GABA C receptor

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The GABA_C receptor is also linked to chloride channels, with distinct physiological and pharmacological properties. In contrast to the fast and transient responses elicited from GABA_A receptors, GABA_C receptors mediate slow and sustained responses. Pharmacologically, GABA_C receptors are bicuculline- and baclofen-insensitive, and are not modulated by many GABA_A receptor modulators (such as benzodiazepines and barbiturates and neuroactive steroids). The GABA_C receptors are activated by cis-aminocrotonic acid (CACA), which is not recognised by either the GABA_A or GABA_B receptors, suggesting that they recognise the partially folded conformation of GABA. GABA_C receptors, like GABA_A receptors are blocked by picrotoxin, while 1,2,5,6-tetrahydropyridine-4-yl methyl phosphinic acid (TPMPA) appears to inhibit GABA_C receptors selectively. However, molecular cloning studies have revealed that this pharmacological profile is remarkably similar. Like other ligand-gated ion channels, the molecule is probably formed by five subunits arranged around a central pore. Like the GABA_A channel, the pore, when open, is permeable to chloride ions, though its conductance is smaller than that of GABA_A. The genes for GABA_C are encoded on chromosome 6 in humans, distinct from the clusters of GABA_A receptor subunit genes which are found on chromosomes 4, 5, 15 and X.