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Biomedical subjects

R Zak

Publications and source records attributed to R Zak.

At least 127 records · Page 7Linked to original sources
PubMed1977

Studies of isolated adult rat heart cells: the surface morphology and the influence of extracellular calcium ion concentration on cellular viability.

Rat cardiac muscle was dissociated into single cells by a coronary perfusion technique with collagenase and hyaluronidase in a Ca-free medium. Retention of the cylindrical shape of isolated muscle cells could be achieved by regulation of [Ca2+]0 and temperature. Cells kept at 4 degrees C, and 0-01 mM CaCl2 remained cylindrical for more than a week and contracted spontaneously upon warming at 37 degrees C. At [Ca2+]0 between 0-1-2 mM and 37 degrees C, cells underwent contracture and rounded up. Scanning (SEM) and transmission electron microscopy were used to analyze the structure of cylindrical and rounded muscle cells. The extracellular aspect of the sarcolemma at lateral cell surfaces and intercalated disc regions were clearly revealed for SEM analysis. Both the distribution and number of T-tubule openings on the surfaces can be estimated and a three-dimensional description of the intercalated disc obtained. This study reveals that isolated adult heart cells are extremely sensitive to [Ca2+]0, but with careful control of this cation, this preparation should be helpful in the analysis of both sarcolemmal structure and the pathological changes which accompany myocardial injury.

Animals↗
PubMed1976

Compositional studies of myofibrils from rabbit striated muscle.

The localization of high-molecular-weight (80,000-200,000-daltons) proteins in the sarcomere of striated muscle has been studied by coordinated electron-microscopic and sodium dodecyl sulfate (SDS) gel electrophoretic analysis of native myofilaments and extracted and digested myofibrils. Methods were developed for the isolation of thick and thin filaments and of uncontracted myofibrils which are devoid of endoproteases and membrane fragments. Treatment of crude myofibrils with 0.5% Triton X-100 results in the release of a 110,000-dalton component without affecting the myofibrillar structure. Extraction of uncontracted myofibrils with a relaxing solution of high ionic strength results in the complete disappearance of the A band and M line. In this extract, five other protein bands in addition to myosin are resolved on SDS gels: bands M 1 (190,000 daltons) and M 2 (170,000 daltons), which are suggested to be components of the M line; M 3 (150,000 daltons), a degradation product; and a doublet M 4, M 5 (140,000 daltons), thick-filament protein having the same mobility as C protein. Extraction of myofibrils with 0.15% deoxycholate, previously shown to remove Z-line density, releases a doublet Z 1, Z 2 (90,000 daltons) with the same mobility as alpha-actinin, as well as proteins of 60,000 daltons and less, and small amounts of M 1, M 2, M 4, and M 5; these proteins were not extracted with 0.5% Triton X-100. The C, M-line, and Z-line proteins and/or their binding to myofibrils are very sensitive to tryptic digestion, whereas the M 3 (150,000 daltons) component and an additional band at 110,000 daltons are products of proteolysis. Gentle treatment of myofibrils with an ATP relaxing solution results in the release of thick and thin myofilaments which can be pelleted by 100,000-g centrifugation. These myofilaments lack M-and Z-line structure when examined with the electron microscope, and their electrophoretograms are devoid of the M 1, M 2, Z 1, and Z 2 bands. The M 4, M 5 (C-protein doublet), and M 3 bands, however, remain associated with the filaments.

Animals↗
PubMed1976

Control of protein balance in hypertrophied cardiac muscle.

The levels of intracellular proteins are determined by a balance between their rates of synthesis and degradation. During the development of regression of cardiac hypertrophy, both of these rates can be expected to change. Possible control sites of synthetic and degradation processes are discussed in this article. The following experimental results are presented: (1) Cardiac mitochondrial cytochromes accumulate early after imposition of pressure overload, as a result of an increased rate of synthesis and decreased rate of degradation. (2) The half-life of myosin heavy chains (HC) in the steady state was determined from incorporation kinetics, using leucyl-tRNA as precursor, to be 5-6 days. (3) The existence of a pool of newly synthesized myofilaments which are not fully incorporated into the core of myofibrils is indicated by the incorporation data.

Animals↗
PubMed1975

Removal of Z-lines and alpha-actinin from isolated myofibrils by a calcium-activated neutral protease.

A calcium-activated factor (CaAF) has been isolated and partially purified from the post-myofibrillar supernatant fraction of rabbit skeletal muscle. The 200-fold purified CaAF hydrolyzed denatured casein, [3-H]acetyl hemoglobin, and N-ethyl[3-H]maleimide-labeled alpha-actinin. The proteolytic activity has a pH optimum at 6.9 and is dependent on the presence of Ca2+ (optimum concentration, 10 mM). Digestion of isolated myofibrils with CaAF results in removal of Z-lines and in a parallel loss of a 90, 000-dalton protein that has a mobility identical with that of alpha-actinin as determined by polyacrylamide gel electrophoresis. A protein with the properties of alpha-actinin (identical electrophoretic mobility, and ability to accelerate the Mg2+-activated ATPase of reconstituted actomyosin) was isolated from the supernatant of CaAF-treated myofibrils. The release of alpha-actinin from myofibrils by the calcium-activated neutral protease occurs in the absence of detectable change in the electrophoretic profiles of the other myofibrillar proteins, or in the ethylene glycol bis(beta-aminoethyl ether)-N, N' tetraacetic acid (EGTA) sensitivity of Mg2+-activated ATPase. In contrast to the specific removal of Z-lines and of alpha-actinin by CaAF, trypsin treatment of myofibrils results in extensive degradation of myosin heavy chains and of the inhibitory component of troponin (TN-I), and in loss of EGTA sensitivity of myofibrillar ATPase. The degradation of TN-I and loss of EGTA sensitivity occur before the Z-line disappearance.

Animals↗
PubMed1975

Lysosomal and neutral hydrolase activity during the regression of cardiac hypertrophy.

Cardiac hypertrophy was produced in rats by constriction of the ascending aorta. Removal of the constricting band 10 days after operation resulted in rapid decline in left ventricular (LV) weight and total ventricular RNA. Activities of acid RNase and beta-glucuronidase were elevated 3 days after aortic constriction. Activities of cathepsin D and alkaline RNase were unchanges. Activities of cathepsin D and acid RNase were unchanged 1 and 3 days after removal of constricting band. Ca2+-activated, neutral protease (CAF) isolated from postmitochondrial muscle supernatant was partially purified and characterized. CAF specifically degrades alpha-actinin when incubated with isolated myofibriles in the presence of Ca2+.

Animals↗