A slow outward current activated by FMRFamide in heart interneurons of the medicinal leech

Farzan Nadim, Ronald L. Calabrese

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27 Scopus citations


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 (I(KF)), which has very slow activation and deactivation kinetics. Addition of physiologically measured amounts of I(KF) to the model two-cell oscillator can account for the acceleratory effect of FMRFamide.

Original languageEnglish (US)
Pages (from-to)4461-4472
Number of pages12
JournalJournal of Neuroscience
Issue number11
StatePublished - 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Neuroscience


  • FMRFamide
  • K
  • conductance-based model
  • leech
  • neural oscillator
  • slow outward currents


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