Analysis of the modulation by serotonin of a voltage-dependent potassium current in sensory neurons of Aplysia.
Potassium currents in pleural sensory neurons of Aplysia were studied under control conditions and in the presence of serotonin (5-HT). Using pharmacological techniques we isolated a current that we refer to as IK,V. Although it is not known whether IK,V represents a distinct type of membrane channel, we described its properties using a Hodgkin-Huxley type model. The effects of 5-HT on IK,V were complex. 5-HT decreased by 50% the steady-state magnitude (Iss) of IK,V in response to a voltage-clamp pulse from -50 mV to +20 mV. In addition, 5-HT significantly slowed both activation kinetics (the time constant of activation was increased by 29% at +20 mV) and inactivation kinetics (the time constant of inactivation was increased by 518% at +20 mV). Mathematical descriptions of IK,V in control conditions and in the presence of 5-HT were used to estimate the relative contribution of serotonergic modulation of IK,V to the total 5-HT-induced modulation of membrane currents. Effects of 5-HT on IK,V account for more than 87% of the 5-HT-induced reduction in outward current during the first 20 ms of a voltage-clamp pulse to +20 mV. This result implies that 5-HT exerts many of its effects on spike width in sensory neurons via modulation of IK,V. Effects of 5-HT on IK,V are consistent with a model in which the maximal conductance underlying the current is decreased by 50%, and the rate constants between open and closed states of both the activation and inactivation processes are diminished in magnitude across all membrane potentials.
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225.
J A
JA
White
D A
DA
Baxter
J H
JH
Byrne
D000818:Animals; D001048:Aplysia; D055592:Biophysical Phenomena; D001703:Biophysics; D004553:Electric Conductivity; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D009475:Neurons, Afferent / Q000187:drug effects* / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000494:pharmacology*
D015221:Potassium Channels; D012701:Serotonin; D011188:Potassium