Exposure of the Isolated Frog Skin to High Potassium Concentrations at the Internal Surface : II. Changes in epithelial cell volume,resistance and response to antidiuretic hormone

Isolated frog skin epithelia undergo marked, but reversible swelling when the external skin surface is bathed with conventional NaCl Ringer''s and the internal surface with KCl Ringer''s solutions. In 2 hours, epithelial thickness increased by over twofold. When NaCl Ringer''s was replaced on both sides of the skin, volume returned to control levels in less than 1 hour. When sulfate, rather than chloride, was the predominant anion, exposure of the internal surface to high potassium concentrations did not evoke changes in epithelial cell volume. With both KCl and K₂SO₄ Ringer''s, an immediate drop in DC resistance across the skin occurred. This was followed by partial recovery. Both the immediate drop and partial recovery were unrelated to changes in volume. A slow, sustained secondary drop in resistance was observed with KCl but not K₂SO₄ Ringer''s. This slower drop was associated temporally with swelling. When epithelial cell swelling occurred (i.e. with KCl Ringer''s), the characteristic response of the skin to vasopressin was abolished. However, with sulfate as anion, vasopressin elicited an increase in short-circuit current and/or in cell volume despite high internal potassium concentrations. It is concluded that epithelial swelling increased the permeability of the sodium-selective barrier at the external surface of the cells; and the possibility exists that stretching of cell membranes altered dimensions of pathways through which Na and water move, thereby mimicking the effects of vasopressin.     

Evolution of mammalian X-linked and autosomal Pgk and Pdh E1 alpha subunit genes

The phylogeny and substitution rates of the mammalian X chromosome- located and autosomal phosphoglycerate kinase and pyruvate dehydrogenase genes were investigated. Compatibility analysis was used to show reticulate evolution in these genes. Analysis of the marsupial, mouse, and human phosphoglycerate kinase genes suggests that at least two recombination events have taken place, one occurring about the time of the placental-marsupial split involving exons 1-5 and the other before the primate-rodent split involving exons 9-10. Similar analysis of the pyruvate dehydrogenase genes indicates a recombination event involving exons 2-3 at a time before the primate-rodent split and a gene conversion between exons 3-4 in the human somatic and testis- specific pyruvate dehydrogenase genes after the primate-rodent split. This demonstrates that genetic exchange can occur between paralogous genes at widely separated chromosomal locations. Estimation of nucleotide substitution rates in these genes confirmed a higher substitution rate in the pyruvate dehydrogenase genes. In the phosphoglycerate kinase genes, there is no difference between the substitution rates in mice and humans and between the X chromosome- and autosome-located genes. A greater substitution rate was noted in the mouse autosomal pyruvate dehydrogenase gene when compared with the other mouse and human genes. This may be a result of either directional natural selection or a relaxation of functional constraint at this specific gene.      

Heme oxygenase-1 plays a pro-life role in experimental brain stem death via nitric oxide synthase I/protein kinase G signaling at rostral ventrolateral medulla

Background  

Despite its clinical importance, a dearth of information exists on the cellular and molecular mechanisms that underpin brain stem death. A suitable neural substrate for mechanistic delineation on brain stem death resides in the rostral ventrolateral medulla (RVLM) because it is the origin of a life-and-death signal that sequentially increases (pro-life) and decreases (pro-death) to reflect the advancing central cardiovascular regulatory dysfunction during the progression towards brain stem death in critically ill patients. The present study evaluated the hypothesis that heme oxygnase-1 (HO-1) may play a pro-life role as an interposing signal between hypoxia-inducible factor-1 (HIF-1) and nitric oxide synthase I (NOS I)/protein kinase G (PKG) cascade in RVLM, which sustains central cardiovascular regulatory functions during brain stem death.     

Evaluation of transport pathways for Na+ across frog skin epithelium by means of presteady-state flux ratio

Summary A method is described that makes it possible to separate the sodium fluxes through the isolated frog skin into sets characteristic of the cellular and the paracellular pathway, respectively. If there are two significant pathways for the ion, and if they differ with respect to flux ratio as well as mean passage time, the flux ratios for the individual pathways can be obtained from a set of inward and outward tracer fluxes, covering the time from the addition of the tracers until the achievement of constant fluxes in both directions. Deceased, formerly Department of Ophthalmology, College of Physicians and Surgeons, Columbia University, New York, New York 10032.