Journal of Neuroscience, Vol 8, 3200-3207, Copyright © 1988 by Society for Neuroscience
Inward rectification in response to FMRFamide in Aplysia neuron L2: summation with transient K current
S Thompson and P Ruben
Hopkins Marine Station of Stanford University, Pacific Grove, California 93950.
The response of Aplysia abdominal ganglion neuron L2 to the molluscan
neuroactive peptide Phe-Met-Arg-Phe-NH2 (FMRFamide) was studied in
voltage-clamp experiments. In all of the experiments, focal application of
the peptide to the soma activated an inward rectifier current and reduced
the apparent amplitude of the transient K current, IA. In a few cells, Na
and K currents were activated in addition to these effects. Voltage-jump
experiments were performed to study the ionic dependence, kinetics, and
voltage dependence of the inward rectifier. Inward rectification increased
exponentially during hyperpolarizing pulses and recovered exponentially on
return to the resting potential. The reversal potential was variable, but
was near -40 mV at the beginning of experiments. Inward rectification was
insensitive to changes in external Na, Ca, or K concentration, but lowering
the external Cl concentration had complicated effects on current amplitude.
When KCl microelectrodes were used, perfusion with low-Cl external saline
increased the amplitude of the peptide-dependent inward rectifier and
shifted its reversal potential to a more positive voltage. With KAc
microelectrodes, perfusion with low-Cl saline reduced the amplitude of the
current. Inward rectification increased when a KAc microelectrode was
withdrawn and replaced with a low-resistance KCl electrode, even when there
was no measurable change in reversal potential. These results suggest that
the FMRFamide-dependent inward rectifier is a Cl current that, like the
current described by Chesnoy-Marchais (1982, 1983), is modulated by
intracellular Cl. FMRFamide reduced the apparent amplitude of IA without
affecting the voltage dependence of IA activation or inactivation.(ABSTRACT
TRUNCATED AT 250 WORDS)