Depolarization-evoked GABA release from myenteric plexus is partially coupled to L-, N-, and P/Q-type calcium channels.
1. There are many evidences suggesting that gamma-aminobutyrate (GABA) is an important neurotransmitter and/or neuromodulator in the gut. 2. Using the myenteric plexus-longitudinal muscle preparation from the guinea pig ileum, we investigated the evoked release of [3H] GABA from enteric neurons by electrical pulses or high KCl, which occurs in a calcium-dependent and -independent way. In addition, using selective calcium channel blockers, we report the participation of distinct subtypes of calcium channels in the evoked release, showing a minor participation of L- and Q-type calcium channels, while N- and P-type have a participation of approximately 15%, each. However, regardless of the combination of Ca2+ channel blockers, we did not observe an inhibition greater than 50% of the calcium-dependent component of [3H] GABA release. 3. Thus, while the observed Ca2+-independent release mostly probable occur via reversal of the membrane GABA transporter, in our conditions, a considerable portion of the Ca2+-dependent evoked release of [3H] GABA is not coupled to L-, N-, or P/Q-type calcium channels, suggesting the involvement of intracellular calcium stores or other ways of getting calcium across the membrane.
Reis
Helton J
HJ
Laboratório de Neurofarmacologia, Departamento de Farmacologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
Bíscaro
Fabrício V
FV
Gomez
Marcus V
MV
Romano-Silva
Marco A
MA
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism; D020907:Calcium Channels, Q-Type / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000187:drug effects / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D004558:Electric Stimulation; D050485:GABA Plasma Membrane Transport Proteins; D006168:Guinea Pigs; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism; D026901:Membrane Transport Proteins; D009130:Muscle, Smooth / Q000294:innervation* / Q000502:physiology; D009197:Myenteric Plexus / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009924:Organ Culture Techniques; D027361:Organic Anion Transporters; D011189:Potassium Chloride / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D020907:Calcium Channels, Q-Type; D002352:Carrier Proteins; D050485:GABA Plasma Membrane Transport Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D027361:Organic Anion Transporters; D005680:gamma-Aminobutyric Acid; D011189:Potassium Chloride