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Biomedical subjects

R F Burton

Publications and source records attributed to R F Burton.

36 records · Page 2Linked to original sources
PubMed1972

The antagonistic actions of calcium and magnesium on the superfused ventricle of the snail Helix pomatia.

1. The isolated, superfused half-ventricle of the snail (Helix pomatia) maintains a degree of tonic activity even when not beating, since the membrane is depolarized beyond the tension threshold. Beating may be initiated by lateral stretch of the ventricle and by 5-hydroxytryptamine.2. Ca and Mn each have a hyperpolarizing action, while K and to a lesser extent Na cause depolarization: the tonic activity of the ventricle is affected accordingly.3. An increase in the extracellular concentration of Mg also causes the tension to fall, but without change in membrane potential. It can also initiate beating.4. Contractures induced by 30 mM-K are steadily maintained, but start with a more-or-less distinct twitch-like contraction. A contracture induced by a concentration of K above about 50 mM is poorly sustained and is followed by a further brief contracture when the K concentration is reduced to normal.5. Relations between contracture tension and the concentrations of Ca and Mg accord with the hypothesis that the two ions compete for attachment to a binding site on the cell surface and that tension is proportional to the amount of bound Ca. On this hypothesis, the apparent dissociation constant of the Mg complex is 11.4 mM and that of the Ca complex 0.15 mM or less.6. This effect of Mg is like that of Na on frog ventricle and some of the differences in the behaviour of snail and frog ventricles are abolished by appropriate adjustment of the extracellular concentrations of these ions.

Animals↗
PubMedDate not supplied

Differences in pH between interstitial fluid and arterial blood in water-breathing and air-breathing vertebrates.

Most cells are bathed by interstitial fluid, but extracellular pH measurements are mostly for arterial plasma. Whole-body mean pH differences between the two fluids have been estimated in terms of a simple model. This relates to the diffusive exchange of carbon dioxide and oxygen and utilizes literature data, for 22 vertebrate species, on arterial and mixed-venous tensions of both gases. Uncertainties arise because the carbon dioxide reaction in blood may sometimes be in disequilibrium and because carbon dioxide diffusion is facilitated to unknown degrees in the presence of buffers. Nevertheless, the model suggests that the pH difference should tend to vary inversely with arterial carbon dioxide tension. In some species, this may aid interstitial pH homeostasis, but a clearer implication is that the difference should be generally greater in water breathers than in air breathers. It has previously been found that arterial pH in water-breathing teleosts also tends to be higher than in air-breathing tetrapods (when allowance is made for temperature and plasma sodium concentration) and to a comparable extent. Thus, mean interstitial pH may be more nearly similar in the two groups than is arterial pH. Direct measurements of interstitial pH do not yet suffice to test the model.

Air↗