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H D Clarke

Publications and source records attributed to H D Clarke.

5 recordsLinked to original sources
PubMed1992

Myofilament lengths of cat skeletal muscle: theoretical considerations and functional implications.

The cat is the primary model for neuromuscular research. However, sarcomere geometry, in particular thin-myofilament lengths of cat skeletal muscles, is not known, thus preventing adequate muscle modeling on the sarcomere level. The purpose of this study was to determine thin-myofilament lengths in cat skeletal muscle. It was found that average thin-myofilament lengths of cat tibialis anterior muscles (1.12 microns) were larger than the average values reported for frog (approximately 0.95 microns), rat (1.09 microns), and rabbit muscles (1.09 microns) and were smaller than the values reported for monkey (1.16 microns) and human skeletal muscles (1.27 microns). According to the cross-bridge theory of muscular contraction, this result implies that the range of sarcomere length on the ascending limb of the force-length relation for cat muscle is between those of frog, rat, and rabbit on the one side and monkey and human on the other side. It is speculated that the differences in thin-myofilament lengths of different animals are related to the functional demands of these muscles in everyday movement tasks. Isolated experimental observations appear to support this speculation.

Actin Cytoskeleton↗
PubMedDate not supplied

The effect of daunomycin on platelets in vitro.

Daunomycin (rubidomycin, daunorubicin), an anthracycline antimetabolite used in the therapy of acute leukemia, is highly toxic to both normal and malignant cells. Treatment with daunomycin may produce thrombocytopenia and bleeding which have been attributed to bone marrow toxicity. We have examined daunomycin to determine if a direct drug effect on platelet structure and function could contribute to a hemorrhagic diathesis in some patients on therapy. Normal citrated platelet-rich plasma was reacted in vitro with daunomycin and/or collagen with structural assessment by phase and electron microscopy and functional studies by platelet aggregation, [2-14C]5-hydroxytryptamine release studies and assays for released cytoplasmic marker enzyme, lactic dehydrogenase, in the supernatant fluid. High [greater than 0.04 mg/ml (greater than 0.07 mM)] concentrations of daunomycin were associated with structural changes, specifically by platelet swelling, vacuole formation and mitochondrial swelling with interruption of the trilaminar membrane. Platelets, exposed to low doses of daunomycin, 0.001 to 0.01 mg/ml (0.00177-0.0177 mM) of platelet-rich plasma, were dysfunctional with decreased aggregation with collagen and decreased [2-14C]5-hydroxytryptamine release. These studies indicate that daunomycin has a direct effect on platelets in vitro which may explain certain instances of bleeding observed in some patients undergoing therapy.

5-Hydroxytryptophan↗