Pharmacological investigation of protein kinase C- and cGMP-dependent ion channels in cultured olfactory receptor neurons of the hawkmoth Manduca sexta.
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.
Dolzer
Jan
J
Department of Biology, Animal Physiology, Philipps-University of Marburg, Karl-von-Frisch-Strasse 8, Marburg D-35032, Germany.
Krannich
Steffi
S
Stengl
Monika
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism*; D004594:Electrophysiology; D007473:Ion Channels / Q000378:metabolism*; D018402:Manduca / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018034:Olfactory Receptor Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D007473:Ion Channels; D011493:Protein Kinase C; D006152:Cyclic GMP; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium