Diverse voltage-sensitive dyes modulate GABA_A receptor function

Voltage-sensitive dyes are important tools for assessing network and single-cell excitability, but an untested premise in most cases is that the dyes do not interfere with the parameters (membrane potential, excitability) that they are designed to measure.Wefound that popular members of several different families of voltage-sensitive dyes modulate GABA_A receptor with maximum efficacy and potency similar to clinically used GABA_A receptor modulators. Di-4-ANEPPS and DiBAC4(3) potentiated GABA function with micromolar and high nano-molar potency, respectively, and yielded strong maximum effects similar to barbiturates and neurosteroids. Newer blue oxonols had biphasic effects on GABA_A receptor function at nanomolar and micromolar concentrations, with maximum potentiation comparable to that of saturating benzodiazepine effects. ANNINE-6 and ANNINE-6plus had no detectable effect on GABA_A receptor function. Even dyes with no activity on GABA_A receptors at baseline induced photodynamic enhancement of GABA_A receptors. The basal effects of dyes were sufficient to prolong IPSCs and to dampen network activity in multielectrode array recordings. Therefore, the dual effects of voltage-sensitive dyes on GABAergic inhibition require caution in dye use for studies of excitability and network activity.