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Biomedical subjects

M B Visscher

Publications and source records attributed to M B Visscher.

At least 37 records · Page 2Linked to original sources
PubMed1972

Calcium ions and the cardiotonic action of glucagon (calcium fluxes-myocardial function-asystole-membrane transport-cat).

The positive inotropic action of glucagon on the cat heart is dependent upon the extracellular Ca concentration. The inotropic effect is proportionately greater, the lower the concentration of Ca in the perfusate (above zero, at which glucagon is without significant effect). Nevertheless, Ca influx (as measured with (45)Ca) into the myocardium is not demonstrably influenced by glucagon, except at 0.09 mM Ca, where the interpretation of the effect is complicated by the fact that there is mechanical asystole at that Ca concentration in the absence of glucagon, while excitation-contraction coupling still occurs when the hormone is added. The possibility is suggested that glucagon may influence intracellular movement of Ca, even when its transmembrane movement is affected only slightly.

Animals↗
PubMed1971

Coronary blood flow, oxygen delivery rate and cardiac performance.

1. Studies have been made on the isolated blood-perfused heart of dogs in which isometric tension development at various settings of resting tension (RT) was measured at various levels of O(2) delivery rates controlled by altering (a) coronary blood flow (CBF), (b) O(2) capacity or (c) O(2) saturation of the perfusate. Measurements were also made of O(2) consumption and vascular perfusion resistance.2. The capacity of the left ventricle to develop tension at any given setting of resting tension was found to be directly correlated with changes in O(2) delivery rate using any of the above three methods of altering the latter.3. The slopes of the curves relating resting tension to developed tension are positively correlated with total O(2) delivery to the heart.4. The O(2)-dependent metabolic effect upon tension production was found to be slow in development, in contrast to the Frank-Starling effect, which reached full development in the first heart beat after a change in resting length and tension.5. The O(2) consumption of the isometrically contracting heart is strongly correlated with the O(2) delivery rate at all particular values of resting tension and related developed tension.6. The metabolic state of the myocardium as determined by the rate of O(2) delivery within physiological ranges is (a) a direct major determinant of the tension-producing capacity of the heart muscle and (b) determines the magnitude of adaptation via the Frank-Starling mechanism.

Animals↗
PubMed1970

Influx of calcium into rabbit myocardium in relation to its ionic environment.

In the first 150 seconds after contracture of rabbit myocardium has been induced by shifting from perfusion with zero [Ca(2+)] and low [K(+)] to solutions with normal levels of those cations, there is a large influx of Ca(2+) as measured both by isotopic tracer flux and by total tissue [Ca]. Tracer studies indicate that the influx is 90 per cent complete in 90 seconds. Contracture due to substitution of either Li(+) or K(+) for Na(+) in perfusion fluids is also associated with an increased influx, but of lesser magnitude. The latter types of contracture are reversible while the former is not. It seems probable that the irreversible contracture is induced by the large Ca(2+) influx.

Animals↗