Modulation of spontaneous intracellular Ca2+ fluctuations and spontaneous cholinergic transmission in rat chromaffin cells in situ by endogenous GABA acting on GABA(A) receptors
Por:
Tzitzitlini, Alejandre-Garcia, Pedro, Segura-Chama, Martha, Perez-Armendariz E., Rodolfo, Delgado-Lezama, Arturo, Hernandez-Cruz
Publicada:
1 feb 2016
Resumen:
Using fluorescence [Ca2+](i) imaging in rat adrenal slices, we
characterized the effects of agonists and antagonists of the GABA(A)
receptor (GABA(A)-R) on resting intracellular Ca2+ ([Ca2+](i)) and
spontaneous [Ca2+](i) fluctuations (SCFs) in hundreds of individual
chromaffin cells (CCs) recorded simultaneously in situ. Muscimol, a
GABA(A)-R agonist (20 mu M; 25 s), induced an increase of resting
[Ca2+](i) in 43 +/- 3 % of CCs, a decrease in 26 +/- 2 %, and no
response in 30 +/- 5 %. In Ca2+-free external medium, SCFs ceased
completely and muscimol failed to elicit [Ca2+](i) rises. All
muscimol-induced [Ca2+](i) changes were blocked by the GABA(A)-R
antagonist bicuculline, suggesting that they result from changes in
membrane potential depending on the cell's Cl- equilibrium potential.
Unexpectedly, bicuculline increased the amplitude and frequency of SCFs
in 54 % of CCs, revealing a tonic inhibition of SCFs by ambient GABA
acting through GABA(A)-R. Mecamylamine (a specific nicotinic cholinergic
blocker) decreased basal SCF activity in 18 % of CCs and inhibited
bicuculline-induced SCF intensification, suggesting that spontaneous
acetylcholine (ACh) release from nerve endings contributes to SCF
generation in CCs in situ and that blockade of presynaptic GABA(A)-Rs
intensifies SCFs in part through the disinhibition of spontaneous
cholinergic transmission. Electrophysiological experiments confirmed
that spontaneous excitatory postsynaptic currents recorded from CCs in
situ were enhanced by bicuculline. To our knowledge, this is the first
description of a regulatory effect of endogenous GABA on synaptic
currents and SCFs of adrenal CCs. These findings denote a novel
GABA-mediated presynaptic and postsynaptic regulatory mechanism of CC
activity which may participate in the control of catecholamine
secretion.
Filiaciones:
Tzitzitlini, Alejandre-Garcia:
Univ Nacl Autonoma Mexico, Inst Fisiol Celular, Dept Neurociencia Cognit, Mexico City 04510, DF, Mexico
Pedro, Segura-Chama:
Univ Nacl Autonoma Mexico, Inst Fisiol Celular, Lab Nacl Canalopatias, Mexico City 04510, DF, Mexico
Unidad Invest Med Expt, Mexico City, DF, Mexico
Martha, Perez-Armendariz E.:
Univ Nacl Autonoma Mexico, Fac Med, Dept Biol Celular & Tisular, Mexico City 04510, DF, Mexico
Rodolfo, Delgado-Lezama:
IPN, Ctr Invest & Estudios Avanzados, Dept Fisiol Biofis & Neurociencias, Mexico City 07738, DF, Mexico
Arturo, Hernandez-Cruz:
Univ Nacl Autonoma Mexico, Inst Fisiol Celular, Dept Neurociencia Cognit, Mexico City 04510, DF, Mexico
Univ Nacl Autonoma Mexico, Inst Fisiol Celular, Lab Nacl Canalopatias, Mexico City 04510, DF, Mexico
|