Differential modulation of voltage-dependent currents in Hermissenda type B photoreceptors by serotonin.
1. In identified photoreceptors in the eyes of Hermissenda, serotonin (5-HT) enhances the peak and plateau phases of light-evoked generator potentials and modulates light-dependent and voltage-dependent currents. In addition, electrophysiological and morphological studies indicate that 5-HT may contribute to cellular plasticity detected in the visual system of Hermissenda produced by classical conditioning procedures. With the use of conventional two-electrode voltage-clamp techniques, we examined the effects of 5-HT on three distinct currents recorded across the soma membranes of identified lateral and medial type B photoreceptors in the isolated circumesophageal nervous system. 2. The inward rectifier (Iir), a putative K(+)-dependent conductance, activates in 0-Na artificial seawater at membrane potentials greater than -60 mV, is voltage dependent, noninactivating, and reaches steady-state within 800 ms to 3 s at -100 mV. Bath application of 10(-4) M 5-HT consistently enhanced the magnitude of Iir at all potentials tested (-60 to -100 mV) and, in some cases, allowed expression of Iir, which was not initially detectable before the application of 5-HT. 3. The major component of outward K+ current in type B photoreceptors with IA and IK(Ca) blocked is the delayed rectifier [IK(v)]. 5-HT (10(-4) M) produced both an increase as well as a decrease in the peak amplitude of IK(v) and consistently slowed its inactivation rate and reduced twin-pulse inactivation. 4. A previously identified outward K+ current in type B photoreceptors has properties that are similar to the A current (IA).(ABSTRACT TRUNCATED AT 250 WORDS)
Acosta-Urquidi
J
J
Department of Neurobiology and Anatomy, University of Texas Medical School, Houston 77225.
Crow
T
T
D000818:Animals; D001369:Axons / Q000502:physiology; D017952:Ganglia, Invertebrate / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D008974:Mollusca; D009474:Neurons / Q000502:physiology; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology; D012701:Serotonin / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*
D015221:Potassium Channels; D012701:Serotonin