Activation of Ca2+-dependent currents in cultured dorsal root ganglion
neurones from neonatal rats by metabotropic glutamate receptor activation and
intracellular áNAD+ and cGMP, the precursors to cyclic ADP-ribose formation.
Jane H. Crawford, John F. Wootton, Guy R. Seabrook, Roderick H. Scott.
Merck Sharp & Dohme, Neuroscience Research Centre, Terlings Park, Harlow,
Essex CM20 2QR, Fax 01279 440 390, E-mail jane_crawford@merck.com.
APStracts 4:0055N, 1997.
ABSTRACT
Cultured dorsal root ganglion (DRG) neurones were voltage clamped at -90 mV to
study the effects of intracellular application of áNAD+ , intracellular flash
photolysis of caged cGMP and metabotropic glutamate receptor activation. The
activation of metabotropic glutamate receptors evoked inward Ca2+-dependent
currents in most cells. This was mimicked both by intracellular flash
photolysis of the caged axial isomer of cGMP (P-1-(2-nitrophenyl)ethyl cGMP)
and intracellular application of áNAD+. Whole cell Ca2+ activated inward
currents were used as a physiological index of raised intracellular Ca2+
levels. Extracellular application of 10 ĉM glutamate evoked the activation of
Ca2+-dependent inward currents thus reflecting a rise in intracellular Ca2+
levels. Similar inward currents were also activated following isolation of
metabotropic glutamate receptor activation by application of 10 ĉM glutamate
in the presence of 20 ĉM CNQX and 20 ĉM MK 801, or by extracellular
application of 10 ĉM (1S,3R)-ACPD. Intracellular photorelease of cGMP, from
its caged axial isomer, in the presence of áNAD+ was also able to evoke
similar Ca2+-dependent inward currents. Intracellular application of áNAD+
alone produced a concentration-dependent effect on inward current activity.
Responses to both metabotropic glutamate receptor activation and cGMP were
suppressed by intracellular ryanodine, chelation of intracellular Ca2+ by
BAPTA, and depletion of intracellular Ca2+ stores, but were insensitive to the
removal of extracellular Ca2+. Therefore, both cGMP, possibly via a mechanism
that involves áNAD+ and/or cyclic ADP-ribose, and glutamate can mobilize
intracellular Ca2+ from ryanodine sensitive stores in sensory neurones.
Received 15 October 1996; accepted in final form 29 January 1997.
APS Manuscript Number J816-6
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 20 February 1997