Ionic mechanism of a hyperpolarizing 5-hydroxytryptamine effect on leech neuropile glial cells.
The ionic mechanism of a membrane effect of 5-hydroxytryptamine (5-HT) on neuropile glial (NG) cells in ganglia of the medicinal leech was investigated with conventional single-barrelled microelectrodes. Control experiments were made with double-barrelled ion-selective microelectrodes. 5-Hydroxytryptamine hyperpolarized the NG-cell membrane and increased the conductance considerably. Methysergide, a potent 5-HT antagonist, blocked the 5-HT-induced hyperpolarization completely. When leech ganglia were superfused with physiological bathing media free of 5-HT, the NG-cell membrane conductance returned to the original value, but the membrane potential recovered only partially from the hyperpolarization in most experiments. In glial membranes artificially depolarized by means of constant-current injection, the amplitude of the 5-HT response increased. The amplitude decreased with membrane hyperpolarization and reversed at - 73 mV, close to the potassium equilibrium potential. The reversal potential changed by 52 mV when the extracellular potassium concentration was altered by a factor of 10. We conclude that 5-HT increases the potassium conductance of NG-cell membranes.
D000818:Animals; D002027:Bufotenin / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D005724:Ganglia / Q000187:drug effects / Q000502:physiology*; D007865:Leeches; D008564:Membrane Potentials / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*
D002027:Bufotenin; D012701:Serotonin; D011188:Potassium