ACTIVATION OF CA2-DEPENDENT CURRENTS IN DORSAL-ROOT GANGLION NEURONS BY METABOTROPIC GLUTAMATE RECEPTORS AND CYCLIC ADP-RIBOSE PRECURSORS()

Cultured dorsal root ganglion neurons were voltage clamped at -90 mV t o study the effects of intracellular application of nicotinamide adeni ne dinucleotide (beta NAD(+)), intracellular flash photolysis of caged 3',5'-cyclic guanosine monophosphate (cGMP), and metabotropic glutama te receptor activation. The activation of metabotropic glutamate recep tors evoked inward Ca2+-dependent currents in most cells. This was mim icked both by intracellular flash photolysis of the caged axial isomer of cGMP [P-1-(2-nitrophenyl)ethyl cGMP] and intracellular application of beta NAD(+) Whole cell Ca2+-activated inward currents were used as a physiological index of raised intracellular Ca?+ levels. Extracellu lar application of 10 mu M glutamate evoked the activation of Ca2+-dep endent inward currents, thus reflecting a rise in intracellular Ca2+ l evels. Similar inward currents were also activated after isolation of metabotropic glutamate receptor activation by application of 10 mu M g lutamate in the presence of 20 mu M 6-cyano-7-nitroquinoxaline-2,3-dio ne and 20 mu M dizocilpine maleate (MK 801), or by extracellular appli cation of 10 mu M trans-(1S,3R)-1-amino-1,3-cyclopentanedicarboxylic a cid. Intracellular photorelease of cGMP, from its caged axial isomer, in the presence of beta NAD(+) was also able to evoke similar Ca2+-dep endent inward currents. Intracellular application of beta NAD(+) 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 intracellula r Ca2+ by bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid, and depleti on of intracellular Ca2+ stores, but were insensitive to the removal o f extracellular Ca2+. Therefore both cGMP, possibly via a mechanism th at involves beta NAD(+) and/or cyclic ADP-ribose, and glutamate can mo bilize intracellular Ca2+ from ryanodine-sensitive stores in sensory n eurons.