Fig. 5. CCA-1 activity is crucial for the efficient initiation of action potentials in animals with defects in cholinergic neurotransmission. (A) EPGs from unc-17(e245); cca-1(ad1650) double mutants contain many I-phase spikes, reflecting the fact that MC is often unsuccessful in triggering a pharyngeal muscle action potential. The frequency of I-phase spikes is far greater in an unc-17(e245); cca-1(ad1650) double mutant than in an unc-17(e245) single mutant (shown in Fig. 3D). (B) EPGs from snt-1(md290); cca-1(ad1650) mutant worms contain rare action potentials separated by many clusters of I-phase spikes. Again, the rate of failure of action potential generation is far greater in a snt-1(md290); cca-1(ad1650) double mutant than in a snt-1(md290) single mutant (shown in Fig. 3D). EPSPs are marked with large arrows. E-phase spikes are marked with small arrows. I-phase spikes are marked with arrowheads.