Fig. 6. Effects of agonists and antagonists for various GABA receptor subtypes on the membrane potential (V_m) changes evoked by salivary duct nerve (SDN)-stimulation. Asterisks mark the timepoints of stimulation (5 V, 0.2 ms, 5 Hz, 2 s trains). The duration of drug application is indicated by bars. (A,B) Application of SKF97541 or baclofen mimic the GABA-induced enhancement in the electrical responses. (C,D) CGP52432 and CGP54626 suppress the GABA-induced enhancement. (E) The GABA_BR antagonist CGP52432 suppresses the SKF97541-induced enhancement. (F) Bicuculline-induced augmentation of electrical responses of acinar cells to SDN-stimulation. (G) Bar chart for the effects of all tested drugs. The gray dotted line indicates the control amplitude (=100%) induced by electrical SDN-stimulation in the absence of GABA and other drugs. The number of replicates for each bar is stated in parentheses. The bars show means±s.e.m. Muscimol (GABA_AR agonist), picrotoxin (GABA_AR antagonist), THIP (GABA_CR antagonist and partial GABA_AR agonist) and TPMPA (GABA_CR antagonist) did not affect the control amplitudes or the GABA-induced enhancement. The GABA_BR-specific agonists SKF97541 and baclofen enhanced the acinar cell response amplitudes. The GABA_BR antagonists CGP54626 and CGP52432 suppressed the GABA-induced enhancement. Bicuculline also enhanced the cell responses to SDN-stimulation. The mean amplitude of at least two stimulations during GABA-bath application and/or drug treatment was normalized to the mean amplitude of at least two consecutive control stimulations for each experiment. The data were analyzed by applying one-way analysis of variance and Tukey's post test. ^*P<0.05, ^**P<0.001.