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The Journal of Neuroscience, April 15, 1999, 19(8):2945-2953
Calcitonin Gene-Related Peptide Rapidly Downregulates Nicotinic
Receptor Function and Slowly Raises Intracellular Ca2+ in
Rat Chromaffin Cells In Vitro
R.
Giniatullin1, 3,
Silvia
Di Angelantonio1, 2,
Cristina
Marchetti1,
Elena
Sokolova1, 3,
L.
Khiroug1, 2, and
A.
Nistri1, 2
1 Biophysics Sector and 2 Istituto
Nazionale di Fisica della Materia Unit, International School for
Advanced Studies (SISSA), 34014 Trieste, Italy, and
3 Physiology Department, Kazan Medical University, 42000 Kazan, Russia
Although calcitonin gene-related peptide (CGRP) modulates
muscle-type nicotinic acetylcholine receptors (nAChRs) via
intracellular second messenger-mediated phosphorylation, the action of
this peptide on neuronal-type nAChRs remains unknown. Using neuronal nAChRs of rat chromaffin cells in vitro we studied the
effect of CGRP, which is physiologically present in adrenal medulla, on
membrane currents and [Ca2+]i
transients elicited by nicotine. Our main novel observation was that
CGRP (either bath-applied or focally applied for a few seconds or even
co-applied with nicotine for a few milliseconds) selectively and
rapidly blocked nAChRs (a phenomenon unlikely caused by intracellular
messengers in view of its speed) without affecting GABA
receptors. The inhibitory effect of CGRP was independent of
[Ca2+]i or membrane potential and not
accompanied by baseline current changes. Like the competitive
antagonist
N,N,N-trimethyl-1-(4-trans-stilbenoxy)-2-propilammonium, CGRP induced a rightward, parallel shift of the nicotine dose-response curve; during co-application of these blockers the nicotine dose-ratio value was the sum of the values obtained with each antagonist alone. The block by CGRP was insensitive to the receptor antagonist hCGRP8-37 but mimicked by CGRP1-7. Persistent
application of CGRP slowly increased
[Ca2+]i, a phenomenon
independent from external Ca2+, thus implying
Ca2+ release from internal stores, and suppressed by
hCGRP8-37. CGRP1-7 had no significant effect
on [Ca2+]i. We propose that the 1-7
amino acid sequence of CGRP was responsible for the direct, rapid block
of nAChRs, whereas the full-length peptide molecule was necessary for
the delayed rise in internal Ca2+ potentially able
to trigger phosphorylation-dependent modulation of nicotinic receptor function.
Key words:
CGRP; CGRP antagonist; neuropeptide; nicotine; calcium
imaging; intracellular calcium; receptor modulation
Copyright © 1999 Society for Neuroscience 0270-6474/99/1982945-09$05.00/0
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