Uptake of tritium-labeled norepinephrine in brain and other tissues of cat in vitro

Slices of cat cerebral cortex, heart, and spleen that have been incubated in media containing approximately 5 to 25 mmicrog of dl-norepinephrine-7H(8) per milliliter contain levels of isotopic amine greater than those in the medium. The effects of norepinephrine concentration, reserpine, and ouabain on the uptake suggest that the amine enters cells both by diffusion and by a concentrating miechanism that is saturated at low levels of norepinephrine. The drugs inhibit the latter.

Potassium flux in the isolated perfused rabbit heart

The exchange kinetics of potassium in the isolated, perfused rabbit heart have been studied in relation to changes in heart rate, extracellular potassium and temperature. The intracellular potassium appeared to exist in at least two compartments, the relative size varying with the extracellular concentration of potassium. The change in the potassium flux between heart rates of 100 and 200 beats/min. was compared to a change in flux calculated on the basis of the theory proposed by Hodgkin and co-workers and electrical constants taken from the literature. The change in flux estimated from the experimental curves was somewhat smaller than that required by theory and a discussion of this result is given. The activation energy calculated for the total potassium flux into and from the cells was estimated to be from 3000 to 8000 cal/ mole and found to be a function of the potassium concentration in the perfusate.

Reversible inhibition of beef heart cytochrome c oxidase by polyionic macromolecules

The basic proteins protamine (sulfate), histone, lysozyme, and ribonuclease were found to be potent inhibitors of mammalian heart muscle cytochromec oxidase. Their inhibitions were completely reversed in the presence of a strongly anionic polyglucose sulfate. With fresh rat heart muscle homogenates, Keili and Hartree type of beef heart muscle particulates, and deoxycholate-solubilized oxidase preparations, the reversible nature of the phenomenon was demonstrated with manometric and spectrophotometric assays for cytochrome c oxidase.

A possible correlation between ATPase activity and Na content of embryonic chick heart

The water content of embryonic chick ventricles decreases gradually from 88% at 2 days of incubation to 83% shortly after hatching. Ventricular protein nitrogen decreases during early development and then increases rapidly at midfetal age until hatching, after which a more gradual increase continues. Magnesium-activated ATPase activity of whole ventricle homogenates at pH 7.0–7.5 is much greater than is the calcium-activated enzyme throughout development. A very marked increase in Mg-ATPase occurs between 4 and 7 days of incubation; a lesser increase occurs just prior to and after hatching. Calcium-ATPase increases gradually throughout development. Magnesium-ATPase has been identified with both isolated mitochondrial and microsomal fractions; Ca-ATPase is exclusively associated with the myosin fraction. Myokinase occurs in the supernatant. Optimal pH's are given for the enzymes. It is suggested that the initial rapid fall in ventricular Na content between 2 and 7 days of incubation is directly related to two events: disappearance of the cardiac jelly and establishment of an effective Na extrusion mechanism.

Enzymatic activity in the M band

Experiments which combined histochemistry and electron microscopy were performed in studying the sites of enzymatic hydrolysis of thiolacetic acid in the presence of lead ions in diaphragmatic and cardiac muscle. It was found that in these striated muscles the electron opaque, final product of the histochemical reaction (PbS) was discretely deposited on the swelling of the thick elemental filaments that occurs at the M band. Additional sites of enzymatic activity occurred in mitrochondria and in round sarcoplasmic bodies. A reaction, probably non-enzymatic, also occurred in contraction bands in the area of the Z bands and in the sarcoplasmic reticulum. To ascertain the enzymatic nature of the reaction and to define the enzyme involved, control experiments were carried out and the effect of various esterase inhibitors was assayed. It is suggested that the M band enzyme is a cholinesterase, but the enzymes in the mitochondria and the sarcoplasmic bodies that hydrolyze the substrate appear to be different. A possible role of the M band enzyme is discussed.

Effect of thyroid hormone on myocardial catecholamine content of the guinea pig

Normal and thyroidectomized guinea pigs were subjected to treatment with either triiodothyronine or thyroid-stimulating hormone. Determinations of myocardial catecholamine content and serum protein-bound iodine revealed a significant increase in myocardial norepinephrine content in the markedly thyrotoxic animal, and a significant decrease in norepinephrine content of the myocardium of hypothyroid animals. The significance of these findings in defining the role of catecholamines in various states of thyroid function is discussed.

Increase of labeled calcium uptake in heart muscle during potassium lack contracture

Analyses of ashed muscle tissue show that the uptake of Ca⁴⁵ by isolated frog heart ventricles from normal Ringer's solution containing 1 mM Ca reaches a maximum value in about 30 minutes of perfusion which is not exceeded after 3 hours of perfusion. The average amount of this labeled Ca taken up from normal Ringer's is 0.7 mM/kg. wet weight of muscle. In contrast to this, the amount of labeled Ca taken up by ventricles perfused with K-free Ringer's increases at a linear rate over a 60 minute period to twice the normal value coinciding with the gradual development of contracture and coinciding with a cellular K loss and Na gain of about 30 mM/kg. How much of the extra labeled Ca taken up from K-free Ringer's represents a net gain in cellular Ca content is not known. However, evidence has been obtained that some of this labeled Ca enters an intracellular compartment. EDTA in K-free Ringer's solution causes relaxation of ventricles in contracture and also renders the muscle fibers indiscriminately permeable. This indicates that a combination of Ca with sensitive intracellular sites is probably the cause of the K lack contracture.