Figure 2.
One-hour CGRP treatment upregulates P2X3 receptor-mediated responses in TG neurons. Sister culture dishes were used in parallel for control data and for experiments testing the consequences of a 1 h application of CGRP, washed out before studying neurons with Ca2+ imaging or patch clamping. A, Example of α,β-meATP (10 μm, 2 s; arrow) or KCl (50 mm, 1 s; open arrowheads) evoked Ca2+ transients in control condition. After 1 h CGRP (1 μm) treatment, the effect of α,β-meATP is comparatively larger, whereas the response to KCl is similar (different cell from control). B, Examples of currents evoked by α,β-meATP (10 μm, 2 s; open bars) in control or after a 1 h treatment with CGRP, in the presence or absence of the CGRP receptor antagonist CGRP8–37 (2 μm), which fully prevents the potentiation of current responses. C, CGRP significantly increases α,β-meATP-induced peak current (expressed as percentage of control; n = 78), an effect antagonized by CGRP8–37 (n = 11), which has no effect per se (n = 15). D, Dose–response curves for α,β-meATP in the control condition (○; n = 10) and after 1 h CGRP treatment (•; n = 12). The EC50 value is not altered by CGRP, whereas the peak current amplitude is increased. E, Concentration-dependent effect of CGRP on α,β-meATP-induced peak currents saturates near 1 μm. The dashed line indicates the mean value in the control condition (n = 16); n = 10–15 for CGRP treatments. F, G, CGRP accelerates P2X3 receptor recovery from desensitization evoked by α,β-meATP (open bar) tested in this example at a 30 s interval between pulses. CGRP treatment significantly decreases the half-time of recovery (measured as percentage of the first response amplitude and tested over an extended time interval; ○, n = 15 control; •, n = 11 CGRP). ∗p < 0.05; ∗∗p < 0.01; ∗∗∗p < 0.00001. α,β, α,β-meATP; 8-37, CGRP8–37.