M. McCabe

The Solubility of Oxygen in Erythrocyte Ghosts and the Flux of Oxygen Across the Red Cell Membrane

A composite of partition and diffusion coefficients, together with tissue architecture, controls the movement of oxygen gas within tissues. One aspect of tissue architecture concerns the cell membrane and its role as a possible limiting factor in the flux of oxygen. In general the flux of a solute across a membrane is expressed as a permeability coefficient (due to uncertainties of membrane thickness). The relationship between permeability and diffusion has been discussed by Leib & Stein (1971).

The Measurement of the Diffusion Coefficient of Oxygen Thorugh Small Volumes of Viscous Solution: Implications for the Flux of Oxygen Through Tissues

There is great confusion in the literature concerning the diffusion of oxygen through solutions of high viscosity. Some results suggesting that the Stokes-Einstein relationship does not apply to such small diffusing species. Various attempts at explanation for this have included suggestions of an anomalously increased chemical activity of oxygen in highly concentrated solutions, and/or the possibility of “slip” of the diffusing species in contact with the solvent medium.

Apparent Heterogeneity Between Leukemic Lymphocyte Cell Lines

31P-NMR and polarographic techniques were used to investigate glycolytic versus aerobic oxidative activity in normal and leukemic lymphocytes, and to investigate possible heterogeneity in these parameters between two leukemic cell lines. Molt 3 cells showed a 10-fold higher rate of glutamine-dependent respiration than Molt 4 cells, and an increased level of glutamine-uptake. Molt 3 demonstrated a high intracellular buffering capacity, manifested by constant pHi after addition of glucose, while the same treatment applied to Molt 4 cells induced a change in internal pH of up to 1.23 pH units. This data raises the possibility of heterogeneity of leukemic lymphocytes within the patient from whom the isolation was conducted, or of gross metabolic adaptation by the cell lines in culture.

The Effects of Hypo- and Hyperthermia on the Oxygen Profile of a Tumour Spheroid

The extent of oxygenation of a growing tumour spheroid is a matter of some importance since several different therapies are all significantly affected by the oxygen status of the tumour cells. Additionally hyperthermia has become an additional option as a treatment or adjunct for treatment of tumours.

Studies of Lymph and Lymphocyte Respiration to Estimate Tissue Oxygen Pressures and Oxygen Permeability of the Lymph Duct

It is well established that a mixed peripheral blood lymphocyte population, when subjected to a mitogenic stimulus in vitro, will show a significant increase in glucose consumption which is matched by lactate output. This increased glycolysis has been ascribed to a direct effect of the mitogen upon glucose transport. Less convincing are the reports on the stimulation of oxygen uptake following mitogenic stimuli, however it seems that those reports which indicate an absence of an oxygen uptake stimulation following in vitro mitogenesis (Weidemann and Kolbuch, 1974 and Culvenor and Weidemann, 1976) are the consequence of failure to follow the respiration rate for prolonged periods after the stimulation. It seems that in vitro stimulation of lymphocytes does generate a significant increasein oxygen uptake which is not maximal until about day 3 (Roos and Loos, 1973).

A Simple Fibre Optic Apparatus for Measurement of the Oxy-Haemoglobin Binding Isotherm

We hesitate to report yet another variant of the automatic (polarographic) technique for the determination of the oxy-haemoglobin dissociation curve first described by Longmuir and his colleagues (Franco et al., 1962). Yet it remains true that this method has yet to find much favour since it requires either a considerable preparative effort in the need for a suitable fragmented sarcosomal fraction (Colman & Longmuir, 1963; McCabe, 1973), or (in the variant proposed by Imai et al., 1970) it requires a substantial and dedicating modification of a spectrophotometer (the cutting out of the bottom of the cell housing compartment).

Oxygen Reaction Vessels

Transcutaneous oxygen electrodes were modified to be more suitable as a component of oxygen reaction vessels. The temperature control system was removed from the transcutaneous electrode to decrease the thickness and improve the stability. The temperature control system was incorporated in the metal sleeve surrounding the glass reaction vessel to shorten the distance between the magnetic stirrer and stirring bar, enabling smooth stirring with a short magnetic bar. With these modifications, we have succeeded in reducing the vessel volume to about 0.5 ml, or two to four times smaller than reaction vessels incorporating unmodified transcutaneous electrodes (vessel volume = 1-2 ml) and about twenty times smaller than reaction vessels using rod-shaped Clark electrodes (vessel volume about 10 ml). In another vessels modified as above, two optical guides were connected to the metal sleeve for irradiating the solution and receiving transmitted light simultaneously to enable simultaneous measurements of oxygen concentration absorption spectra. The relationship between oxygen concentration and absorption spectra of Hb is described as an application of this vessel.

Effects of Calcium Channel Blockers on the Respiration of Hela Cells and Hela Mitochondria and the Generation of Oxidising Free Radicals in Tissues Subject to Calcium Imbalance

The profile of oxygen concentration across a sphere of respiring tissue is largely determined by the oxygen consumption (QO2) of the cells in the tissue; other factors such as diffusional constraints imposed by an extracellular matrix, are trivial in comparison with the overriding effect of the parameter for oxygen consumption (McCabe et al., 1979).

A Model for Transmembrane Oxygen Flux by Dipole Oscillation and for Superoxide Extrusion by Phagocytic Cells

Classical theories for the flux of low molecular weight substances across cell membranes conceive of migration as being either dependent on a favourable partition coefficient between aqueous and lipid phases, or as a consequence of diffusion through appropriate holes within the membrane or occurring as a consequence of a reversible binding to a carrier molecule situated within the membrane. It has been suggested from time to time that the transport via a carrier might be accomplished by a rotation of the carrier protein, but there seems to have been little detailed discussion of the possible details and consequences of such a mechanism.

Respiratory gas exchange in ascidans: an almost diffusion limited animal with a cardiovascular system.

The ascidians are a class of the sub Phylum Tunicata, and part of the Phylum Chordata. Characteristically they are sessile marine organisms which have a motile larval stage. They are believed to represent an ancient stock from which other chordates and eventually the vertebrates have evolved. The geometry of the motile (larval) stage and of the ancestral animal is simple in the extreme, supporting the view that this species represents a very early and fundamental form in the evolution of animals. Berrill (1955) has discussed this aspect of the ascidians and has pointed out the evolutionary increase in body size which has occured, from an original animal of less than one mm length, to present day organisms of 10 cm or more. The appearance of a tunic being seen as an adaptation to provide mechanical support and protection for this increased body. The archaic form was a typical diffusion limited animal, whereas it is by no means so obvious that this is so for modern much larger organisms, which possess a cardiovascular system, although rather an unusual one in which the heart regularly and rythmically reverses the direction of flow of blood.