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

Abstract

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 Ca(2+) 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 Ca(2+) was measured using fura-2-based Ca(2+) imaging. Brief, 1-sec micropressure application of the group I mGluR-selective agonist (S)-3,5-dihydroxyphenylglycine (DHPG) evoked a prominent Ca(2+) signal and coincident fast hyperpolarization in the immature neurons. The mGluR1-selective antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester blocked the Ca(2+) signal and fast hyperpolarization, confirming the involvement of mGluR1s. Amplitude of the fast hyperpolarization varied as a function of membrane potential and intracellular Ca(2+) and was blocked by apamin, an antagonist of the small-conductance Ca(2+)-activated K(+) channel (SK), identifying this K(+) channel as an underlying mechanism. In similar experiments with mature cultured Purkinje neurons, DHPG elicited a Ca(2+) signal, but fast membrane hyperpolarization was not evident. These results suggest that mGluR1 activation and the resulting release of Ca(2+) 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.

Control of neuronal excitability by Group I metabotropic glutamate receptors

“…In dopaminergic neurons of the ventral tegmental area and substantia nigra, synaptic glutamate acts through mGlu 1 receptors to release stored Ca 2+ that activates SK channels resulting in a slow glutamatergic IPSP (Fiorillo and Williams 1998). A similar result has been observed in primary culture of cerebellar Purkinje cells (Netzeband and Gruol 2008).…”

Third Trimester‐Equivalent Ethanol Exposure Does Not Alter Complex Spikes and Climbing Fiber Long‐Term Depression in Cerebellar Purkinje Neurons from Juvenile Rats

“…In support of this possibility, mGluR1 activation has been shown to induce SK channel-mediated membrane potential hyperpolarization in hippocampal and medial prefrontal cortical neurons (El-Hassar et al, 2011, Hagenston et al, 2008). Moreover, application of (S)-3,5-dihydroxyphenylglycine, a selective agonist of mGluR1, was shown to elicit Ca 2+ transients that coincided with SK channel-mediated fast membrane potential hyperpolarizations in immature cultured PCs (Netzeband and Gruol, 2008). Thus, it is possible that intracellular Ca 2+ evoked by CF-mediated activation of mGluR1 in PCs activates a pool of SK channels that mediate a portion of the CS AHP.…”

Ethanol Alters Opioid Regulation of Ca2+Influx Through L‐Type Ca2+Channels in PC12 Cells

“…Intracellular Ca 2+ levels were determined using standard microscopic fura-2 digital Ca 2+ imaging techniques (Grynkiewicz et al, 1985) as described previously (Netzeband and Gruol, 2008). At 2–5 days in vitro, PC12 cultures were incubated for 30 min with the membrane-permeable Ca 2+ -sensitive dye fura-2 AM (Molecular Probes-Invitrogen, Carlsbad, CA) at 3 μM in physiological saline containing 0.02 % pluronic F-127 (Molecular Probes) at room temperature in the dark.…”

“…Perforated-patch whole-cell current-clamp recordings were made from the PC12 cells using standard techniques as described previously (Netzeband and Gruol, 2008). The patch pipette solution contained: NaCl 6 mM, K + -methylsulfate 140 mM, MgCl 2 2 mM, CaCl 2 0.5 mM, HEPES-KOH 10 mM and glucose 10 mM.…”