Modulation of a transient outward current in serotonergic neurones by alpha 1-adrenoceptors.
The excitability of various neurones in the mammalian central nervous system (CNS), ranging from motoneurones to serotonergic neurones, is enhanced by alpha 1-adrenoceptor agonists. Excitations mediated via alpha 1-adrenoceptors are associated with a slow depolarization and an increase in input resistance, probably resulting from a decrease in resting potassium conductance. However, the involvement of voltage-dependent transient currents in mediating alpha 1 excitatory effects has not been evaluated. An early transient outward current has been described which is important in regulating the frequency of repetitive firing; it is activated by depolarizing voltage steps from potentials more negative than rest and blocked by 4-aminopyridine. This current, which has been termed 'IA', was found originally in invertebrates and subsequently in various vertebrate neurones. The present single-electrode voltage-clamp study demonstrates an early transient outward current (IA) in serotonergic neurones which is suppressed by noradrenaline and the alpha 1-agonist phenylephrine; a suppression of IA may account in part for the acceleration of pacemaker activity induced by alpha 1-agonists in serotonergic neurones.
Aghajanian
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D000818:Animals; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D004553:Electric Conductivity; D007473:Ion Channels / Q000502:physiology*; D007700:Kinetics; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000502:physiology*; D011224:Prazosin / Q000494:pharmacology; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000502:physiology*
D007473:Ion Channels; D011942:Receptors, Adrenergic, alpha; D002104:Cadmium; D010656:Phenylephrine; D012701:Serotonin; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin