Summary
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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.
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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.
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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.
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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.
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References
Acosta-Urquidi, J. (1985). Calcium and cyclic AMP-mediated regulation of Ca and K-currents inHermissenda giant neurons.Soc. Neurosci. Abstr. 11788.
Benson, J., and Levitan, I. (1983). Serotonin increases an anomalously rectifying K+ current inAplysia neuron R15.Proc. Natl. Acad. Sci. USA 803522–3525.
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.
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. USA 817642–7646.
Ewald, D., and Eckert, R. (1983). Cyclic AMP enhances calcium dependent potassium current inAplysia neurons.Cell. Mol. Neurobiol. 3345–353.
Gorman, A., and Thomas, M. (1980). Potassium conductance and internal calcium accumulation in a molluscan neurone.J. Physiol. (Lond.)308287–313.
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.
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.
Jerussi, T., and Alkon, D. (1981). Ocular and extraocular responses of identified neurons in pedal ganglia ofHermissenda crassicornis.J. Neurophysiol. 46659–671.
Klein, M., and Kandel, E. R. (1980). Mechanism of calcium current modulation underlying presynaptic facilitation and behavioral sensitization inAplysia.Proc. Natl. Acad. Sci. USA 776912–6916.
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. USA 795713–5717.
Paupardin-Tritsch, D., Deterre, P., and Gerschenfeld, H. (1981). Relationship between two voltage-dependent serotonin responses of molluscan neurones.Brain Res. 217201–206.
Pellmar, T. (1984). Enhancement of inward current by serotonin in neurons ofAplysia.J. Neurobiol. 15 13–25.
Pellmar, T., and Carpenter, D. (1980). Serotonin induces a voltage-sensitive calcium current in neurons ofAplysia californica.J. Neurophysiol. 44423–439.
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.Nature 313392–395.
Siegelbaum, S., Camardo, J., and Kandel, E. (1982). Serotonin and cyclic AMP close single K+ channels inAplysia sensory neurons.Nature 299413–417.
Tillotson, D. (1979). Inactivation of Ca conductance dependent on entry of Ca ions in molluscan neurons.Proc. Natl. Acad. Sci. USA 761497–1500.
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Jacklet, J.W., Acosta-Urquidi, J. Serotonin decreases a background current and increases calcium and calcium-activated current in pedal neurons ofHermissenda . Cell Mol Neurobiol 5, 407–412 (1985). https://doi.org/10.1007/BF00755404
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DOI: https://doi.org/10.1007/BF00755404