Action of External Divalent Ion Reduction on Sodium Movement in the Squid Giant Axon

Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm² sec. to 186 pmole/cm² sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.     

Production of the Milk Agent in Cultures of Mouse Mammary Carcinoma

Thin sections of tissue cultures grown from tumors of the RIII high-breast-cancer strain mice were studied in the electron microscope. These tissues contain an abundance of particles whose morphology is consistent with biophysical measurement of the milk agent. These particles, found only extracellularly in our cultures, are formed at the cell membrane. The process of formation, as reconstructed from sections, appears to include a thickening and protrusion of the cell membrane which then evolves gradually into a dense sphere and separates from the cell in much the same manner as does influenza virus. The contents of the newly formed body are later rearranged to form a nucleoid within a membranous sac.     

Oxygen transport during steady-state submaximal exercise in chronic hypoxia

Arterial O2 delivery during short-term submaximal exercise falls on arrival at high altitude but thereafter remains constant. As arterial O2 content increases with acclimatization, blood flow falls. We evaluated several factors that could influence O2 delivery during more prolonged submaximal exercise after acclimatization at 4,300 m. Seven men (23 +/- 2 yr) performed 45 min of steady-state submaximal exercise at sea level (barometric pressure 751 Torr), on acute ascent to 4,300 m (barometric pressure 463 Torr), and after 21 days of residence at altitude. The O2 uptake (VO2) was constant during exercise, 51 +/- 1% of maximal VO2 at sea level, and 65 +/- 2% VO2 at 4,300 m. After acclimatization, exercise cardiac output decreased 25 +/- 3% compared with arrival and leg blood flow decreased 18 +/- 3% (P less than 0.05), with no change in the percentage of cardiac output to the leg. Hemoglobin concentration and arterial O2 saturation increased, but total body and leg O2 delivery remained unchanged. After acclimatization, a reduction in plasma volume was offset by an increase in erythrocyte volume, and total blood volume did not change. Mean systemic arterial pressure, systemic vascular resistance, and leg vascular resistance were all greater after acclimatization (P less than 0.05). Mean plasma norepinephrine levels also increased during exercise in a parallel fashion with increased vascular resistance. Thus we conclude that both total body and leg O2 delivery decrease after arrival at 4,300 m and remain unchanged with acclimatization as a result of a parallel fall in both cardiac output and leg blood flow and an increase in arterial O2 content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression vectors for human adenosine deaminase gene therapy

Somatic gene transfer offers a possible new approach for treatment of human genetic disease. Defects affecting blood-forming tissues are candidates for therapies involving transfer of genetic information into hematopoietic stem cells. Adenosine deaminase (ADA) deficiency is being used as a model disease for which gene transfer techniques can be developed and evaluated. We describe here the construction and testing of 20 retroviral vectors for their ability to transfer and express human ADA in vitro and in vivo via a mouse bone marrow transplantation model. After infection of primary bone marrow with one fo these vectors (p delta NN2ADA), human ADA was detected in 60-85% of spleen colonies at day 14 and maintained long term in the blood of fully reconstituted mice. This system offers the opportunity to assess methods for increasing efficiency of gene transfer, for regulation of expression of foreign genes in hematopoietic progenitors, and for long-term measurement of the stability of expression in these cells.     

The human recombination strand exchange process

A mechanism for the initiation of general recombination that involves the formation of left-handed Z-DNA heteroduplex segments adjacent to right-handed B-DNA heteroduplex segments is discussed. The paranemic nature of this initiation structure allows for homology recognition in the absence of strand cleavage. This model suggests that proteins catalyzing recombination initiation via the formation of paranemic joint should in some capacity recognize Z-DNA. Other studies have shown that both the RecA protein of Escherichia coli and the Rec1 protein of Ustilago maydis have a greater affinity for Z-DNA than B-DNA. Here we have used Z-DNA affinity chromatography to purify a peptide of approximately 120 kilodaltons from a human tumor cell line that catalyzes a simple recombination strand-transfer reaction similar to one developed for the characterization of the RecA and Rec1 proteins. We report details of the characterization of the human strand-transfer activity and identified a potential human recombination complex.     

Plasma concentrations of pituitary hormones in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male rats

Experiments were conducted to test the hypothesis that acute TCDD toxicity is associated with pituitary hypofunction. Sexually mature male Sprague-Dawley rats were given graded doses of TCDD (0-100 micrograms/kg) and evaluated 7 days later. Despite pronounced hypophagia and body weight loss, plasma concentrations of growth hormone (GH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were not significantly affected by any dose of TCDD. Only prolactin (PRL) concentrations were reduced, while, as previously reported, thyroid-stimulating hormone concentrations were elevated. Also, plasma LH, PRL, and adrenocorticotropic hormone (ACTH) concentrations were not significantly affected 1, 2, 3, 4, 5, or 7 days after a single dose of TCDD (50 micrograms/kg). We conclude that (1) pituitary hypofunction is not a major cause of the initial stages of acute TCDD toxicity, (2) growth retardation in TCDD-treated rats is not the result of a deficiency of GH, (3) alterations in plasma corticosterone concentrations are due to altered responsiveness of the adrenal to ACTH stimulation rather than to changes in plasma ACTH concentrations, and (4) that impaired spermatogenesis is not associated with a decrease in plasma FSH concentrations. In addition, the lack of a consistent effect on plasma PRL concentrations suggests that alterations in plasma PRL concentrations do not play a critical role in the toxicity of TCDD. Finally, because TCDD treatment causes a serious androgenic deficiency without increasing the rates at which androgens are catabolized or excreted, the fact that plasma LH concentrations were unaffected indicates that TCDD treatment must reduce the responsiveness of the testis to LH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)