Pharmacological Investigation of Protein Kinase C- and cGMP Dependent Ion Channels in Cultured Olfactory Receptor Neurons of the Hawkmoth Manduca sexta

摘要

In the hawkmoth Manduca sexta, pheromone stimuli of different strength and duration rise the intracellular Ca~(2+) 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 Ca~(2+)-, PKC-, and cGMP-dependent ion channels. Stepping to positive holding potentials in high intracellular Ca~(2+) elicits different Ca~(2+)-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.