The pharynx of C. elegans is a rhythmically active muscle that pumps bacteria into the gut of the nematode. This activity is maintained by action potentials, which qualitatively bear a resemblance to vertebrate cardiac action potentials. Here, the ionic basis of the resting membrane potential and pharyngeal action potential has been characterized using intracellular recording techniques. The resting membrane potential is largely determined by a K(+) permeability, and a ouabain-sensitive, electrogenic pump. As previously suggested, the action potential is at least partly dependent on voltage-gated Ca(2+) channels, as the amplitude was increased as extracellular Ca(2+) was increased, and decreased by L-type Ca(2+) channel blockers verapamil and nifedipine. Barium caused a marked prolongation of action potential duration, suggesting that a calcium-activated K(+) current may contribute to repolarization. Most notably, however, we found that action potentials were abolished in the absence of external Na(+). This may be due, at least in part, to a Na(+)-dependent pacemaker potential. In addition, the persistence of action potentials in nominally free Ca(2+), the inhibition by Na(+) channel blockers procaine and quinidine, and the increase in action potential frequency caused by veratridine, a toxin that alters activation of voltage-gated Na(+) channels, point to the involvement of a voltage-gated Na(+) current. Voltage-clamp analysis is required for detailed characterization of this current, and this is in progress. Nonetheless, these observations are quite surprising in view of the lack of any obvious candidate genes for voltage-gated Na(+) channels in the C. elegans genome. It would therefore be informative to re-evaluate the data from these homology searches, with the aim of identifying the gene(s) conferring this Na(+), quinidine, and veratridine sensitivity to the pharynx.

The pharynx of Caenorhabditis elegans consists of a syncytium of radially orientated muscle cells that contract synchronously and rhythmically to ingest and crush bacteria and pump them into the intestine of the animal. The action potentials that support this activity are superficially similar to vertebrate cardiac action potentials in appearance with a long, calcium-dependent plateau phase. Although the pharyngeal muscle can generate action potentials in the absence of external calcium ions, action potentials are absent when sodium is removed from the extracellullar solution (Franks et al. 2002). Here we have used whole cell patch clamp recordings from the pharynx and show low voltage-activated inward currents that are present in zero external calcium and reduced in zero external sodium ions. Whilst the lack of effect of zero calcium when sodium ions are present is not surprising in view of the known permeability of voltage-gated calcium channels to sodium ions, the reduction in current in zero sodium when calcium ions are present is harder to explain in terms of a conventional voltage-gated calcium channel. Inward currents were also recorded from egl-19 (n582) which has a loss of function mutation in the pharyngeal L-type calcium channel and these were also markedly reduced in zero external sodium. Despite this apparent dependence on external sodium ions, the current was partially blocked by the divalent cations, cadmium, barium and nickel. Using single-channel recordings we identified a cation channel for which the open-time duration was increased by depolarisation. In inside-out patches, the single-channel conductance was highest in symmetrical sodium solution. Further studies are required to determine the contribution of these channels to the pharyngeal action potential.

In experienced hands thoracic surgery yields excellent results for children suffering from pleural empyema stage II and III. Recent randomised prospective trials comparing fibrinolysis with VATS do not convince regarding the treatment protocols of their surgical arms. Fibrinolysis is nevertheless a valuable treatment in early stage II empyema, especially if thoracic surgical experience is not available. However, the further advanced the empyema presents, the sooner surgical experience should be gathered.

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