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The high stiffness of relaxed cardiac myofibrils is explainable mainly by the expression of a short-length titin (connectin), the giant elastic protein of the vertebrate myofibrillar cytoskeleton. However, additional molecular features could account for this high stiffness, such as interaction between titin and actin, which has previously been reported in(More)
The role of orthophosphate ions (Pi) in crossbridge kinetics was investigated by parallel measurements of the ATP hydrolysis rate and tension transients in maximally activated, chemically skinned rabbit psoas fibers. The hydrolysis rate of the standard activation at 20 degrees C was measured at 1.25 nmole X s-1 X m-1 X fiber-1, which corresponds to the(More)
Smooth muscle contraction depends on the state of myosin phosphorylation and hence on the balance of myosin light chain kinase and phosphatase activity. Effects of okadaic acid isolated from black sponge on both enzyme activities and contractility were studied in chemically skinned fibers from guinea pig taenia coli. The toxin strongly inhibits myosin(More)
Vertebrate striated muscle behaves elastically when stretched and this property is thought to reside primarily within the giant filamentous protein, titin (connectin). The elastic portion of titin comprises two distinct structural motifs, immunoglobulin (Ig) domains and the PEVK titin, which is a novel motif family rich in proline, glutamate, valine and(More)
1. Twitch fibres isolated from the sartorius muscle of the frog were glycerinated (cf. Heinl, 1972) and thin fibre bundles dissected from the m. ileofibularis of the tortoise were briefly glycerinated as described by Julian (1971).2. The glycerinated fibres (length 0.3-0.5 cm) were fixed to an apparatus which performed length changes within 5 msec and(More)
The effects of a protein phosphatase inhibitor, okadaic acid (OA), were studied on membrane currents of isolated myocytes from guinea-pig cardiac ventricle. The whole-cell Ca2+ current (ICa) was recorded as peak inward current in response to test pulse to 0 mV. Extracellular application of OA (5-100 microM) produced an increase of ICa. The effect was(More)
Different myosin isoenzymes of pig and human atrium and ventricle and rat ventricle were characterized by two approaches: pyrophosphate polyacrylamide gel electrophoresis (PP-PAGE) and analysis of the myosin P light chains by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). We further investigated the relation between atrial and ventricular(More)
A new technique for treating skinned cardiac muscle fibers has been developed in which troponin I is extracted, giving rise to unregulated fibers. The effect of the 12-residue troponin I peptide on these fibers indicates that this region of troponin I is solely responsible for muscle relaxation (inhibition of force). Furthermore, troponin I peptide-troponin(More)
Recent work on vascular smooth muscle actomyosin has indicated that the Ca2+ sensitivity of both ATPase and superprecipitation are affected by calmodulin (CaM) and cyclic AMP-dependent protein kinase (cPK). Using a "chemically skinned" arterial preparation, we have extended these observations to the intact structured contractile system. Media from hog(More)