The Journal of Neuroscience, May 1, 2003, 23(9):3669
Evidence for Long-Lasting Cholinergic Control of Gap Junctional
Communication between Adrenal Chromaffin Cells
Agnès O.
Martin1, 2,
Marie-Noëlle
Mathieu1, and
Nathalie C.
Guérineau1
1 Institut National de la Santé et de la
Recherche Médicale (INSERM) Unité 469, Centre National de
la Recherche Scientifique/INSERM de Pharmacologie et d'Endocrinologie,
34094 Montpellier Cedex 5, France, and 2 Division of
Molecular Neurobiology, National Institute for Medical Research, London
NW7 1AA, United Kingdom
We investigated long-lasting interactions that may occur between
two forms of intercellular signaling: cholinergic synaptic transmission
and gap junction-mediated coupling in the rat adrenal medulla. The
junctional coupling between chromaffin cells was studied during reduced
or blocked synaptic transmission in adrenal slices. First, cholinergic
synaptic activity was reduced by pharmacological treatment.
Bath-application of the nicotinic receptor antagonists hexamethonium,
the oxystilbene derivative F3, or
-bungarotoxin, acting at distinct
neuronal-like postsynaptic nicotinic acetylcholine receptors (nAChRs),
significantly increased the incidence of Lucifer yellow passage
(dye coupling) between chromaffin cells (p > 0.7 in treated slices vs p = 0.4 in controls).
Dye coupling was associated with an elevated macroscopic conductance of
the junctional current measured by dual patch-clamp. Pharmacological
inhibition of protein trafficking from the trans-Golgi network to the
plasma membrane by either brefeldin A or nocodazole pretreatment
prevented the effects of nAChR antagonists on dye coupling.
Interestingly, this upregulation of gap junction-mediated coupling in
response to reduced synaptic activity is of physiological relevance,
because it is found in the newborn rat, in which cholinergic synaptic transmission has not yet matured. This mechanism may also be of importance in pathological conditions, because chronic blockade of
synaptic transmission after surgical denervation of the adrenal gland
also resulted in increased dye coupling between chromaffin cells. In
conclusion, our pharmacological, physiological, and pathological data
concur to demonstrate that gap junction-mediated intercellular
communication between chromaffin cells undergoes persistent adaptation
in response to impairment of synaptic activity. These results strongly
suggest that gap junctional communication between chromaffin cells is
under tonic inhibitory control exerted by cholinergic synaptic inputs.
Key words:
synaptic transmission; gap junctions; nicotinic
receptors; rat adrenal slices; splanchnectomized rats; dye coupling; neonates; hexamethonium; brefeldin A; nocodazole
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