Skip to main content
NCBI home page
Cellular and Molecular Neurobiology logoLink to Cellular and Molecular Neurobiology
. 1985 Dec;5(4):407–412. doi: 10.1007/BF00755404

Serotonin decreases a background current and increases calcium and calcium-activated current in pedal neurons ofHermissenda

Jon W Jacklet 1,2, Juan Acosta-Urquidi 3
PMCID: PMC11572821  PMID: 4084949

Abstract

  1. The effects of serotonin (5-HT) on membrane potential, membrane resistance, and select ionic currents were examined in large pedal neurons (LP1, LP3) of the molluskHermissenda.

  2. Calcium (Ca) action potentials were evoked in sodium-free artificial seawater containing tetramethylammonium, tetraethylammonium, and 4-aminopyridine (0-Na, 4-AP, TEA ASW). They failed at stimulation rates greater than 0.5/sec and were blocked by cadmium (Cd). Under voltage clamp the calcium current (I Ca) responsible for them also failed with repeated stimulation. Thus,I Ca inactivation accounts for refractoriness of the Ca action potential.

  3. The addition of 10µM 5-HT to 0-Na, 4-AP, TEA ASW produced a slight depolarization and increased excitability and input resistance. Under voltage clamp the background current decreased. The voltage-dependent inward, late outward, and outward tail currents, sensitive to Cd, increased.I Ca inactivation persisted.

  4. Under voltage clamp with Ca influx blocked by Cd, the addition of 10µM 5-HT decreased the remaining current uniformly over membrane potentials of — 10 to — 100 mV. Thus, 5-HT reduces a background current that is active within the physiological range of the membrane potential, voltage insensitive, independent of Ca influx, noninactivating, and not blocked by 4-AP or TEA.

Key words: serotonin, background current, calcium current, calcium-activated current, calcium inactivation, molluscan neurons

References

  1. Acosta-Urquidi, J. (1985). Calcium and cyclic AMP-mediated regulation of Ca and K-currents inHermissenda giant neurons.Soc. Neurosci. Abstr.11788. [Google Scholar]
  2. Benson, J., and Levitan, I. (1983). Serotonin increases an anomalously rectifying K+ current inAplysia neuron R15.Proc. Natl. Acad. Sci. USA803522–3525. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Boyle, M., and Smith, S. (1982). Increase in intracellular Ca accompanying a serotonin-induced reduction of outward current in identified neurons ofHelix aspersa.Soc. Neurosci. Abstr.8523. [Google Scholar]
  4. Boyle, M., Klein, M., Smith, S., and Kandel, E. (1984). 5-HT increases intracellular Ca2+ transient in voltageclamped sensory neurons ofAplysia californica.Proc. Natl. Acad. Sci. USA817642–7646. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Ewald, D., and Eckert, R. (1983). Cyclic AMP enhances calcium dependent potassium current inAplysia neurons.Cell. Mol. Neurobiol.3345–353. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Gorman, A., and Thomas, M. (1980). Potassium conductance and internal calcium accumulation in a molluscan neurone.J. Physiol. (Lond.)308287–313. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Jacklet, J., Acosta-Urquidi, J., and Alkon, D. (1983). Neuron LP1 ofHermissenda: Electrophysiology and effects of dopamine, 5-HT and cAMP.Soc. Neurosci. Abstr.9506. [Google Scholar]
  8. Jacklet, J., Acosta-Urquidi, J., and Alkon, D. (1984). Inward current and calcium dependent potassium current are increased and other potassium current decreased by serotonin in pedal neurons ofHermissenda.Soc. Neurosci. Abstr.10145. [Google Scholar]
  9. Jerussi, T., and Alkon, D. (1981). Ocular and extraocular responses of identified neurons in pedal ganglia ofHermissenda crassicornis.J. Neurophysiol.46659–671. [DOI] [PubMed] [Google Scholar]
  10. Klein, M., and Kandel, E. R. (1980). Mechanism of calcium current modulation underlying presynaptic facilitation and behavioral sensitization inAplysia.Proc. Natl. Acad. Sci. USA776912–6916. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Klein, M., Camardo, J., and Kandel, E. R. (1982). Serotonin modulates a specific potassium current in sensory neurons that show presynaptic facilitation inAplysia.Proc. Natl. Acad. Sci. USA795713–5717. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Paupardin-Tritsch, D., Deterre, P., and Gerschenfeld, H. (1981). Relationship between two voltage-dependent serotonin responses of molluscan neurones.Brain Res.217201–206. [DOI] [PubMed] [Google Scholar]
  13. Pellmar, T. (1984). Enhancement of inward current by serotonin in neurons ofAplysia.J. Neurobiol.15 13–25. [DOI] [PubMed] [Google Scholar]
  14. Pellmar, T., and Carpenter, D. (1980). Serotonin induces a voltage-sensitive calcium current in neurons ofAplysia californica.J. Neurophysiol.44423–439. [DOI] [PubMed] [Google Scholar]
  15. Shuster, M., Camardo, J., Siegelbaum, S., and Kandel, E. (1985). Cyclic AMP-dependent protein kinase closes the serotonin-sensitive K+ channels ofAplysia sensory neurones in cell-free membrane patches.Nature313392–395. [DOI] [PubMed] [Google Scholar]
  16. Siegelbaum, S., Camardo, J., and Kandel, E. (1982). Serotonin and cyclic AMP close single K+ channels inAplysia sensory neurons.Nature299413–417. [DOI] [PubMed] [Google Scholar]
  17. Tillotson, D. (1979). Inactivation of Ca conductance dependent on entry of Ca ions in molluscan neurons.Proc. Natl. Acad. Sci. USA761497–1500. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Cellular and Molecular Neurobiology are provided here courtesy of Springer

RESOURCES