title: Activation of Ca2+-dependent currents in dorsal root ganglion neurons by metabotropic glutamate receptors and cyclic ADP-ribose precursors.
abstract: Cultured dorsal root ganglion neurons were voltage clamped at -90 mV to study the effects of intracellular application of nicotinamide adenine dinucleotide (betaNAD+), intracellular flash photolysis of caged 3',5'-cyclic guanosine monophosphate (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 betaNAD+. Whole cell Ca2+-activated inward currents were used as a physiological index of raised intracellular Ca2+ levels. Extracellular application of 10 microM glutamate evoked the activation of Ca2+-dependent inward currents, thus reflecting a rise in intracellular Ca2+ levels. Similar inward currents were also activated after isolation of metabotropic glutamate receptor activation by application of 10 microM glutamate in the presence of 20 microM 6-cyano-7-nitroquinoxaline-2,3-dione and 20 microM dizocilpine maleate (MK 801), or by extracellular application of 10 microM trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic acid. Intracellular photorelease of cGMP, from its caged axial isomer, in the presence of betaNAD+ was also able to evoke similar Ca2+-dependent inward currents. Intracellular application of betaNAD+ 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 bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid, and depletion of intracellular Ca2+ stores, but were insensitive to the removal of extracellular Ca2+. Therefore both cGMP, possibly via a mechanism that involves betaNAD+ and/or cyclic ADP-ribose, and glutamate can mobilize intracellular Ca2+ from ryanodine-sensitive stores in sensory neurons.
authors.affiliation: Merck Sharp and Dohme, Neuroscience Research Centre, Harlow, Essex, United Kingdom.
authors.forename: J H
authors.initials: JH
authors.lastname: Crawford
authors.forename: J F
authors.initials: JF
authors.lastname: Wootton
authors.forename: G R
authors.initials: GR
authors.lastname: Seabrook
authors.forename: R H
authors.initials: RH
authors.lastname: Scott
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000031:analogs & derivatives* / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D036563:Cyclic ADP-Ribose; D006152:Cyclic GMP / Q000502:physiology; D005727:Ganglia, Spinal / Q000166:cytology*; D018698:Glutamic Acid / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D009124:Muscle Proteins / Q000502:physiology; D009243:NAD / Q000502:physiology; D009474:Neurons / Q000166:cytology; D018408:Patch-Clamp Techniques; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000502:physiology*; D019837:Ryanodine Receptor Calcium Release Channel; D009435:Synaptic Transmission / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D009124:Muscle Proteins; D018094:Receptors, Metabotropic Glutamate; D019837:Ryanodine Receptor Calcium Release Channel; D009243:NAD; D036563:Cyclic ADP-Ribose; D000246:Adenosine Diphosphate Ribose; D018698:Glutamic Acid; D006152:Cyclic GMP; D002118:Calcium