Chemical Senses Advance Access originally published online on July 16, 2008
Chemical Senses 2008 33(9):803-813; doi:10.1093/chemse/bjn043
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Pharmacological Investigation of Protein Kinase C- and cGMP-Dependent Ion Channels in Cultured Olfactory Receptor Neurons of the Hawkmoth Manduca sexta
1 Department of Biology, Animal Physiology, Philipps-University of Marburg, Karl-von-Frisch-Strasse 8, Marburg D-35032, Germany 2 Institute of Biology, Animal Physiology, University of Kassel, Heinrich-Plett-Strasse 40, Kassel D-34132, Germany
Correspondence to be sent to: Monika Stengl, Department of Biology, Animal Physiology, Philipps-University of Marburg, Karl-von-Frisch-Strasse 8, Marburg D-35032, Germany. e-mail: stengl{at}staff.uni-marburg.de
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Abstract |
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In the hawkmoth Manduca sexta, pheromone stimuli of different strength and duration rise the intracellular Ca2+ concentration in olfactory receptor neurons (ORNs). While second-long pheromone stimuli activate protein kinase C (PKC), which apparently underlies processes of short-term adaptation, minute-long pheromone stimuli elevate cyclic guanosine monophosphate (cGMP) concentrations, which correlates with time courses of long-term adaptation. To identify ion channels involved in the sliding adjustment of olfactory sensitivity, inside-out patch clamp recordings on cultured ORNs of M. sexta were performed to characterize Ca2+-, PKC-, and cGMP-dependent ion channels. Stepping to positive holding potentials in high intracellular Ca2+ elicits different Ca2+-dependent ion channels, namely small-conductance channels (2–20 ps), medium-conductance channels (20–100 ps), and large-conductance channels (>100 ps). Ion channels of 40, 60, and 70 ps opened after PKC activation, whereas 10- and >100-ps channels were observed less frequently. Application of 8-bromo cyclic guanosine monophosphate opened 55- and 70-ps channels and increased the open probability of >100-ps channels, whereas even in the presence of phorbol ester 40-ps channels were inhibited. Thus, cGMP elevations activate a different set of ion channels as compared with PKC and suppress at least one PKC-dependent ion channel.
Key words: insect olfactory transduction, ion channels, Manduca sexta, olfactory adaptation, patch clamp
Accepted 19 June 2008
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