Worm Breeder's Gazette 13(5): 34 (February 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Intracellular recording from pharyngeal muscles

M. Wayne Davis (wayne@eatworms.swmed.edu) and Leon Avery

Dept. of Biochemistry, University of Texas Southwestern Medical Center
5323 Harry Hines Blvd., Dallas, TX 75235-9038.

     Like the vertebrate heart, the pharynx is a neuromuscular pump that
is active throughout the life of the worm. In order to examine the
electrical events that occur during a pharyngeal pump, the
electropharyngeogram (EPG) - a fast, easy method for measuring electrical
signals generated by the pharyngeal muscles of an intact worm (Neuron
12:483-495)- was developed. This method measures the currents that flow as
a result of voltage changes during a muscle action potential, and so
represents the temporal derivative of the action potential. We have used
intracellular recording to measure the absolute voltage levels across the
muscle membranes during the action potential. This method requires
dissecting the pharynx out of the worm into saline (Joseph Dent WBG 13(1):
44) and then, using a large diameter suction pipette to hold the terminal
bulb, inserting a glass electrode into the muscle. The electrode filled
with 500mM potassium acetate has a resistance around 250Mohms. The trans-
membrane voltage is measured with an Axoclamp 1D amplifier in bridge mode.
A series of three action potentials from a wild-type worm is shown in
figure 1a. These records closely resemble recordings form the pharyngeal
muscle of Ascaris (Del Castillo and Morales (1967). J. Gen. Physiol. 50:
603-629) and are somewhat similar to vertebrate heart action potentials.
A small depolarizing event- possibly an excitatory postsynaptic potential-
precedes these pumps, but is not always seen.  The rising phase of the
action potential is fast and is followed by a longer plateau phase that
ends with a rapid repolarization that overshoots the resting potential.
eat-6 encodes a Na,K-ATPase gene and the EPG from eat-6 worms has a
smaller excitation spike and a very small relaxation spike (WBG 13(2):52).
Recordings from eat-6 mutant worms (figure 1b) show a more positive
resting potential, smaller depolarizations, and slower repolarizations
with less overshoot. Further work using ionic substitution, pharmacology,
and of course mutants will hopefully tell us about the variety of channels
that must be working to cause these events.