Ascaris suum: regulation of myosin light chain phosphorylation from adult skeletal muscle.

The regulatory myosin light chain in Ascaris suum muscle was isolated in a phospho and dephosphoform. In freshly dissected tissue or in control muscle segments perfused with saline, approximately 48% of the total myosin light chain pool was phosphorylated. Perfusion with acetylcholine caused a dose dependent increase in muscle contraction but no change in myosin light chain phosphorylation. In contrast, perfusion with gamma-aminobutyric acid resulted in a dose dependent relaxation of A. suum muscle and a decrease in myosin light chain phosphorylation so that only 18% of the total myosin light chain remained phosphorylated. Trifluoroperizine, an inhibitor of myosin light chain phosphorylation, did not inhibit acetylcholine induced muscle contraction. Collectively, the data support the hypothesis that A. suum muscle contraction is mediated by actin.