RESUMO
Ca(2+)-dependent mechanisms are important in regulating synaptic transmission. The results herein indicate that whole-cell perfusion of inositol 1,4,5-trisphosphate receptor (IP(3)R) agonists greatly enhanced excitatory postsynaptic current (EPSC) amplitudes in postsynaptic hippocampal CA1 neurons. IP(3)R agonist-mediated increases in synaptic transmission changed during development and paralleled age-dependent increases in hippocampal type-1 IP(3)Rs. IP(3)R agonist-mediated increases in EPSC amplitudes were inhibited by postsynaptic perfusion of inhibitors of Ca(2+)/calmodulin, PKC and Ca(2+)/calmodulin-dependent protein kinase II. Postsynaptic perfusion of inhibitors of smooth endoplasmic reticulum (SER) Ca(2+)-ATPases, which deplete intracellular Ca(2+) stores, also enhanced EPSC amplitudes. Postsynaptic perfusion of the IP(3)R agonist adenophostin (AdA) during subthreshold stimulation appeared to convert silent to active synapses; synaptic transmission at these active synapses was completely blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Postsynaptic IP(3)R-mediated Ca(2+) release also produced a significant increase in spontaneous EPSC frequency. These results indicate that Ca(2+) release from intracellular stores play a key role in regulating the function of postsynaptic AMPARs.
Assuntos
Adenosina/análogos & derivados , Canais de Cálcio/fisiologia , Cálcio/metabolismo , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Hipocampo/citologia , Inositol 1,4,5-Trifosfato/análogos & derivados , Neurônios/fisiologia , Receptores Citoplasmáticos e Nucleares/fisiologia , Transmissão Sináptica/fisiologia , 2-Amino-5-fosfonovalerato/farmacologia , 6-Ciano-7-nitroquinoxalina-2,3-diona/farmacologia , Adenosina/farmacologia , Fatores Etários , Animais , Animais Recém-Nascidos , Bicuculina/farmacologia , Western Blotting/métodos , Agonistas dos Canais de Cálcio/farmacologia , Interações Medicamentosas , Estimulação Elétrica/métodos , Inibidores Enzimáticos/farmacologia , Antagonistas de Aminoácidos Excitatórios/farmacologia , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Potenciais Pós-Sinápticos Excitadores/efeitos da radiação , Antagonistas GABAérgicos/farmacologia , Regulação da Expressão Gênica no Desenvolvimento/efeitos dos fármacos , Hipocampo/crescimento & desenvolvimento , Técnicas In Vitro , Indóis/farmacologia , Inositol 1,4,5-Trifosfato/farmacologia , Receptores de Inositol 1,4,5-Trifosfato , Neurônios/efeitos dos fármacos , Neurônios/efeitos da radiação , Técnicas de Patch-Clamp/métodos , Picrotoxina/farmacologia , Ratos , Receptores Citoplasmáticos e Nucleares/agonistas , Receptores Citoplasmáticos e Nucleares/antagonistas & inibidores , Transmissão Sináptica/efeitos dos fármacos , Tapsigargina/farmacologia , Fatores de TempoRESUMO
We show that activation of postsynaptic inositol 1,4,5-tris-phosphate receptors (IP(3)Rs) with the IP(3)R agonist adenophostin A (AdA) produces large increases in AMPA receptor (AMPAR) excitatory postsynaptic current (EPSC) amplitudes at hippocampal CA1 synapses. Co-perfusion of the Ca(2+) chelator bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid strongly inhibited AdA-enhanced increases in EPSC amplitudes. We examined the role of AMPAR insertion/anchoring in basal synaptic transmission. Perfusion of an inhibitor of synaptotagmin-soluble n-ethylmaleimide-sensitive factor attachment protein (SNAP) receptor SNARE-mediated exocytosis depressed basal EPSC amplitudes, whereas a peptide that inhibits GluR2/3 interactions with postsynaptic density-95 (PDZ) domain proteins glutamate receptor interacting protein (GRIP)/protein interacting with C-kinase-1 (PICK1) enhanced basal synaptic transmission. These results suggest that constitutive trafficking and anchoring of AMPARs help maintain basal synaptic transmission. The regulation of postsynaptic AMPAR trafficking involves synaptotagmin-SNARE-mediated vesicle exocytosis and interactions between AMPARs and the PDZ domains in GRIP/PICK1. We show that inhibitors of synaptotagmin-SNARE-mediated exocytosis, or interactions between AMPARs and GRIP/PICK1, attenuated AdA-enhanced increases in EPSC amplitudes. These results suggest that IP(3)R-mediated Ca(2+) release can enhance AMPAR EPSC amplitudes through mechanisms that involve AMPAR-PDZ interactions and/or synaptotagmin-SNARE-mediated receptor trafficking.
