Calcium channels coupled to depolarization-evoked glutamate release in the myenteric plexus of guinea-pig ileum.
Glutamate is the major excitatory neurotransmitter in the CNS. The recent characterization of glutamate as a neurotransmitter in the enteric nervous system opened a new line of investigation concerning the role of glutamate in that system. The present study aimed to further characterize the enteric glutamate release and the calcium channels coupled to it. For this study the myenteric plexus-longitudinal muscle of guinea-pig ileum was stimulated with potassium chloride or with electrical pulses. The released glutamate was detected by spectrofluorimetry. Laser scanning confocal microscopy was used for analysis of immunolabeled enteric tissue for co-localization studies of calcium channels (N- and P/Q-type) and glutamate transporters (EAAC1). Here we report the effects of known Ca(2+)-channel blockers on glutamate release evoked by KCl-depolarization or electrical stimulation in the myenteric plexus. We find that N-type Ca(2+) channels control a major portion of evoked glutamate release from this system, with a very small contribution from L-type Ca(2+) channels. Moreover, alpha(1A)-like (P-type Ca(2+) channel) and alpha(1B)-like (N-type Ca(2+ )channel) immunoreactivity co-localized with glutamate transporters in the myenteric plexus. In addition, KCl-evoked or electrically stimulated glutamate release was sensitive to omega-agatoxin IVA, in a frequency-dependent manner, suggesting that P-type channels are also coupled to the release of glutamate. We, thus, conclude that both N-type and P-type Ca(2+) channels control most of the evoked glutamate release from the enteric nervous system, as also occurs in some parts of the CNS.
Reis
H J
HJ
Laboratório de Neurofarmacologia, Divisão de Biologia Celular, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Belo Horizonte 31270-901, MG, Brazil.
Massensini
A R
AR
Prado
M A
MA
Gomez
R S
RS
Gomez
M V
MV
Romano-Silva
M A
MA
D027322:Amino Acid Transport System X-AG; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects* / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism; D020865:Calcium Channels, P-Type / Q000187:drug effects / Q000378:metabolism; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D004558:Electric Stimulation; D005456:Fluorescent Dyes / Q000494:pharmacology; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects / Q000294:innervation* / Q000378:metabolism; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects* / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D009197:Myenteric Plexus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D026941:Sodium Channel Blockers; D015222:Sodium Channels / Q000378:metabolism; D027981:Symporters; D013779:Tetrodotoxin / Q000494:pharmacology
D027322:Amino Acid Transport System X-AG; D000906:Antibodies; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D050491:Glutamate Plasma Membrane Transport Proteins; D007211:Indoles; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D027981:Symporters; D018698:Glutamic Acid; D013779:Tetrodotoxin; C007293:DAPI; D011189:Potassium Chloride