PubMed Health⌕ Search

Biomedical subjects

R Nesher

Publications and source records attributed to R Nesher.

60 records · Page 4Linked to original sources
PubMed1980

Epitrochlearis muscle. I. Mechanical performance, energetics, and fiber composition.

An in vitro rat muscle preparation is described that can contract at rates of 12-240 twitches/min. Maximum dF/dt paralleled maximum twitch tension, their ratio being constant at approximately 8 ms for contraction rates of 12-120 twitches/min. Time to peak tension was 8-13 ms, time to peak dF/dt 5-8 ms, and half-relaxation time 4 ms. These parameters were unaffected by rate of contraction or duration of isometric work. Differential ATPase staining demonstrated that 60-65% of the fibers were fast-twitch white, 20% fast-twitch red, and 15% slow-twitch red. The preponderance of fast-twitch fibers correlated with the observed mechanical performance of the muscle. Muscles contracting for 60 min at rates up to 48 twitches/min maintained total adenine nucleotide content (ATP, ADP, AMP) at near resting levels. At higher twitch rates (72-240 twitches/min), total adenine nucleotide content decreased 40%, reflecting exclusively a fall in ATP in the presence of adequate phosphocreatine stores. Adequate oxygenation was reflected by lactate-to-pyruvate ratios in the range of 11-15 at all rates of contraction.

Adenosine Triphosphatases↗
PubMed1980

Epitrochlearis muscle. II. Metabolic effects of contraction and catecholamines.

Effects of isometric contraction and catecholamines on glucose and glycogen metabolism in skeletal muscle were investigated with the in vitro rat epitrochlearis preparation. Mechanical performance and glycogenolysis exhibited two phases. During the initial 30 min, muscle work was 30% greater and glycogenolysis 8- to 10-fold faster than the steady-state values in the subsequent 3-4 h of contraction. Glucose uptake was increased by contraction and remained relatively constant during stimulation. Epinephrine (10(-9) to 10(-6) M) and norepinephrine (10(-7) to 10(-5) M) produced inotropic and glycogenolytic effects blocked by propranolol but not phentolamine. Chemical sympathectomy and propranolol blocked the initial glycogenolytic and inotropic effects produced by isometric contraction, suggesting that they were caused by the release of endogenous catecholamines. Net lactate production in resting muscles accounted for > 50% of total glucosyl units utilized. During contraction net lactate production accounted < 10-15% of total glycosyl flux indicating that rat fast-twitch pale muscle is capable of significant rates of aerobic glucose oxidation. Oleate and caprylate did not affect mechanical performance, glycogen, or glucose metabolism in resting or contracting muscles.

Animals↗
PubMed1977

Cyclic nucleotide levels in the perfused rat heart subjected to hypoxia.

Isolated rat hearts were subjected to hypoxic perfusion on a recirculating Langendorff apparatus. Following a 30-min-period of aerobic stabilization the hearts were perfused for 30 min with media equilibrated with 84% N2, 12%O2 and 4% CO2. At the end of the hypoxic period myocardial concentrations of cyclic AMP and cyclic GMP were determined by radioimmunoassay. Exposure to hypoxia resulted in a significant increase in cyclic AMP (p less than 0.01) and a decrease in cyclic GMP (p less than 0.05) as compared to hearts perfused for 60 min with media gassed with 96% O2. 4% CO2.

Animals↗
PubMedDate not supplied

The methodology for studying coordinated calcium concentration changes in a pancreatic beta cell line.

Intracellular calcium concentration was imaged in beta Tc cells with the aid of Fluo-3 indicator and the Meridian ACAS 570 interactive laser cytometry. This cell line does not respond by an elevation in [Ca2+]in to increase in extracellular [glucose], but does respond to 10 microM forskolin. It was found that forskolin increases the mean [Ca2+]in and produces calcium spikes. Time series analysis was performed on individual pixels. Autocorrelation revealed that forskolin induces oscillation in [Ca2+]in. Cross-correlation analysis showed that all the intracellular pixels along the line scan are highly correlated, indicating that the increase in [Ca2+]in encompasses the entire cell.

Aniline Compounds↗