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C Crone

Publications and source records attributed to C Crone.

At least 73 records · Page 4Linked to original sources
PubMed1978

The permeability of single capillaries to potassium ions.

This paper reports a description of methods for determining the diffusional permeability to potassium ions of single capillaries in the frog mesentery. By means of micropipettes, injections or infusions were delivered into a single capillary. The subsequent concentration variations in and about the capillary were followed with K(+)-sensitive microelectrodes. A theoretical analysis is provided which give a quantitative frame of reference for evaluating the observed time-concentration curves in terms of capillary permeability. The advantage of single capillary studies is that the surface area through which diffusion occurs is known as is the concentration difference across the capillary membrane. Three different techniques are: (a) the "single injection" method which represents an application of the indicator diffusion technique where a high-K(+) bolus is injected into a single capillary; (b) the "sack" method which determines the rate of K(+) disappearance from within and immediately outside an occluded capillary segment, after a brief increase in intracapillary K(+) concentration; and (c) the "interstitial diffusion" method which records time and spatial distribution of K(+) in the interstitial space after a step-change in intracapillary K(+) concentration. The methods gave an average potassium permeability of the capillary membrane of 67x10(-5) cm s(-1) (SD: 23, n=26) at room temperature. These figures are clearly higher than those previously reported in mammalian capillary studies using whole-organ techniques. In terms of the pappenheimer pore model, this estimate of capillary permeability is consistent with the behavior of a membrane with a thickness of 1.0 mum which possesses equivalent pores with a radius of 110 A, a fractional pore area of 0.3 percent, and a pore density of 8 mum(-2).

Animals↗
PubMed1977

K+-permeability of the blood-brain barrier, investigated by aid of a K+-sensitive microelectrode.

The K+-permeability of the blood-brain barrier at the capillary level was estimated from determinations of brain extracellular K+-concentration in response to an isotonic bolus containing KCl injected into the carotid artery. A very low permeability appeared from the fact that the extracellular K+-concentration--measured by aid of K+-sensitive microelectrodes--remained unchanged during the passage of the bolus. An upper limit for the blood-brain barrier K+-permeability in the rat was estimated to be 2.8 X 10(-7) cm. with s-1.

Animals↗
PubMed1975

The autoregulation of the microcirculation.

The paper reviews August Krogh's contribution to capillary physiology stressing his formulation of useful new concepts such as "tissue cylinder model", capillary intermittency and the intimate matching of capillary perfusion and cellular metabolism. Looked upon from a control theory viewpoint. Krogh was very early in considering the microcirculation as an autoregulated system with tissue oxygen tension as the controlled parameter. Recent work on Krogh's theories is briefly summarized.

Animals↗
PubMed1975

Induction processes in blood-brain transfer of ketone bodies during starvation.

Fed and starved rats were studied on successive days during a 5-day starvation period. The ability of ketone bodies to pass the blood-brain barrier was estimated by single common carotid injections of labeled ketone bodies and water, and results were expressed as the ratio between the normalized activities of tracers in tissue and blood, the brain uptake index (BUI). BUI of D-3-hydroxybutyrate and acetoacetate decreased as their total concentrations increased in the injectate bolus: BUI of D-3-hydroxybutyrate decreased significantly from 8% at 0.2 mM to 3--4% at 20.2 mM in fed rats and from 11.5% at 0.2 mM to 6% at 20.2 mM in starved rats, indicating saturation of the uptake mechanism. The BUI of both ketone bodies increased significantly with increasing duration of starvation, indicating adaptation to ketonemia. Enzymatic kinetics explained the uptake behavior of D-3-hydroxybutyrate in both fed and starved rats and involved a rise of Km and Vmax during starvation consistent with a doubling of the transport rate at the degree of ketonemia found in starved rats. The uptake of glucose was not influenced by starvation or ketonemia.

Acetoacetates↗
PubMed1970

The penetration of inulin, sucrose, mannitol and tritiated water from the interstitial space in muscle into the vascular system.

1. An isolated gastrocnemius muscle from cat was perfused with a modified Ringer fluid containing the extracellular tracers mannitol, sucrose and inulin and in some cases tritiated water (HTO). When equilibration of the tracers between the perfusate and the tissue was obtained, perfusion with tracer-free fluid was started.2. The fractional rate of escape, Phi (t), of the tracers was followed. For all tracers it declined steadily with time. The rate of decline was faster for the smaller extracellular molecules when any combination of two extracellular tracers was studied.3. Arrest of flow for 1-2 min lead to an increase in Phi (t) for the extracellular tracers when flow was resumed. There was little or no effect upon Phi (t) for HTO.4. Doubling the rate of flow had no effect upon Phi (t) for the extracellular tracers, while that of HTO increased.5. We conclude that the cause of the decline in Phi (t) for the extracellular tracers is concentration gradients in the interstitial space. The findings raise problems in methods for studying capillary permeability by means of the fractional rate of escape of tracers from the interstitial space into the vascular system.

Animals↗