mGluR1 agonists elicit a Ca2+ signal and membrane hyperpolarization mediated by apamin-sensitive potassium channels in immature rat Purkinje neurons

The type 1 metabotropic glutamate receptor (mGluR1) plays an import role in the synaptic physiology and development of cerebellar Purkinje neurons. mGluR1 expression occurs early in the developmental program of Purkinje neurons, at an age that precedes expression of the dendritic structure. Few studies have investigated the physiological response produced by mGluR1 activation in early-developing Purkinje neurons. To address this question, simultaneous recording of membrane potential and intracellular Ca2+ was performed in immature cultured Purkinje neurons coupled with exogenous application of mGluR1 agonists. Membrane potential was measured using the perforated patch method of whole-cell recording, and intracellular Ca2+ was measured using fura-2-based Ca2+ imaging. Brief, 1-sec micropressure application of the group I mGluR-selective agonist (S)-3,5-dihydroxyphenylglycine (DHPG) evoked a prominent Ca2+ signal and coincident fast hyperpolarization in the immature neurons. The mGluR1-selective antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester blocked the Ca2+ signal and fast hyperpolarization, confirming the involvement of mGluR1s. Amplitude of the fast hyperpolarization varied as a function of membrane potential and intracellular Ca2+ and was blocked by apamin, an antagonist of the small-conductance Ca2+-activated K+ channel (SK), identifying this K+ channel as an underlying mechanism. In similar experiments with mature cultured Purkinje neurons, DHPG elicited a Ca2+ signal, but fast membrane hyperpolarization was not evident. These results suggest that mGluR1 activation and the resulting release of Ca2+ from intracellular stores and activation of SK channels may be a mechanism through which mGluR1 can modulate neuronal excitability of Purkinje neurons during early development. (C) 2007 Wiley-Liss, Inc.