Studies into the functional properties of the Pharyngeal Muscle of Caenorhavditis Elegans

Caenorhabditis elegans is a well described nematode employed as a genetic model organism for studies into function, differentiation, development, and morphology of simple nervous and muscular systems. However, essential information regarding its physiology and pharmacology are lacking. To address this, electrophysiological recording techniques from pharyngeal muscle cells were developed to determine the ionic basis of the resting membrane potential and action potential. Resting membrane potential of pharyngeal muscle cells were relatively unaffected by changes in the extracellular concentrations of Cl-, Na+ or Ca++. However, variations in extracellular concentrations of K+, or exposure to ouabain, both elicited a depolarisation, although the depolarisations observed during elevations of extracellular K+ were less than would be predicted if the membrane potential were completely dependent on K+. It can be concluded therefore, that the resting membrane potential is largely determined by a K+ permeability, and a ouabain-sensitive, electrogenic pump. Action potential height was reduced or increased in concentration-dependent manner following exposure to low or high extracellular Ca++ concentrations respectively. Furthermore, the L-type Ca++ channel blockers, verapamil and nifedipine, both reduced action potential amplitude and duration. This suggests a role for an L-type Ca++ channel in the action potential. However, action potentials persisted in Ca++ free saline. Action potential duration increased or decreased in a concentration-dependent manner following exposure to low or high Ca++ concentrations respectively. This suggests that the repolarisation phase is partly determined by a Ca++ activated K+ channel. Possibly the most surprising finding was the absolute dependence of pharyngeal action potential generation on extracellular Na+ concentration, especially as extensive searches of the C. elegans genome have failed to find any obvious candidate for a voltage-gated Na+ channel.</p