Figure 8
B. annulata venom contains an agonist of GABAA receptors. (a) Traces on the left illustrate inward current responses in Xenopus oocytes expressing the neuronal GABAA (α1β2γ2) receptor; cells were held at − 60 mV and superfused with either GABA (10 μM; black trace) or AE (1 mg ml−1; orange trace). In the trace on the right, AE was applied close to the oocyte surface using the jet delivery method, which consists of a small volume (25–75 nl) ejected from a micropipette filled with solution containing AE (0.5 mg ml−1), four AE-jets (orange arrows) applied successively show that current responses generated were robust and reproducible. (b) Top traces show that native oocytes (H2O-injected) were not sensitive to GABA superfusion or to AE jet-delivery (orange arrow indicates jet activation), while oocytes from the same frog expressing the neuronal GABAA receptor (bottom traces) generated robust current responses to both GABA and AE. (c) Traces are responses at different holding potentials from − 100 to + 40 mV elicited either by jets of AE or NE as indicated; the graph is the current–voltage relationship of the responses by AE applying the same protocol in 6 different oocytes (2 frogs); individual data points are the mean ± S.D. of the peak current response in each potential. (d,e) AE (and NE) affects two more GABAA receptor types expressed in oocytes, the oligodendroglial receptor α3β2γ1 (red traces) and the homomeric ρ1 receptor (green traces). Traces in (d) show the current response to GABA around the concentration threshold for each receptor, 1 μM for α3β2γ1 and 10 nM for the ρ1 receptor. In (e) the traces on the left illustrate responses elicited by a maximal concentration of GABA in oocytes expressing the α3β2γ1 receptor (in red) or the ρ1 receptor (trace in green), while the traces to the right show the response in the respective oocytes elicited by the same dose of AE. Traces are representative of results obtained in 7 oocytes from 3 different frogs.
