 2002). In addition, α4β2* and α7* nicotinic receptors colocalize with Lynx-1 in the somatodendritic compartment of neurons in several brain areas, such as the frontal cortex (cortical pyramidal neurons), amygdala, and hippocampus (Ibañez-Tallon et al 2002).…”