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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



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  		Fig. 1. The pharynx skinning procedure. (A) Schematic of the C. elegans pharynx as it is positioned in the worm's head. To dissect the pharynx, the head is cut off between the pharynx and the intestine. Three compartments of the pharynx are shown. Area of patch pipette attachment (shaded area of the corpus) roughly corresponds to the pm4 muscle cell of the pharynx. (B) Cut-off worm's head. (C) Body wall inversion using two pipettes. The smaller pipette (left) is pushed into the bigger one, inverting the body wall. (D) Skinned and digested pharynx, before patching. TB, terminal bulb.

 


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  		Fig. 2. Depolarization-activated inward currents in the pharynx. (A) Total inward currents in the wild type (WT) and in the cca-1 mutant. (B) High voltage-activated (HVA) currents in the WT and in cca-1. In these experiments the low voltage-activated (LVA) current was inactivated with a 300 ms prepulse to -40 mV. (C) Ni2+ (2 mmol l-1) blocks both the LVA and the HVA currents. (D) Nifedipine (10 µmol l-1) blocks the HVA, but not the LVA current. Recordings in C and D are from wild-type pharynxes, and the pulse protocol is the same as in A. Numbers next to current traces indicate peak depolarization of the voltage pulse.

 


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  		Fig. 3. Current-voltage (I-V) relationships for inward currents in the wild-type and cca-1 pharynxes. (A) Wild type. (B) cca-1.. Voltage protocols for the total current and current in the presence of 10 µmol l-1 nifedipine were the same as in Fig. 2A: depolarizing pulses were applied in 10 mV increments starting from the holding potential of -80 mV. HVA currents were measured with the same voltage protocol as in Fig. 2B: LVA current was inactivated with the prepulse to -40 mV. For nifedipine experiments, averaged current values at 50-60 ms of the pulse were used (after the LVA current has inactivated); otherwise, peak amplitudes were used for I-V curves.

 


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  		Fig. 4. The EGL-19 L-type calcium channel conducts the HVA current in the pharynx. (A) Total currents in cca-1 and cca-1; egl-19. 100 ms depolarizing pulses were applied in 10 mV increments from the holding potential of -80 mV (same protocol as in Fig. 2A). (B) HVA currents in wild type and egl-19. The LVA current was inactivated with a 300 ms prepulse to -40 mV (same protocol as in Fig. 2B). (C) Current-voltage dependencies of HVA currents in WT and egl-19 (peak amplitudes; prepulse protocol). (D) Activation time constants of HVA currents in WT and egl-19; *significantly different by t-test, P<0.01.

 


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  		Fig. 5. EXP-2 conducts hyperpolarization-activated outward current. (A) Sample recordings from the WT and exp-2.. (B) Current-voltage (I-V) relationships (peak amplitudes).

 


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  		Fig. 6. The slope of the plateau phase determines the onset of the EXP-2 current. (Top) voltage commands; (bottom) corresponding currents from one pharynx. (A) Outward currents in response to varying voltage ramps starting from the same depolarization to +33 mV. (B) Outward currents in response to varying peak depolarizations followed by the same negative ramp of -0.22 V s-1. On command voltage traces, average timings of EXP-2 current transients are indicated by black diamonds (N=4 pharynxes), and dotted lines show parameters of the wild-type pharynx, as determined by voltage recordings. For clarity, standard deviations for the voltage only are shown in A, and for the timing only are shown in B. All recordings are from wild type.

 


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  		Fig. 7. Model of the pharyngeal action potential. Currents are not drawn to scale. Currents resulting from M3 neurotransmission are omitted for clarity.

 

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© The Company of Biologists Ltd 2005