Regulation of N- and L-type Ca2+-channels in Adult Frog Sympathetic
Ganglion B-cells by Nerve Growth Factor in vitro and in vivo.
SAOBO LEI, WILLIAM F. DRYDEN AND PETER A. SMITH.
Department of Pharmacology and Division of Neuroscience, University of
Alberta, Edmonton, Alberta, CANADA, T6G 2H7.
APStracts 4:201N, 1997.
ABSTRACT
To examine mechanisms responsible for the long-term regulation of Ca2+-
channels in an adult neuron, changes in whole-cell Ba2+ current (IBa) were
examined in adult bullfrog sympathetic ganglion B-cells in vitro. Cells were
cultured at low density in defined, serum-free medium. After 15d, total IBa
was similar to the initial value whereas IBa density was reduced by about 36%,
presumably due to an increase in neuronal surface area. By contrast, IBa
density remained constant after 6-15d in the presence of murine á-NGF
(200ng/ml) and total IBa was almost doubled. Inclusion of cytosine arabinoside
(Ara-C; 10 æM) to inhibit proliferation of non-neuronal cells, did not affect
the survival of neurons in the absence of NGF nor did it attenuate IBa. Ara-C
did not prevent the effect of NGF on IBa. There were three independent
components to the action of NGF; over 6-9 days, it increased -conotoxin-GVIA-
sensitive N-type IBa (IBa,N); increased nifedipine-sensitive L-type IBa
(IBa,L) and decreased inactivation of the total Ba2+ conductance (gBa). The
latter effect involved a selective decrease in the amplitude of one of the
four kinetic components that describe the inactivation process. Total IBa was
also 55.8% larger than control in the somata of B-cells acutely dissociated
from leopard frogs that had received prior subcutaneous injections of NGF. By
contrast, injection of NGF antiserum decreased total IBa by 29.4%. There was
less inactivation of gBa in B-cells from NGF-injected animals than in cells
from animals injected with NGF antiserum (P<0.001). These data suggest that
NGF-like molecule(s) play(s) a role in the maintenance of IBa in an adult
amphibian sympathetic neuron; the presence of NGF may allow the neuron to
maintain a constant relationship between cell size and current density. They
also show that IBa inactivation in an adult neuron can be modulated in a
physiologically-relevant way by an extracellular ligand.
Received 2 May 1997; accepted in final form 21 August 1997.
APS Manuscript Number J351-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997