Regulation of intracellular Cl- levels by Na(+)-dependent Cl- cotransport distinguishes depolarizing from hyperpolarizing GABAA receptor-mediated responses in spinal neurons

摘要: Rohon-Beard (RB) spinal neurons of Xenopus larvae are depolarized by GABA. To study the mechanisms underlying this distinctive response, intracellular and patch-clamp recordings were made from RB in situ. The intracellularly recorded GABA reversal potential (EREV) was near -30 mV normal saline approximately 25 more negative Na(+)-free saline. Whole-cell neighboring dorsolateral interneurons (DLi) revealed that responses both cells mediated GABAA receptors. Currents elicited mimicked muscimol reversibly blocked bicuculline, EREV shifted with changes Cl- concentration ([Cl]) agreement selectivity. In perforated patch recordings, for significantly positive than DLi (-38 vs -63 mV), indicating intact maintain higher levels Cl-. Replacement external Na+ or exposure to transport inhibitor bumetanide (100 microM) cell move values, consistent Na+(-)dependent Cl cotransport contributing internal [Cl]. contrast, these treatments did not change EREV. results indicate a mechanism underlies receptor-mediated depolarizing conductances neurons. Thus, inhibitory excitatory appear be present during same developmental period vivo. may stimulate Ca2+ influx because is above threshold low voltage-activated channels.