Gamma-hydroxybutyrate receptor function determined by stimulation of rubidium and calcium movements from NCB-20 neurons.
Gamma-Hydroxybutyrate is derived from GABA in brain and plays specific functional roles in the CNS. It is thought to exert a tonic inhibitory control on dopamine and GABA release in certain brain areas, through specific gamma-hydroxybutyrate receptors. Apart from modifying certain calcium currents, the specific transduction mechanism induced by stimulation of gamma-hydroxybutyrate receptors remains largely unknown. We investigated the possible contribution of K(+) channels to the hyperpolarization phenomena generally induced by gamma-hydroxybutyrate in brain, by monitoring (86)Rb(+) movements in a neuronal cell line (NCB-20 cells), which expresses gamma-hydroxybutyrate receptors. Physiological concentrations of gamma-hydroxybutyrate (5-25 microM) induce a slow efflux of (86)Rb(+), which peaks at 5-15 min and returns to baseline levels 20 min later after constant stimulation. This effect can be reproduced by the gamma-hydroxybutyrate receptor agonist NCS-356 and blocked by the gamma-hydroxybutyrate receptor antagonist 6,7,8,9-tetrahydro-5-[H]-benzocycloheptene-5-ol-4-ylidene. The GABA(B) receptor antagonist CGP 55845 has no effect on gamma-hydroxybutyrate-induced (86)Rb(+) efflux. The pharmacology of this gamma-hydroxybutyrate-dependent efflux of (86)Rb(+) is in favor of the involvement of tetraethylammonium and charybdotoxin insensitive, apamin sensitive Ca(2+) activated K(+) channels, identifying them as small conductance calcium activated channels. We demonstrated a gamma-hydroxybutyrate dose-dependent entry of calcium ions into NCB-20 neuroblastoma cells at resting potential. Electrophysiological data showed that this Ca(2+) entry corresponded mainly to a left-hand shift of the current/voltage relation of the T-type calcium channel. This process must at least partially trigger small conductance calcium activated channel activation leading to gamma-hydroxybutyrate-induced hyperpolarization.
Kemmel
V
V
Institut de Chimie Biologique and INSERM U-338, Faculté de Médecine, 11 rue Humann, 67085, Strasbourg Cedex, France.
Taleb
O
O
Andriamampandry
C
C
Aunis
D
D
Maitre
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D011956:Receptors, Cell Surface / Q000819:agonists / Q000378:metabolism*; D012413:Rubidium / Q000378:metabolism*; D012978:Sodium Oxybate / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism
C039403:4-hydroxybutyric acid receptor; D011956:Receptors, Cell Surface; D012978:Sodium Oxybate; D012413:Rubidium; D002118:Calcium