Fig. 4. Sample current and fluorescence recordings from the α1L127Cβ2γ2 receptor labeled with A5m. Receptors were expressed in Xenopus  oocytes, and studied with two-electrode voltage clamp.30(A ) Exposure to γ-aminobutyric acid (GABA) elicits an inward current response (I) and an increase in fluorescence intensity (ΔF), suggesting that the environment around the fluorophore becomes more hydrophobic during channel activation. Channel desensitization does not affect fluorescence changes. (B ) Exposure to the competitive antagonist gabazine does not activate the receptor but elicits fluorescence change (ΔF). For comparison, responses to GABA from the same cell are also shown. (C ) Activation by GABA but not pentobarbital induces ΔF. Both sets of traces are from the same cell. (D ) Relationship between current and fluorescence change. The responses are normalized to those to GABA. The normalized ΔF is plotted as a function of normalized current response. P4S = piperidine-4-sulfonic acid; THIP = 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol; 3α5αP = allopregnanolone; ETO = etomidate; β-Ala = β-alanine, PB = pentobarbital. A , C , and D  are reproduced with permission from the British Journal of Pharmacology.30