Influence of mitochondrial inhibitors on the respiration and energy-dependent uptake of iodide by thyroid slices

The influence of mitochondrial inhibitors, including oligomycin, antimycin and rotenone, on the iodide and oxygen uptake and the nucleotide content of incubated sheep thyroid slices was investigated. Each inhibitor strongly suppressed both iodide and oxygen uptake, and decreased the nucleoside triphosphate content of the slices. In most cases the addition of glucose or mitochondrial substrates restored iodide uptake in inhibitor-treated slices. Inhibitor concentrations sufficient to inhibit iodide uptake strongly had only slight effects on the thyroidal Na(+)+K(+)-activated adenosine triphosphatase. It is concluded that the inhibitors produce their effects by the inhibition in vivo of mitochondrial oxidative phosphorylation. ATP synthesis appears to be essential for iodide uptake to occur, and the high-energy intermediates (or energized state) of oxidative phosphorylation cannot be used to energize the uptake process. To a limited extent glycolytic ATP synthesis can support iodide uptake, which is therefore not exclusively dependent on aerobic metabolism. The mechanism of energy-linked iodide uptake is discussed.     

A MORPHOMETRIC STUDY ON THE THICKNESS OF THE PULMONARY AIR-BLOOD BARRIER

A reliable knowledge of the thickness of the alveolo-capillary "membrane" or air-blood barrier is of physiologic interest since it is intimately related to a quantitative estimation of such functional events as gas diffusion or tissue metabolism in the lung. The characteristic thickness of the air-blood barrier with respect to gas diffusion is its harmonic mean thickness, while the arithmetic mean thickness is related to the mass of tissue building the barrier and consuming oxygen in the lung. Two morphometric methods are proposed by which these two dimensions can be estimated from random measurements in the electron microscope in a reliable, simple, and efficient manner. By applying these methods to three rat lungs the arithmetic mean thickness of the barrier was found to measure 1.25 µ, the harmonic mean thickness, 0.57 µ. On the basis of these measurements a geometric model of the barrier in the form of a corrugated membrane was derived. Its dimensions showed close similarity to those of the natural barrier. This analysis suggested furthermore that the gas conductance of the barrier is nearly optimal if one considers the mass of tissue and the minimal barrier thickness as fixed properties which are determined by other functional requirements on the alveolo-capillary membrane.     

The Entry of Sodium into Human Red Blood Cells in Vivo

The kinetics of sodium, movement into human red blood cells has been studied in vivo with ²⁴Na. When human serum albumin^-131I is used to measure the percentage of plasma trapped in the packed red blood cells after centrifugation, approximately 30 % of red blood cell sodium is found to equilibrate immediately with plasma. It is concluded that this immediately exchangeable compartment of red blood cell sodium is an experimental artefact, associated with the use of labeled albumin for measuring plasma trapping. This immediately exchangeable fraction disappears when sucrose-¹⁴C is used to measure plasma trapping. The experimental results were examined by compartmental analysis, using an analogue computer. The results obtained, when plasma trapping was measured with sucrose-¹⁴C could be simulated by the use of models containing two compartments, arranged in series or in parallel. The errors of the techniques used and the possible physical basis for the results are discussed.     

CA074 methyl ester: a proinhibitor for intracellular cathepsin B.

The specificity of compound CA074 [N-(L-3-trans-propylcarbamoyloxirane-2-carbonyl)-L-isoleucyl-L-pro line] for the inactivation of cathepsin B was quantified in in vitro measurements with cysteine endopeptidases from cattle, it being found that the compound is a very rapid inactivator of cathepsin B (rate constant 112,000 M-1.s-1), with barely detectable action on cathepsins H, L, and S or m-calpain. Conversion of the proline carboxyl group of the inhibitor to the methyl ester virtually abolished the effect on cathepsin B, and a possible explanation for the importance of the carboxyl is presented on the basis of the tertiary structure of cathepsin B. It was found that CA074 methyl ester (1 microM, 3 h) caused selective inactivation of the intracellular cathepsin B of human gingival fibroblasts in culture, in contrast to other available agents, and we suggest that CA074 methyl ester will be of value in the elucidation of the biological functions of cathepsin B.