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Y Pan, P Khalili, H Qian; Pharmacological Profile of Homomeric and Heteromeric GABA Receptors . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3783.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Recent studies indicate that the native GABAC receptors on retinal neurons are formed by heteromeric GABA ρ subunits. However, the properties and the assembly mechanisms of these heteromeric GABAC receptors are yet to be fully determined. In this study, we examined the characteristics of the responses elicited by various pharmacological agents on the homomeric and heteromeric GABA ρ receptors. Methods: Capped RNAs were synthesized from cloned white perch GABA ρ subunits. Xenopus oocytes were injected with either individual ρ subunit, or equal mixtures of two ρ subunits (each of ρ1 and ρ2 family). Two-electrode voltage-clamp techniques were used to monitor the membrane currents elicited from oocytes. Results: We examined the properties of the receptors formed in Xenopus oocytes by four white perch ρ subunits (ρ1A, ρ1B, ρ2A and ρ2B). The homomeric ρ receptors could be activated by a range of pharmacological agents (ß-alanine, I4AA, taurine and glycine), and exhibit distinct pharmacological profiles for the receptors formed by each perch ρ subunit. Specifically, when normalized to the maximum currents activated by GABA, the responses elicited by these agents were consistently smaller on the A-form receptors than those elicited from the B-form receptors. In addition, ß-alanine activates a larger conductance on the ρ1A receptor than those on the ρ2A receptors. On the other hand, heteromeric receptors were formed on oocytes injected with a mixture of ρ subunits, as the pharmacological responses observed on these cells differ significantly from those constituted by a simple combination of homomeric receptors. Moreover, the GABA off-responses elicited from the oocytes expressing mixed subunits could be fitted by a single exponential function, providing additional support for the heteromeric ρ receptors formation. Conclusion: Our results show heteromeric receptors could be formed among four white perch GABA ρ subunits with properties that differ from those of the homomeric ρ receptors.
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