Metabotropic glutamate receptor activation and intracellular cyclic ADP-ribose release Ca2+ from the same store in cultured DRG neurones

The whole cell patch clamp technique has been used to record Ca2+-activated cation and chloride conductances evoked by release of Ca2+ from intracellular stores of cultured neonatal dorsal root ganglion neurones. The aim of this study was to investigate metabotropic glutamate receptor (mGluR) mechanisms and evaluate a possible role for cyclic ADP-ribose as an intracellular signalling molecule. Glutamate and the metabotropic glutamate receptor agonist (1S,3R)-ACPD-evoked transient depolarizations, Ca2+-activated inward currents and rises in intracellular Ca2+. The (1S,3R)-ACPD-activated currents were insensitive to InsP(3) signalling inhibitors, heparin and pentosan polysulphate. Intracellular application of ryanodine alone activated currents in this study and proved a difficult tool to use as a potential inhibitor of cyclic ADP-ribose-mediated responses. However, intracellular dantrolene did attenuate both (1S,3R)-ACPD and cyclic ADP-ribose responses. Intracellular photorelease of cGMP and cyclic ADP-ribose mimicked the responses to mGluR receptor activation. Intracellular application of nicotinamide and W7 inhibited the responses to photoreleased cGMP but did not prevent responses to mGluR activation. The cyclic ADP-ribose receptor antagonist 8-amino cyclic ADP-ribose attenuated responses to (1S,3R)-ACPD, cGMP and cyclic ADP-ribose, but some Ca2+-activated inward currents were still observed in the presence of this antagonist. In conclusion, mGluR receptor activation, cGMP and cyclic ADP-ribose release Ca2+ from intracellular stores. Some evidence suggests that pharmacologically related pathways are involved. (C) Harcourt Publishers Ltd 1999.