{'fraction_non_alphanumeric': 0.02741514360313316, 'fraction_numerical': 0.006527415143603133, 'mean_word_length': 5.257142857142857, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Hyperpolarizing GABAergic Transmission Requires the KCC2 C-Terminal ISO Domain

KCC2 is the neuron-specific member of the of K+-Cl− cotransporter gene family. It is also the only member of its family that is active under physiologically normal conditions, in the absence of osmotic stress. By extruding Cl− from the neuron under isotonic conditions, this transporter maintains a low concentration of neuronal Cl−, which is essential for fast inhibitory synaptic transmission by GABA and glycine in the mature nervous system. The other members of this K+-Cl− cotransporter gene family are exclusively swelling-activated. Here we demonstrate that a 15 aa region near the end of the C terminus, unique to KCC2 (termed the ISO domain), is required for KCC2 to cotransport K+ and Cl− out of the neuron under isotonic conditions. We made this discovery by overexpressing chimeric KCC2-KCC4 cDNA constructs in cultured hippocampal neurons prepared from Sprague Dawley rat embryos and assaying neuronal Cl− through gramicidin perforated patch-clamp recordings. We found that when neurons had been transfected with a chimeric KCC2 that lacked the unique ISO domain, hyperpolarizing responses to GABA were abolished. This finding indicates that the ISO domain is required for neuronal Cl− regulation. Furthermore, we discovered that when KCC2 lacks the ISO domain, it still retains swelling-activated transport, which demonstrates that there are exclusive molecular determinants of isotonic and swelling-induced K+-Cl− cotransport in neurons.