Calcium-dependent muscle contraction in obliquely striated Ascaris suum muscle

The regulatory proteins of Ascaris suum striated skeletal muscle were partially purified and characterized. A tropomyosin isoform (Mr 41K) and three troponin subunits identified as troponin T (Mr 37.5K), troponin I (Mr 25.5K) and troponin C (Mr 18.5K) were purified. Three myosin light chains (Mr 25K, 19K, and 17K) were isolated from washed Ascaris actomyosin; the 19K subunit was phosphorylated in vitro. A calcium/calmodulin-dependent myosin light chain kinase activity was identified in the muscle. In contrast to previously reported data suggesting that Ascaris obliquely striated muscle contraction is regulated by a myosin-mediated mechanism, these data indicate that all of the proteins required for actin-mediated, calcium-dependent muscle contraction are present in this tissue.     

New intragenic deletions in the Phex gene clarify X-linked hypophosphatemia-related abnormalities in mice

X-linked hypophosphatemic rickets (XLH) in humans is caused by mutations in the PHEX gene. Previously, three mutations in the mouse Phex gene have been reported: Phex^Hyp, Gy, and Phex^Ska1. Here we report analysis of two new spontaneous mutations in the mouse Phex gene, Phex^Hyp-2J and Phex^Hyp-Duk. Phex^Hyp-2J and Phex^Hyp-Duk involve intragenic deletions of at least 7.3 kb containing exon 15, and 30 kb containing exons 13 and 14, respectively. Both mutations cause similar phenotypes in males, including shortened hind legs and tail, a shortened square trunk, hypophosphatemia, hypocalcemia, and rachitic bone disease. In addition, mice carrying the Phex^Hyp-Duk mutation exhibit background-dependent variable expression of deafness, circling behavior, and cranial dysmorphology, demonstrating the influence of modifying genes on Phex-related phenotypes. Cochlear cross-sections from Phex^Hyp-2J/Y and Phex^Hyp-Duk/Y males reveal a thickening of the temporal bone surrounding the cochlea with the presence of a precipitate in the scala tympani. Evidence of the degeneration of the organ of Corti and spiral ganglion also are present in the hearing-impaired Phex^Hyp-Duk/Y mice, but not in the normal-hearing Phex^Hyp-2J/Y mice. Analysis of the phenotypes noted in Phex^Hyp-Duk/Y an Phex^Hyp-2J/Y males, together with those noted in Phex^Ska1/Y and Phex^Hyp/Y males, now allow XLH-related phenotypes to be separated from non-XLH-related phenotypes, such as those noted in Gy/Y males. Also, identification of the genetic modifiers of hearing and craniofacial dysmorphology in Phex^Hyp-Duk/Y mice could provide insight into the phenotypic variation of XLH in humans. *Bothauthorscontributedequallytothisresearch.     

Correlation of myosin light chain phosphorylation and gamma aminobutyric acid receptors in Ascaris suum muscle

Four different muscle relaxants were compared as to their effects on tonic Ascaris suum muscle to: physiological activity, intracellular response to regulatory light chain phosphorylation, and receptor pharmacology. Perfusion of Ascaris suum muscle with each relaxant, gamma-aminobutyric acid, avermectin, piperazine and chlorpromazine resulted in a dose-dependent loss of muscle tone. Comparison of intracellular effects indicated that gamma-aminobutyric acid and avermectin perfusion initiated an increase in the levels of dephosphorylated regulatory light chain while piperazine increased first site phosphorylation and chlorpromazine increased second site phosphorylation. Receptor pharmacology studies were used to compare the actions of gamma-aminobutyric acid and piperazine. It was found that bicuculline-methiodide and picrotoxin inhibited the effects of gamma-aminobutyric acid in a dose-dependent manner, but these drugs had no effect on muscle relaxation stimulated with piperazine.