Figure 3.
Effect of CGRP1–6 and shorter CGRP fragments on nicotine-evoked currents. (a) Submaximal currents induced by a short nicotine pulse (20 ms) are potentiated by 1 μM CGRP1–6 fragment. (b) Dose–Response curve (expressed as pulse duration versus response) for nicotine in control and in the presence of CGRP1–6 (1 μM); the plot in the presence of the peptide is shifted to the left in a parallel manner without altering maximal responses (n=5–12). Currents are normalized with respect to response to 20 ms pulse in control solution and fitted with the logistic equation. P refers to significant difference between control and CGRP1–6 data indicated by asterisks. (c) Histograms summarizing the action of different fragments of CGRP (all compounds applied at 1 μM concentration) on nicotine-mediated responses. The efficacy of CGRP1–5 is less than the one observed with 1–6 fragments. CGRP1–4 maintains a slight potentiating effect, whereas CGRP1–3 is inactive. For comparison, data corresponding to the antagonism exerted by CGRP and CGRP1–7 are reported. Responses are expressed as ratios of currents (ICGRP) in the presence of CGRP or its fragment with respect to controls. P-values refer to significant differences with respect to control responses. Data are based on results by Di Angelantonio et al. (2002).