Pharmacological dissection of calcium channel subtype-related components of strontium inflow in large mossy fiber boutons of mouse hippocampus.
Several subtypes of voltage-dependent calcium channels (VDCCs) are present in the presynaptic terminals. In the mammalian hippocampus, P/Q-, N-, and R- but not L-type VDCCs are involved in the fast transmitter release from large mossy fiber (MF) boutons, which are associated with CA3 pyramidal cell dendrites. We investigated whether L-type VDCCs are indeed absent in these large MF boutons. With the use of Sr2+ as the Ca2+ substitute, the stimulus-evoked Sr2+ increment (delta[Sr2+]pre) was evaluated fluorometrically. Delta[Sr2+]pre appeared to be proportional to Sr2+ inflow through VDCCs and was specifically attenuated by conventional VDCC subtype-selective antagonists. The P/Q-type selective omega-agatoxin IVA (AgTx(IVA)) blocked delta[Sr2+]pre with an IC50 of 28 nM and by 30-35% at its maximum effective concentration of 0.5 microM. The N-type selective omega-conotoxin GVIA (CgTx(GVIA)) blocked delta[Sr2+]pre with an IC50 of 15 nM and by 20-25% at its maximum effective concentration of 1 microM. The R-type selective SNX-482 blocked delta[Sr2+]pre with an IC50 of 79 nM and by 20-25% at its maximum effective concentration of 1 microM. The effects of these toxins did not overlap at their maximum effective concentrations and about 70-80% of delta[Sr +]pre was blocked by the simultaneous exposure to these toxins. delta[Sr2+]pre component that is resistant to AgTx(IVA), CgTx(IVA), and SNX-482 was significantly potentiated by an L-type agonist, (S)-(-)-Bay K8644, and attenuated by an L-type antagonist, nimodipine, suggesting that L-type VDCCs are present in large MF terminals. The L-type agonist, (+/-)-Bay K8644, also potentiated Sr2+ inflow into individual boutons identified as large MF boutons under confocal microscopy. Almost similar results were observed for Ca2+ inflow-dependent fluorescence increments. L-type VDCCs appear to be present in large MF boutons and mediate a substantial Ca2+ inflow into presynaptic terminals during action potentials.
Department of Physiology and Pharmacology, Tohoku University Graduate School of Medicine, Sendai, Japan.
Takashi
T
Tokunaga
Kenichi
K
Miyazaki
Makoto
M
Koseki
Jalal Izadi
JI
Mobarakeh
Toru
T
Ishizuka
Hiromu
H
Yawo
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D051379:Mice; D008807:Mice, Inbred BALB C; D019599:Mossy Fibers, Hippocampal / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism*; D013111:Spider Venoms / Q000494:pharmacology; D013324:Strontium / Q000378:metabolism* / Q000494:pharmacology; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D020867:omega-Agatoxin IVA / Q000494:pharmacology; D020866:omega-Conotoxin GVIA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D005456:Fluorescent Dyes; C115521:SNX 482; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D020866:omega-Conotoxin GVIA; D013324:Strontium