Journal of Neuroscience, Vol 6, 252-259, Copyright © 1986 by Society for Neuroscience
Analysis of FMRF-amide effects on Aplysia bursting neurons
P Ruben, JW Johnson and S Thompson
The peptide L-phenylalanyl-L-methionyl-L-arginyl-L-phenylalaninamide
(FMRF-amide) was pressure-applied onto the somata of bursting neurons L4
and L6 in the Aplysia abdominal ganglion. FMRF-amide causes a biphasic
response, first depolarizing and then hyperpolarizing the neuron. In
voltage-clamp experiments, FMRF-amide induces an inward current that begins
100-200 msec after applying the peptide and peaks in 2-10 sec. This is
followed by an outward current that begins with a latency of 2-5 sec and
peaks in 15-65 sec. The entire response lasts 1- 5 min. Experiments were
done to separate the two currents induced by FMRF-amide on the basis of ion
selectivity and kinetics and to determine their I(V) relationships. The
currents were studied using a method to quickly measure I(V) curves. The
inward current is caused by a conductance increase and has a reversal
potential of approximately +18 mV. This current depends on the
concentration of extracellular Na ions but not Ca, Cl, or K ions and is
insensitive to tetrodotoxin, hexamethonium, and curare. The outward current
is caused by a conductance increase and has a reversal potential of
approximately -61 mV, which is similar to the reversal potential of the
fast, transient K current (IA) in the same cells. This current is sensitive
to changes in the external K ion concentration but not to changes in Cl,
Ca, or Na concentration. The outward current is partially blocked by 1 mM
4- aminopyridine but not TEA or curare. Neither current is significantly
voltage dependent within the range from -70 to -40 mV.(ABSTRACT TRUNCATED
AT 250 WORDS)