An unusual low-current receptor-circuit in the trap setae of the prey-capture apparatus ofLoricera pilicornis (Carabidae,Coleoptera)

Summary The antennal trap setae ofLoricera pilicornis (Carabidae) with one mechanoreceptive neuron and 2 or 3 neurons of so far unknown function were characterized electrophysiologically. The setal shaft is conductive, but screens the epithelial cells against electrolytes (5 mM KCl, 200 mM CaCl₂).Transepithelial resistances in the setae ranged from 180 to 490 M (25° C) and 320 to 830 M (12° C). Mechanical stimuli reduce the transepithelial voltage by maximally –13 mV (receptor potential), corresponding to (calculated) receptor currents below 30 pA. Spikes superimposed on receptor potentials can be 20 mV p/p and cause transient transeptithelial current changes that exceed the receptor current.Clamp currents greater than 110 pA inward (12° C) across the epithelium elicit positive spikes at frequencies that are essentially independent of current intensity. Outward clamp currents above 25 pA elicit negative spikes of current-dependent frequency with one to three positive smaller pulses superimposed on them. This indicates the coexistance of apical and basal spike generator sites in the sensillar neurons.We conclude: in the cell with the tubular body, mechanical stimuli elicit a receptor current and apical spikes. These spikes can render the receptor lymph cavity sufficiently negative to trigger synchronized apical spikes in the other neurons, too. The apical spikes trigger the less synchronized basal spikes in the individual neurons.Abbreviations TEV transepithelial voltage - TER transepithelial resistance