Comparative study on the effects of exogenous palmitate and erucate on intracellular electric properties of cultured beating heart cells

Digitalis-like compounds in animal tissues

The Na+, K+ activated adenosine triphosphatase is present in the membrane of eukaryotic cells and represents a major pathway for Na+ and K+ transport across the plasma membrane. Cardiac glycosides such as ouabain or digoxin suppress this enzyme activity by binding to a specific receptor on the membrane. Studies conducted in this and other laboratories have proven the existence of digitalis-like compounds in animal tissues which may serve as in vivo regulators of the Na+, K(+)-pump activity. This review summarizes the attempts to identify these compounds from animal tissues and examines the potential physiological role of some of the identified compounds.

Relationship between reestablishment of sarcolemma-glycocalyx ultrastructures and restoration of transmembrane potentials in cultured rat heart cells

Simultaneous studies on sarcolemma-glycocalyx ultrastructures and electrophysiological properties of the trypsin-released rat heart cells were carried out in order to define the relationship between sarcolemmal membrane repair and transmembrane potential recovery in the long-term cultured heart cells. Based on electron microscopic observations of the trypsinized heart cells maintained in the long-term culture, serial alterations of sarcolemma-glycocalyx complex could be divided into three successive stages. A defective stage of the sarcolemma-glycocalyx complex was present in the cultured cells between day 3 and day 6 of incubation. A repaired stage of the sarcolemma-glycocalyx complex was observed in the cells from day 7 to day 9 of incubation. A well-organized stage of the sarcolemma-glycocalyx complex was seen in the cells after ten days of incubation. Sequential measurements of electrophysiological parameters of the cultured heart cells showed a diphasic evolution of maximum diastolic potential and action potential amplitude, with an initial decrease from day 3 to day 9 of incubation and a later return to normal range after ten days of incubation. There seemed a good correlation between electrophysiological properties and sarcolemma-glycocalyx ultrastructures. Thus, we conclude that restoration of the electrophysiological properties of the cultured cells is closely related to the reorganization of the defective sarcolemmal membrane.

A simple gas-flow chamber for cultured cell electrophysiology in a controlled atmosphere

A simple and inexpensive device is described to control the gaseous environment while recording membrane potentials and contractile motion from single cultured cells. This equipment was used to study the electrophysiological and mechanical responses to hypoxia of cultured rat heart cells, but should also be suitable for a wide range of applications with several cell types.

Effect of change in growth environment on cultured myocardial cells investigated in a standardized medium

Neonatal rat heart cells cultivated in either of two different media which varied only in their serum supplements were transferred to chemically defined medium (Ham's F10) for 24 h before measuring a variety of parameters. The 24-h period of exposure to chemically defined medium was not sufficient to reverse the effects imposed on the cells by the serum used in the first phase of growth. The cells differed in rate and duration of action potentials and contractions. The initial serum composition affected the response of the cells to calcium deficiency. Studies involving the effects of pharmaceutical reagents such as isoproterenol were also influenced by the serum. In attempting to determine the cause and possible mechanism, it was found that mitochondrial membrane permeability for nitroblue tetrazolium (NBT) was unchanged. Although the serum supplements differed in fatty acid composition, the fatty acid profiles of the cell phospholipids were relatively constant. We conclude that the function of the cells is affected by the growth environment, particularly serum; that a short exposure to a uniform chemically defined medium is not sufficient to reverse these effects; and that the differences in effects are not the result of changes in the fatty acid composition of the whole cell phospholipids nor in mitochondrial membrane permeability as measured by NBT.

A search for an 'ouabain-like' substance from the electric organ of Electrophorus electricus which led to arachidonic acid and related fatty acids

The electric organ of Electrophorus electricus contains substances which inhibit (Na+ + K+)-ATPase activity, the specific binding of [3H]ouabain to purified (Na+ + K+)-ATPase and 86Rb+ uptake by chick cardiac cells in culture. The active organic material was extracted from microsomal membranes. Its purification was carried out by chromatography on Sep-Pak C-18 and thin-layer chromatography. Reverse-phase liquid chromatography and mass spectrometry identified the active material as a mixture of unsaturated fatty acids. Linoleic (18:2), arachidonic (20:4), linolenic (18:3) and docosahexaenoic acids (22:6) contributed to about 60% of the total activity of the active material. The other active substances could be arachidonic analogs, since they have both a lipophilic and carboxylic character. Pure unsaturated fatty acids have been shown to be active in the different biological assays used to analyze the endogenous 'ouabain-like' activity. Linolenic, arachidonic and docosahexaenoic acids were the most active, whereas saturated fatty acids and glyceryl esters or methyl esters of unsaturated fatty acids were inactive. It is possible that in pathological situations in which the level of unsaturated fatty acids increases, these molecules may then act as physiological inhibitors of the sodium pump.