Modulation of ionic currents in Aplysia motor neuron B15 by serotonin, neuropeptides, and second messengers.
Both 5-HT and the 9 amino acid neuropeptide SCPb modulate 3 ionic currents in B15, enhancing a voltage-dependent inward sodium current, decreasing an outward potassium current and increasing an inward rectifying potassium current. In contrast, FMRFamide decreases a voltage-dependent inward sodium current and increases an outward potassium current. We have also investigated the roles of several second-messenger systems that may be mediating the effects of these modulators. Bath application of membrane permeable analogs of cAMP enhance the voltage-dependent inward sodium current and both 5-HT and SCPb increase cAMP levels in B15, suggesting that cAMP may be mediating part of the observed effects of these transmitters on B15. Experiments with phorbol ester, a protein kinase inhibitor, and a phospholipase inhibitor suggest that the phospholipase C/protein kinase C cascade may decrease an outward potassium current. Thus, 5-HT and SCPb may activate multiple second-messenger systems to modulate 3 ionic currents in B15. Additional studies suggest that a cascade involving arachidonic acid may be involved in mediating part of the FMRFamide responses in B15. These studies are beginning to define molecular mechanisms whereby a neuron differentially modulates multiple ionic currents in response to distinct chemical messengers.
Taussig
R
R
Department of Biological Sciences, Stanford University, California 94305.
Sweet-Cordero
A
A
Scheller
R H
RH
D000818:Animals; D001048:Aplysia / Q000502:physiology*; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology; D004789:Enzyme Activation; D019835:FMRFamide; D007473:Ion Channels / Q000187:drug effects*; D009046:Motor Neurons / Q000378:metabolism*; D009479:Neuropeptides / Q000494:pharmacology*; D010740:Phospholipases / Q000502:physiology; D015221:Potassium Channels / Q000187:drug effects; D011493:Protein Kinase C / Q000378:metabolism; D015290:Second Messenger Systems; D012701:Serotonin / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects
D001095:Arachidonic Acids; D007473:Ion Channels; D009479:Neuropeptides; D015221:Potassium Channels; D015222:Sodium Channels; D016718:Arachidonic Acid; D012701:Serotonin; D019835:FMRFamide; C041307:small cardioactive peptide B; D000242:Cyclic AMP; D011493:Protein Kinase C; D010740:Phospholipases