The effect of depolarizing potassium concentrations on the efflux of GABA from rat dorsal medulla in vivo and from slices and synaptosomes.
The efflux of [3H]GABA from the dorsal surface of adult rat medulla overlying the dorsal column nuclei (DCN) was found not be influenced by increasing the concentration of potassium in the superfusing solution to 40 mequiv. Similarly, raised potassium was found not to influence the efflux from slices of the dorsal region of the caudal medulla containing the dorsal column nuclei. This lack of effect of raised potassium is not thought to be due to lack of GABAergic terminals in this region because there is good pharmacological evidence for their presence and bacause both electrical stimulation and 100 microM veratridine increased the efflux of [3H]GABA from such slices. Also, 40 mequiv potassium was found to increase the efflux of both endogenous and [3H]GABA from crude synaptosome preparations of this region without influencing the efflux of [14C]sucrose or [3H]leucine. This release of [3H]GABA was calcium-dependent, and was similar whether produced by 20, 40 of 60 mequiv potassium and occurred whether eos or AOAA was used to inhibit GABA metabolism. Release from synaptosomes could also be induced with 100 microM veratridine. Raised potassium was additionally found to prevent the increased efflux from slices produced by electrical stimulation and to increase the efflux from slices prepared from the brains of rats 14 days old. It is suggested that the astrocytic swelling produced by raised potassium concentration restricts the diffusion of GABA away from depolarized terminals.
D000625:Aminooxyacetic Acid / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000625:Aminooxyacetic Acid; D005680:gamma-Aminobutyric Acid; D011188:Potassium; D002118:Calcium