Program of the 2001 International Worm Meeting - Sternberg Lab ...

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48. SLO-1 Potassium Channel
Regulates Duration of
Neurotransmitter Release
Zhao-Wen Wang, Owais Saifee,
Michael L. Nonet, Lawrence Salkoff
Department of Anatomy and Neurobiology,
Washington University School of Medicine,
Campus Box 8108, 660 S. Euclid Avenue, St.
Louis, MO 63110
In order to identify negative regulators of
synaptic transmission, we screened the entire
genome of C. elegans for suppressors of
unc-64(e246), a hypomorphic syntaxin allele
that greatly depresses synaptic function. Among
10 suppressors examined, six were alleles of the
Ca 2+ -activated K + channel (SLO-1), notably,
the only K + channel gene identified. unc-64
animals were lethargic and resistant to treatment
with the cholinesterase inhibitor aldicarb. slo-1
mutations partially suppressed the lethargy and
aldicarb-resistance of unc-64. Expression of
wild-type SLO-1 in neurons, but not muscle,
reversed the suppression. To investigate the
physiological basis of suppression, we examined
evoked excitatory postsynaptic currents
(EPSCs) and spontaneous miniature
postsynaptic currents (MPSCs) at the
neuromuscular junction under voltage-clamp
(-60 mV) conditions. The EPSC was induced by
stimulating the ventral nerve cord with a 0.5-ms
DC pulse. Evoked EPSCs at the unc-64
neuromuscular junction were small, with an
amplitude of ~15% and quantal content of ~5%
of wild-type. Addition of a slo-1 mutation
prolonged EPSC duration, resulting in a 4-fold
increase in quantal content. slo-1 mutations also
prolonged EPSCs and increased their
amplitudes in the absence of unc-64. In contrast,
MPSC frequency and amplitude were not
altered by slo-1 mutations, suggesting that the
effects of the mutations were presynaptic. These
results suggest that BK channels plays a key
role in synaptic transmission, possibly by
terminating Ca 2+ influx into the presynaptic
nerve terminal.
49. Electrophysiological
measurement of the action of phorbol
esters and serotonin on body wall
neuromuscular physiology.
Jon Madison, Joshua Kaplan
361 LSA, Dept. of Mol. and Cell Biology,
University of California, Berkeley, CA 94720
We are interested in understanding how
endogenous neuromodulators regulate synapse
function and behavioral responses. In C.
elegans, 5-HT and diacylglycerol (DAG)
modulate the rate of locomotion. Recent genetic
and pharmacological analysis has shown that
5-HT and DAG, or phorbol esters, act
presynaptically on motor neurons to control
acetylcholine (ACh) release at body wall
neuromuscular junctions (NMJs) [1,2]. 5-HT
acts through a G-protein Galphao subunit,
GOA-1, to reduce ACh release at body wall
neuromuscular junctions (NMJs) [1]. In
contrast, DAG or phorbol esters act through
presynaptic phorbol ester receptors, such as
UNC-13, to potentiate ACh release [2]. To
further understand the mechanisms that underlie
these changes in synaptic function, we have
carried out whole cell voltage clamp recordings
from body wall muscle and have recorded the
pre-and post-synaptic effects of 5-HT and
phorbol esters on adult body wall NMJ
physiology.
We have recorded from body wall muscle both
excitatory post-synaptic currents (EPSCs) and
muscle responses to ACh application in the
presence of 5-HT and phorbol esters. At
concentrations of 5-HT greater than 50 microM
the amplitude of ACh-activated currents and
EPSC amplitudes are both reduced by 40% in
the presence of 5-HT, suggesting that 5-HT
regulates the activity of muscle ACh receptors.
By contrast, 25 microM 5-HT does not alter
muscle responsiveness to ACh; however, this
concentration of 5-HT now significantly
reduced the rate of EPSCs. In addition, we have
also analyzed the action of phorbol esters on
synaptic transmission at body wall NMJs. At
concentrations of 10 nM or greater we observe a
2-3 fold increase in the rate of EPSCs while no
post-synaptic changes in ACh activated currents
are observed. We have analyzed putative targets
of phorbol ester potentiation of synaptic
transmission. The protein kinase C mutant,
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