Related Experiment Videos
FMRFamide modulates potassium currents in circadian pacemaker neurons of Bulla gouldiana
S Michel1, C Ehnert, K Schildberger
1Institut für Zoologie, Universität Leipzig, Talstrasse 33, D-04103 Leipzig, Germany. smichel@mednet.ucla.edu
Abstract:
The peptide FMRFamide (Phe-Met-Arg-Phe-NH(2)) is known to modulate the circadian pacemaker found in the eye of the marine snail Bulla gouldiana. In the present study, we investigated the cellular mechanisms underlying this modulation by examining the effects of FMRFamide on the membrane properties of the circadian pacemaker cells, known as basal retinal neurons in this preparation. Bath application of FMRFamide (0.1-1 microM) increased the membrane conductance, and hyperpolarized the membrane potential of these neurons. Next, perforated-patch recordings were used to demonstrate that FMRFamide reversibly increased the outward current amplitude due to an augmentation of a non-inactivating calcium-independent current. Reversal potential of the tail currents and its dependence on extracellular potassium concentration suggested potassium ions as the charge carrier for this current. The peptide-modulated outward current was blocked by 54% after bath application of the potassium channel blocker tetraethylammonium chloride and completely blocked by substituting cesium for intracellular potassium. Voltage dependence, activation kinetics and tail current kinetics of the FMRFamide-modulated current were consistent with values found for the delayed rectifier current.Overall, our data suggest that FMRFamide modulates a delayed rectifier potassium current and at least one other, less voltage-dependent conductance. This provides a mechanistic explanation for FMRFamide's ability to both shift the phase and attenuate light-induced phase shifts of the circadian pacemaker in B. gouldiana.
Insights
The peptide FMRFamide modulates snail eye circadian pacemaker cells by activating a potassium current. This peptide action explains how FMRFamide influences circadian rhythms and light responses.
Area of Science:
- Neuroscience
- Chronobiology
- Marine Biology
Background:
- The peptide FMRFamide is known to influence circadian rhythms in the marine snail Bulla gouldiana.
- The marine snail's eye contains a circadian pacemaker composed of basal retinal neurons.
Purpose of the Study:
- To investigate the cellular mechanisms by which FMRFamide modulates the circadian pacemaker cells.
- To examine the effects of FMRFamide on the membrane properties of basal retinal neurons.
Main Methods:
- Utilized perforated-patch recordings to study neuronal membrane properties.
- Applied FMRFamide and potassium channel blockers (tetraethylammonium chloride, cesium) to observe effects on neuronal currents.
- Analyzed reversal potentials and ion dependence to identify charge carriers.
Main Results:
- FMRFamide increased membrane conductance and hyperpolarized basal retinal neurons.
- The peptide augmented a non-inactivating, calcium-independent outward current, identified as a potassium current.
- This FMRFamide-modulated current exhibited characteristics of the delayed rectifier potassium current.
Conclusions:
- FMRFamide modulates a delayed rectifier potassium current and another conductance in snail circadian pacemaker cells.
- This action provides a cellular mechanism for FMRFamide's effects on circadian phase shifting and light responses.
- The findings offer insights into the neurochemical regulation of circadian pacemakers in invertebrates.