Serotonin differentially modulates two K+ currents in the Retzius cell of the leech.
The effects of 100 mumol l-1 serotonin (5-HT) were investigated on the Na+- and Ca2+-dependent action potential and distinct K+ currents in the Retzius (R) cells of the hirudinid leeches Macrobdella decora and Hirudo medicinalis by conventional current-clamp and two-microelectrode voltage-clamp techniques. 1. In normal Na+-containing Ringer, 5-HT decreased the duration of the action potential prolonged by 5 mmol l-1 tetraethylammonium (TEA+) chloride. 2. In Na+-free saline containing 25 mumol l-1 TEA+ to block IK, 5-HT reduced the amplitude and duration of Ca2+ spikes evoked by intracellular current injection. 3. Under voltage-clamp, 5-HT enhanced the peak amplitude of an early transient 4-aminopyridine (4-AP)-sensitive, voltage-dependent outward current, termed IA. A small but significant increase in the time constant of inactivation (tau off) of IA was also measured after exposure to 5-HT. 4. 5-HT suppressed the peak and steady-state amplitudes of a delayed TEA+-sensitive, voltage-dependent outward current, termed IK. These results demonstrate differential simultaneous modulation of distinct K+ currents in the Retzius cell of the leech by the endogenous transmitter serotonin. These cells contain and release 5-HT, and are believed to be multifunction neurons implicated in feeding and swimming. This modulation may change the excitable properties of the cell, leading to a negative feedback autoregulation of its transmitter output.
Acosta-Urquidi
J
J
Department of Neurology, Yale University School of Medicine, New Haven, CT 06510.
Sahley
C L
CL
Kleinhaus
A L
AL
D000200:Action Potentials / Q000187:drug effects; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005724:Ganglia / Q000166:cytology / Q000378:metabolism*; D007865:Leeches / Q000502:physiology*; D009474:Neurons / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects*; D012701:Serotonin / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000631:Aminopyridines; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D012701:Serotonin; D012964:Sodium; D002118:Calcium