A slow outward current activated by FMRFamide in heart interneurons of the medicinal leech.
The endogenous neuropeptide FMRFamide (Phe-Met-Arg-Phe-NH2) can accelerate the oscillation of reciprocally inhibitory pairs of interneurons that pace heartbeat in the medicinal leech. A model based on all available biophysical data of a two-cell heart interneuron oscillator provides a theoretical basis for understanding this modulation. Previously observed modulation of K+ currents by FMRFamide cannot account for this acceleratory effect in the model. This observation prompted the present reexamination of K+ currents in heart interneurons. We devised better methods for separation of the various components of K+ current and more accurately measured their activation and deactivation kinetics. Moreover, we demonstrated that FMRFamide activates a previously undetected K+ current (IKF), which has very slow activation and deactivation kinetics. Addition of physiologically measured amounts of IKF to the model two-cell oscillator can account for the acceleratory effect of FMRFamide.
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Department of Biology, Emory University, Atlanta, Georgia 30322, USA.
Calabrese
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D000818:Animals; D004553:Electric Conductivity; D004594:Electrophysiology; D019835:FMRFamide; D006321:Heart / Q000294:innervation; D007395:Interneurons / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D007447:Invertebrate Hormones / Q000494:pharmacology; D007700:Kinetics; D007865:Leeches / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008959:Models, Neurological; D009479:Neuropeptides / Q000494:pharmacology*; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010507:Periodicity; D015221:Potassium Channels / Q000502:physiology
D007447:Invertebrate Hormones; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D015221:Potassium Channels; D019835:FMRFamide