CHO cells stably expressing GABA_B receptors are sensitive and reliable GABA biosensors.

<p>Biosensors were loaded with Fura 2 and Ca²⁺ mobilization was measured in response to bath-applied GABA. <b>A,</b> Concentration-response relationships for GABA (symbols show mean ± s.e.m., N = 14 cells). <b>B,</b> Representative traces from a GABA biosensor showing that the biosensors do not respond to KCl depolarization (↓, KCl) or taste stimulation with a sweet/bitter mixture (↓, taste), and only minimally to acetic acid (↓, HAc). GABA-evoked Ca²⁺ responses (↓, GABA) were unaffected by removing extracellular Ca²⁺ (“0 Ca”, throughout the shaded area). Lastly, CGP55845 (“CGP”, 10 µM, present throughout the shaded area) reversibly blocked GABA-elicited biosensor responses. GABA, 100 nM; KCl, 50 mM. <b>C,</b> Representative traces from a GABA biosensor showing that biosensors respond to either GABA (100 nM) or ATP (10 µM), but CGP55845 (10 µM, present throughout the shaded area) only blocks responses elicited by GABA. <b>D,</b> Summary of data as shown in C. N = 6; ***, <i>p</i><0.001, Student <i>t</i>-test.