C. elegans feeds by stereotypic contraction and relaxation of pharygeal muscles. Contraction is dictated by muscle electrical activity, which can be monitored by electropharyngeograms (Raizen and Avery, Neuron 12: 483). To understand feeding behavior, we have isolated and characterized mutants that affect the pharyngeal muscle action potential.
eat-12 is an important regulator of muscle excitation, not just in the pharynx but probably in all muscles. Gain-of-function mutations in
eat-12 (one was kindly provided by Michael Hengartner and Bob Horvitz) prolong pharyngeal muscle action potentials and thus cause hypercontraction. The mutants are short and egg-laying constitutive. In contrast, partial loss-of-function mutants of
eat-12 show feeble muscle contraction. Mutants are long, loopy and egg-laying defective. Preliminary evidence indicates that in these mutants pharyngeal muscle action potentials have a reduced rate of depolarization.
eat-12 probably affects muscle excitation directly since null mutants arrest at the two-fold stage (Pat phenotype). Normally, embryonic muscle contraction occurs apparently independently of the nervous system function at this stage. To further characterize
eat-12 genetically, we isolated 20 new alleles either by reverting the dominant alleles or by non-complementation of the recessive alleles. We found that
eat-12 is the same locus as the previously identified genes
egl-19 (Trent et al., Genetics 104: 619) and
pat-5 (Williams and Waterston, JCB 124: 475). We also isolated intragenic suppressors of
egl-19(
n582), one of which reverts
n582 to nearly wild-type phenotype. We are collaborating with Leslie Lobel to clone
eat-12. Preliminary evidence suggests that
eat-12 encodes a worm homolog of the alpha1-subunit of the mammalian L-type voltage-gated calcium channel. Leslie Lobel cloned a partial cDNA of a calcium channel gene by PCR and mapped it onto YACs close to
eat-12 (Lobel et al., WBG 13.1: 46). We localized it to a cosmid and showed that the cosmid can rescue several
eat-12 mutants by germ line transformation. We are analyzing
eat-12 alleles to see if the calcium channel gene is mutated. Together, these observations suggest that
eat-12, as a voltage-gated calcium channel, is a crucial component in generating muscle action potentials. It hastens depolarization and regulates the duration of an action potential. Our extensive collection of
eat-12 mutants may facilitate structure-function analysis of calcium channels.