Serotonin enhances a low-voltage-activated calcium current in rat spinal motoneurons.
Calcium currents and the effects of 5-HT on these currents were investigated in visually identified motoneurons using whole-cell recording in the neonatal rat spinal cord slice preparation. In current-clamp recording, step depolarizations from a holding potential of about -90 mV produced a low-threshold transient depolarizing response and a high-threshold long-lasting spike. In voltage-clamp recording, low (LVA) and high (HVA) voltage-activated Ca2+ currents were recorded in response to depolarizing voltage steps. Low concentration of Cd2+ (50 microM) did not reduce the amplitude of the LVA current but markedly diminished the HVA current. Bath application of 5-HT (10-50 microM) markedly increased the amplitude of the LVA current without causing a shift in the current (I)-voltage (V) relation. In contrast, 5-HT did not appreciably affect the amplitude of the HVA current. We conclude that 5-HT specifically enhances the LVA Ca2+ current and that this effect together with the previously reported 5-HT-induced inward current (Takahashi and Berger, 1990), would facilitate the excitation of motoneurons.
Berger
A J
AJ
Department of Physiology, Kyoto University Faculty of Medicine, Japan.
Takahashi
T
T
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002413:Cations, Divalent / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D007552:Isotonic Solutions / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000494:pharmacology*; D013116:Spinal Cord / Q000166:cytology / Q000502:physiology*
D002413:Cations, Divalent; D007552:Isotonic Solutions; C051865:Krebs-Ringer solution; D012701:Serotonin; D002118:Calcium