Three austin family compounds from Penicillium brasilianum exhibit selective blocking action on cockroach nicotinic acetylcholine receptors

Austin (AT) and its derivatives (dehydroaustin (DAT) and acetoxydehydroaustin (ADAT)) produced by Penicillium brasilianum MG-11 exhibit toxicity to insects, yet their targets are unknown. Here, we used whole-cell patch-clamp electrophysiology to investigate the action of AT family compounds on cockroach acetylcholine (ACh), γ-aminobutyric acid (GABA) and l-glutamate receptors expressed in the American cockroach (Periplaneta americana) neuron. U-tube application of AT or its derivatives did not induce any current amplitudes, suggesting that they did not act as agonist of these three receptors. In the second step of experiments, they were bath-applied for 1 min before co-application with the corresponding ligand. We found that AT and its derivatives had no effect on GABA and l-glutamate-induced currents, whereas they significantly reduced ACh- and epibatidine-induced currents, showing that these compounds acted as selective antagonists of nicotinic acetylcholine receptors (nAChRs) expressed in the cockroach neuron. Of the compounds, DAT showed the highest blocking potency for nAChRs, differentially attenuating the peak and slowly desensitizing current amplitude of ACh-induced responses with pIC50 (= −log IC50 (M)) values of 6.11 and 5.91, respectively. DAT reduced the maximum normalized response to ACh without a significant shift in EC50, suggesting that the blocking action is not competitive with ACh.