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First published online May 24, 2005
Journal of Experimental Biology 208, 2177-2190 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01615

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CCA-1, EGL-19 and EXP-2 currents shape action potentials in the Caenorhabditis elegans pharynx

Boris Shtonda^* and Leon Avery

Department of Molecular Biology, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75390-9148, USA

^* Author for correspondence (e-mail: boris{at}eatworms.swmed.edu)

Accepted 19 February 2005

The pharynx of Caenorhabditis elegans is a tubular muscle controlled by its own set of neurons. We developed a technique to voltage clamp the pharyngeal muscle and demonstrate by analyzing mutants that the pharyngeal action potential is regulated by three major voltage-gated currents, conducted by a T-type calcium channel CCA-1, an L-type calcium channel EGL-19 and a potassium channel EXP-2.

We show that CCA-1 exhibits T-type calcium channel properties: activation at -40 mV and rapid inactivation. Our results suggest that CCA-1's role is to accelerate the action potential upstroke in the pharyngeal muscle in response to excitatory inputs. Similarly to other L-type channels, EGL-19 activates at high voltages and inactivates slowly; thus it may maintain the plateau phase of the action potential. EXP-2 is a potassium channel of the kV family that shows inward rectifier properties when expressed in Xenopus laevis oocytes. We show that endogenous EXP-2 is not a true inward rectifier - it conducts large outward currents at potentials up to +20 mV and is therefore well suited to trigger rapid repolarization at the end of the action potential plateau phase. Our results suggest that EXP-2 is a potassium channel with unusual properties that uses a hyperpolarization threshold to activate a regenerative hyperpolarizing current.

Key words: calcium channel, L-type/T-type/potassium channel, Caenorhabditis elegans

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