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L J THOMAS

Publications and source records attributed to L J THOMAS.

At least 19 recordsLinked to original sources
PubMed1965

THE EFFECTS OF ZINC ON CONTRACTILITY, MEMBRANE POTENTIALS, AND CATION CONTENT OF RAT ATRIA.

Zinc depresses the contractile force of electrically driven rat atria logarithmically with time. The threshold concentration is about 5 x 10(-6)M zinc and the half-time for contractile depression at 10(-4)M is about 25 minutes. Zinc also depresses spontaneous activity of atria and alters the transmembrane potential parameters in a manner similar to quinidine. Unlike quinidine, zinc causes an elevation of the resting potential and an elevation of cellular potassium which varies with time in the same way as the resting potential. Exposure to 10(-4)M zinc for 60 minutes causes a statistically significant fall in atrial calcium content and an amount of radioactively labeled zinc is taken up which is quantitatively equal to the calcium lost. Zinc has no effect on rigor caused by iodoacetate but inhibits rigor caused by 1-fluoro-2,4 dinitrobenzene. It is postulated that zinc depression of contractile force is not due to metabolic inhibition, probably not due to quinidine-like action on the cell membrane, but may be due to an interference in the handling of calcium by the cell.

Calcium↗
PubMed1960

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

Analyses of ashed muscle tissue show that the uptake of Ca(45) 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.

Calcium↗