Cell type-specific differences in chloride-regulatory mechanisms and GABA(A) receptor-mediated inhibition in rat substantia nigra.
The regulation of intracellular chloride has important roles in neuronal function, especially by setting the magnitude and direction of the Cl- flux gated by GABA(A) receptors. Previous studies have shown that GABA(A)-mediated inhibition is less effective in dopaminergic than in GABAergic neurons in substantia nigra. We studied whether this phenomenon may be related to a difference in Cl-regulatory mechanisms. Light-microscopic immunocytochemistry revealed that the potassium-chloride cotransporter 2 (KCC2) was localized only in the dendrites of nondopaminergic (primarily GABAergic) neurons in the substantia nigra, whereas the voltage-sensitive chloride channel 2 (ClC-2) was observed only in the dopaminergic neurons of the pars compacta. Electron-microscopic immunogold labeling confirmed that KCC2 is localized in the dendritic plasma membrane of GABAergic neurons close to inhibitory synapses. Confocal microscopy showed that ClC-2 was selectively expressed in the somatic and dendritic cell membranes of the dopaminergic neurons. Gramicidin-perforated-patch recordings revealed that the GABA(A) IPSP reversal potential was significantly less negative and had a much smaller hyperpolarizing driving force in dopaminergic than in GABAergic neurons. The GABA(A) reversal potential was significantly less negative in bicarbonate-free buffer in dopaminergic but not in GABAergic neurons. The present study suggests that KCC2 is responsible for maintaining the low intracellular Cl- concentration in nigral GABAergic neurons, whereas a sodium-dependent anion (Cl--HCO3-) exchanger and ClC-2 are likely to serve this role in dopaminergic neurons. The relatively low efficacy of GABAA-mediated inhibition in nigral dopaminergic neurons compared with nigral GABAergic neurons may be related to their lack of KCC2.
Gulácsi
Alexandra
A
Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, H-1083 Hungary.
Lee
Christian R
CR
Sík
Attila
A
Viitanen
Tero
T
Kaila
Kai
K
Tepper
James M
JM
Freund
Tamás F
TF
D000818:Animals; D000090007:CLC-2 Chloride Channels; D002462:Cell Membrane / Q000378:metabolism; D018118:Chloride Channels / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003712:Dendrites / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D004558:Electric Stimulation; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000378:metabolism*; D013378:Substantia Nigra / Q000166:cytology / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism; D000096922:K Cl- Cotransporters
D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; D002712:Chlorides; D004298:Dopamine; D011963:Receptors, GABA-A; D027981:Symporters; D005680:gamma-Aminobutyric Acid; D000096922:K Cl- Cotransporters; C000715429:Clcn2 protein, rat