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Biomedical subjects

L Bass

Publications and source records attributed to L Bass.

71 records · Page 4Linked to original sources
PubMed1970

An electrochemical model for depolarization of a retinula cell of Limulus by a single photon.

The response of a visual cell in the eye of Limulus is treated mathematically in terms of a model derived from the properties of excitable nerve membranes. Electron microscopic sections of the rhabdomere indicate that its structure is a close-packed array of cylindrical tubules, the interiors of which communicate with the retinula cell cytoplasm, while the external interstitial fluid is a conducting medium continuous with the extracellular space of the ommatidium. If a single highly conducting channel is opened in this membrane structure, it can be shown how the excitation can spread to depolarize the retinula cell by several millivolts. Intense activity of "sodium pumps" in the rhabdomal membrane would be required to maintain the ionic concentrations in the interstitial fluid.

Animals↗
PubMed1968

Enzyme activities in polarized cell membranes.

The theoretical pH dependence of enzyme activities in membranes of low dielectric constant is estimated. It is shown that in biological membranes some types of enzymes may attain a limiting pH sensitivity such that an increment of only 0.2 pH unit (sufficient to induce action potentials in squid axons) causes a relative activity change of over 25%. The transients of enzyme activity generated by membrane depolarization and by pH increments in the bathing solution are discussed in relation to the transients of nervous excitation.

Action Potentials↗
PubMedDate not supplied

A method of determining intrinsic hepatic clearance from the first-pass effect.

1. The relation between systemic hepatic clearance, intrinsic hepatic clearance and hepatic blood fow is considered from the point of view of the sinusoidal perfusion (parallel tube) model of the liver. 2. It is shown how intrinsic hepatic clearance may be calculated, for substrates eliminated in the liver and the kidney only, from data obtained by introducing successively an oral and an intravenous dose (i.e., by using the first-pass effect) with the clinically cumbersome catheterization of the liver vein. 3. The rate of hepatic blood flow is shown to follow from the same data.

Animals↗
PubMedDate not supplied

Extended theory of the early diffusion of multiple indicators: bounds on permeability ratios, with applications to intestinal capillaries.

The determination of ratios of capillary permeabilities to multiple indicators is secured by constructing upper bounds on effects of early back-diffusion following a single arterial injection. The analysis does not exclude highly extracted indicators, and it allows for effects of asymmetric blood-tissue exchange and of tissue concentration gradients. The concept of flow limitation of uptake is delimited operationally. It is shown how to identify effects of heterogeneity of uptake for data sets extended over large ranges of rate of blood flow. These new methods are used to show, for several sets of previously published data from muscle, that back-diffusion cannot change appreciably the permeability ratios determined previously without any quantification of back-diffusion. The main application is to data published by Perry and Granger (1981) on the permeability of cat intestinal capillaries to raffinose and inulin. The permeability ratios deduced from these data imply paradoxically restricted diffusion; it is shown that this cannot be attributed to effects of back-diffusion, heterogeneity of extraction, or of solvent drag. It is shown that the paradox is removed if tissue-to-blood permeability to raffinose is at least double the blood-to-tissue permeability, possibly as part of the active transport of sugars from the intestinal lumen. It is shown that corresponding results on permeability ratios in dog gastric capillaries are not paradoxical (against the standard of unrestricted diffusion) under symmetric permeability to raffinose.

Animals↗
PubMedDate not supplied

A comparison of hospice in the UK and the US.

This article presents a comparison of hospice services in the United Kingdom and the United States. The article includes a brief history of the development of the modern hospice movement in the United States and the United Kingdom, with emphasis on funding, regulatory standards, and demographics.

Cross-Cultural Comparison↗