Run-down of the GABAA response under experimental ischaemia in acutely dissociated CA1 pyramidal neurones of the rat.
1. The effect of experimental ischaemia on the response to gamma-aminobutyric acid (GABA) was assessed in acutely dissociated CA1 pyramidal neurones of rats, using the patch-clamp technique. 2. Rapid application of 3 x 10(-5) M GABA induced a bicuculline-sensitive inward Cl- current (IGABA) at a holding potential (Vh) of -44 mV. The peak amplitude of IGABA showed a time-dependent decrease (run-down) when it was recorded with the conventional whole-cell mode without internal ATP. The run-down was not observed when the intracellular ATP concentration ([ATP]i) was maintained by the nystatin-perforated recording with an intracellular Na+ concentration ([Na+]i) of 0 mM. 3. When [Na+]i was increased to more than 30 mM, the IGABA run-down was observed even with the nystatin-perforated recording. 4. The IGABA run-down observed at 60 mM [Na+]i with the nystatin method was further enhanced under experimental ischaemia without changes in the reversal potential of IGABA. The enhanced run-down was suppressed by application of the Na+,K(+)-ATPase inhibitors, ouabain and SPAI-1. 5. IGABA run-down during ischaemia was also accompanied by an outward holding current and a concomitant increase in intracellular free Ca2+ concentration ([Ca2+]i) in 48.5% of the neurones. The outward current was a Ca(2+)-activated K+ current, which was blocked by 3 x 10(-7) M charybdotoxin. 6. In the inside-out mode of the single-channel analysis, GABA activated three subconductance states with conductances of 33.4, 22.7 and 15.2 pS. Reduction of ATP concentration from 2 to 0 mM on the intracellular side suppressed the channel activities, while an increase in Ca2+ concentration from 0.7 x 10(-9) to 1.1 x 10(-6) M had no effect. 7. These results suggest that ischaemia induces the run-down of the postsynaptic GABA response at the GABAA receptor level, and that this run-down is triggered by a decrease in [ATP]i.
Harata
N
N
Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Wu
J
J
Ishibashi
H
H
Ono
K
K
Akaike
N
N
D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002545:Brain Ischemia / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism; D004594:Electrophysiology; D066298:In Vitro Techniques; D007476:Ionophores; D008564:Membrane Potentials / Q000502:physiology; D009761:Nystatin; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D011963:Receptors, GABA-A / Q000502:physiology*; D015290:Second Messenger Systems / Q000502:physiology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D018118:Chloride Channels; D007476:Ionophores; D011963:Receptors, GABA-A; D009761:Nystatin; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium