Phyllis E. Hoar

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Of the proteins in mechanically disrupted chicken gizzard fibers (no functional sarcolemma) only the 20,000-dalton light chains of myosin underwent large Ca2+-and Sr2+-dependent changes in phosphorylation. Phosphorylation closely corresponded with the Ca2+- and Sr2+-activated tensions. Adenosine 5'-O (3'-thiotriphosphate) only in the presence of Ca2+(More)
Two isoforms of troponin C (BTnC1 and BTnC2) from the striated muscle of the arthropodBalanus nubilus Darwin (giant barnacle) have been purified (Potteret al., 1987; Collinset al., 1991). Both isoforms were present in all of the white striated muscle fibres studied but not in the red fibres. The ratio of BTnC2 to BTnC1 in different fibre types varied(More)
beta-Adrenergic relaxation of smooth muscle by catecholamines has been associated with elevated levels of cyclic AMP. The question arises whether subsequent activation of cyclic AMP-dependent protein kinase has a role in the regulation of smooth muscle contraction. There is substantial evidence that a Ca2+-activated myosin light chain kinase/phosphatase(More)
The mechanism of contraction in rabbit fast-twitch, and bovine and rabbit cardiac muscle was examined using functionally skinned fibers, ATPase activity of myofibrils, and cardiac or skeletal troponintropomyosin regulated actin heavy meromyosin. The Ca2+ and Sr2+ activation properties for the different measures of contraction were evaluated. (1) Tension in(More)
The role of protein kinase C (PKC) in regulating the contractile state of smooth muscle was investigated using the constitutively active catalytic fragment of PKC (PKM) with skinned (demembranated) chicken gizzard fibres. PKM attenuated a submaximal contraction in gizzard smooth muscle skinned fibres, but not in rabbit cardiac skinned fibres. PKM-mediated(More)
Isometric force developed by skinned gizzard muscle fiber bundles and levels of phosphorylation and thiophosphorylation of the 20,000-dalton myosin light chain were determined. These data showed a highly non-linear relationship between isometric force and myosin light-chain phosphorylation. Maximum force was developed at approximately 0.2 mol of(More)
Increasing concentrations of MgADP− or MgCDP− in the millimolar range cause an increase in the maximum Ca2+-activated tension that a skinned rabbit soleus muscle fiber can develop in the presence of 2 mM MgATP2− or MgCTP2 respectively. In contrast, the maximal Ca2+-activated ATPase activity of the fiber decreases in the presence of MgADP−. As the nucleoside(More)
We have investigated the effect of exogenous calmodulin on chicken gizzard or rabbit ileum smooth muscle functionally skinned by mechanical grinding or exposure to Triton X-100 detergent. We found that a specific protein inhibitor, modulator binding protein, caused a loss of Ca2+-activated tension which was restored by subsequent treatment with calmodulin.(More)
The primary purpose of this study was to determine whether various agents (adenosine 3-thiotriphosphate [ATP gamma S], trifluoperazine [TFP], troponin I, the catalytic subunit of the cyclic adenosine 3',5'-monophosphate dependent protein kinase [C-subunit], and calmodulin [CaM]) could be used to classify skinned fiber types, and then to determine whether(More)
Rabbit ileum strips were functionally skinned by exposure to staphylococcal alpha-toxin. Incubation of the strips in the ATP analog ATP gamma S or [35S]ATP gamma S in the presence of Ca2+ (but not in the absence of Ca2+) resulted in a maximal Ca2+-insensitive activated tension that persisted following removal of Ca2+. Correlated with this tension was(More)