Pharyngeal muscles exhibit two distinct types of contractions called pumps and peristalses. A peristalsis is a wave-like contraction followed by rapid relaxation that travels posteriorly through the isthmus, so that only a small portion of the isthmus lumen is open at any time. This contraction is remarkable, because it occurs within individual
pm5 muscle cells that extend the entire length of the pharyngeal isthmus. Peristalses occur only after several pumps, and they are dependent on signals from the M4 motor neuron. We are examining how M4 and the isthmus muscles interact to produce these peristalses. M4 is a cholinergic neuron, and we have found that
cha-1 mutants lacking acetylcholine (ACh) fail to pump or peristalse. Chemical stimulation of either muscarinic or nicotinic ACh receptors (mAChRs and nAChRs) in
cha-1 mutants is sufficient to activate peristalsis. We have examined several mutants affecting AChR genes expressed in the pharyngeal muscles and have found that mutants defective in the nAChR
eat-2 and the mAChR
gar-3 exhibit distinct peristaltic defects.
eat-2 mutants pump and peristalse less frequently than wild-type animals, but the
eat-2 peristalses are prolonged suggesting that EAT-2 inhibits isthmus muscle contraction. In comparison,
gar-3 mutants fail to respond to the mAChR agonist arecoline indicating GAR-3 mediates peristalsis in response to exogenous arecoline. In addition the
gar-3 mutation suppresses the prolonged peristalses observed in
eat-2 mutants, which suggests GAR-3 stimulates peristalsis even in the absence of exogenous arecoline. To understand how these AChRs affect peristalsis, we are examining Ca2+ dynamics in the isthmus muscles using GCaMP3. Wild-type animals display a broad increase in Ca2+ in the center of the isthmus during pumps followed by a wave-like increase in Ca2+ in the posterior isthmus during peristalses. We plan to analyze these dynamic Ca2+ changes in
eat-2 and
gar-3 mutants to understand how these different receptor types contribute to isthmus peristalsis.