Differential coupling of G‐protein‐linked receptors to Ca²⁺ mobilization through inositol(1,4,5)trisphosphate or ryanodine receptors in cerebellar granule cells in primary culture

Abstract

Rat cerebellar granule cells in primary culture possess muscarinic, metabotropic glutamatergic, histaminergic and alpha-adrenergic receptors which couple to phosphoinositide-specific phospholipase C. We have determined the ability of these receptors to elevate inositol(1,4,5)trisphosphate and to release intracellular calcium, in order to establish the correlation between these two responses. In resting cerebellar granule cells, only the muscarinic agonist carbachol evoked significant increases in both inositol(1,4, 5)trisphosphate and cytoplasmic free Ca2+. Mild depolarization (20 mM KCl) enhanced inositol(1,4,5)trisphosphate elevation by carbachol and histamine, but not by noradrenaline or the metabotropic glutamate agonist 1S,3R ACPD. In contrast, Ca2+-release responses were modified differently by 20 mM KCl-depolarization: the responses to carbachol, histamine and 1S,3R ACPD, but not the responses to noradrenaline, were markedly enhanced. The contribution of ryanodine-sensitive Ca2+-release channels (ryanodine receptors) to the calcium release signal in depolarized cells was determined. Ryanodine (10 microM) inhibited most effectively the cytoplasmic Ca2+ elevation evoked by 1S,3R ACPD (> 90%), while Ca2+ release upon stimulation by carbachol and histamine was only inhibited by approximately 60% and remained larger than in the absence of KCl. Our data are consistent with a specific coupling between metabotropic glutamate receptors and ryanodine-sensitive Ca2+-release channels which may not require generation of inositol(1, 4,5)trisphosphate.

Intracellular Calcium Regulation by Burst Discharge Determines Bidirectional Long-Term Synaptic Plasticity at the Cerebellum Input Stage

“…Local Ca 2ϩ control by synaptic stimuli is commonly observed in spines and smooth dendrites of pyramidal neurons (Svoboda et al, 1996;Sabatini et al, 2001Sabatini et al, , 2002Augustine et al, 2003;Goldberg et al, 2003). Ca 2ϩ signals observed in the soma of GrCs in culture (Irving et al, 1992a,b;del Rio et al, 1999;Masgrau et al, 2001) may reflect different recording or cellular conditions, as well as the massive, protracted nonlocalized stimulation caused by bath perfusion of high-K ϩ solutions or glutamate receptor agonists.…”

“…Glutamate released by mf discharge activated NMDA-Rs and mGlu-Rs (D' Angelo et al, 1993Angelo et al, , 1995Rossi et al, 1996). NMDA-Rs are permeable to Ca 2ϩ , and mGlu-Rs probably act through the IP 3 pathway, which is effectively stimulated by glutamate in GrCs (del Rio et al, 1999;Masgrau et al, 2001;Monti et al, 2002). During repetitive synaptic transmission, the main contribution to [Ca 2ϩ ] i was given by NMDA-R, whereas mGlu-R1 could play an amplifying role (Finch et al, 1991;Irving et al, 1992b), explaining the need for NMDA-R and mGlu-R coactivation in mf-GrC LTP induction (Rossi et al, 1996;D'Angelo et al, 1999;Maffei et al, 2002).…”

“…Moreover, although previous observations suggested the involvement of Ca 2ϩ -dependent mechanisms, these have never been investigated. Reports in cell culture have revealed Ca 2ϩ entering through NMDA and VDCCs and released by inositol 1,4,5-trisphosphate (IP 3 ) and ryanodinsensitive intracellular Ca 2ϩ stores (Irving et al, 1992a,b;Simpson et al, 1996;del Rio et al, 1999;Masgrau et al, 2001;Monti et al, 2002); however, because [Ca 2ϩ ] i changes were stimulated by exogenous drug application and measured in the soma, neither their input specificity nor their relationship with input patterns or synaptic plasticity could be assessed.…”

Recurrent Dendrodendritic Inhibition of Accessory Olfactory Bulb Mitral Cells Requires Activation of Group I Metabotropic Glutamate Receptors

“…These changes include spatially localized increases in intracellular calcium via activation of ryanodine receptors (Chavis et al, 1996;Finch and Augustine, 1998;Takechi et al, 1998;del et al, 1999), up or downregulation of potassium and calcium conductances (Charpak et al, 1990;Schoppa and Westbrook, 1997;Chavis et al, 1998;Fagni et al, 2000;Heinbockel et al, 2006), and reduction in the strength of electrical synapses (Landisman and Connors, 2005). These cellular responses often serve to regulate network "tone" and modulate the propagation and extent of neural activity.…”

“…In a number of cell types, activation of mGluRs is coupled to release of calcium from internal stores either via second messengers or calcium influx through voltage-gated calcium channels (VGCCs) (Chavis et al, 1996;Finch and Augustine, 1998;Takechi et al, 1998;del Rio et al, 1999). The experiments above indicate that calcium influx through VGCCs is necessary to evoke recurrent IPSCs but does not address the question of whether GABA release also depends on release of calcium from internal stores.…”