Long-term enhancement of pulmonary gas exchange after high-altitude residence during maturation.

In a previous study, our laboratory showed that young dogs born at sea level (SL) and raised from 2.5 mo of age to beyond somatic maturity at a high altitude (HA) of 3,100 m show enhanced resting lung function (Johnson RL Jr, Cassidy SS, Grover RF, Schutte JE, and Epstein RH. J Appl Physiol 59: 1773-1782, 1985). To examine whether HA-induced adaptation improves pulmonary gas exchange during exercise and whether adaptation is reversible when animals return to SL before somatic maturity, we raised 2.5-mo-old foxhounds at HA (3,800 m) for 5 mo (to age 7.5 mo) before returning them to SL. Lung function was measured under anesthesia 1 mo and 2 yr after return to SL and during exercise approximately 1 yr after return. In animals exposed to HA relative to simultaneous litter-matched SL controls, resting circulating blood and erythrocyte volumes, lung volumes, septal volume estimated by a rebreathing technique, and lung tissue volume estimated by high-resolution computed tomography scan were persistently higher. Lung diffusing capacity, membrane diffusing capacity, and pulmonary capillary blood volume estimated at a given cardiac output were significantly higher in animals exposed to HA, whereas maximal oxygen uptake and hematocrit were similar between groups. We conclude that relatively short exposure to HA during somatic maturation improves long-term lung function into adulthood.     

Analysis of mutation in human cells by using an Epstein-Barr virus shuttle system.

We developed highly sensitive shuttle vector systems for detection of mutations formed in human cells using autonomously replicating derivatives of Epstein-Barr virus (EBV). EBV vectors carrying the bacterial lacI gene as the target for mutation were established in human cells and later returned to Escherichia coli for rapid detection and analysis of lacI mutations. The majority of the clonal cell lines created by establishment of the lacI-EBV vector show spontaneous LacI- frequencies of less than 10(-5) and are suitable for studies of induced mutation. The ability to isolate clonal lines represents a major advantage of the EBV vectors over transiently replicating shuttle vectors (such as those derived from simian virus 40) for the study of mutation. The DNA sequence changes were determined for 61 lacI mutations induced by exposure of one of the cell lines to N-nitroso-N-methylurea. A total of 33 of 34 lacI nonsense mutations and 26 of 27 missense mutations involve G X C to A X T transitions. These data provide support for the mutational theory of cancer.     

Heterologous desensitization of adenylate cyclase with prostaglandin E1 alters sensitivity to inhibitory as well as stimulatory agonists

Adenylate cyclase in cultured human fibroblasts is activated by prostaglandin E1 (PGE1) or beta-adrenergic agonists, e.g., isoproterenol, and inhibited by muscarinic agonists. Incubation with PGE1 reduced adenylate cyclase responsiveness to both PGE1 and isoproterenol; this so-called heterologous desensitization is believed to result from impaired function of the stimulatory guanyl nucleotide-binding protein of the cyclase complex. The effect of heterologous desensitization by PGE1 on inhibition of adenylate cyclase by the muscarinic agonist oxotremorine was examined. Muscarinic inhibition of basal and isoproterenol-stimulated cAMP accumulation was attenuated following exposure to PGE1; the concentration of oxotremorine required for half-maximal inhibition of cAMP accumulation was increased. In both intact cells and membrane preparations the number of binding sites for [3H]scopolamine, a muscarinic antagonist, was unaltered by desensitization. Following exposure to PGE1, receptor affinity for oxotremorine, assessed by competition with [3H] scopolamine, and the guanyl nucleotide sensitivity of agonist binding were reduced. The amount of inhibitory guanyl nucleotide-binding regulatory protein available for [32P]ADP-ribosylation by pertussis toxin was unaltered by desensitization. Thus, heterologous desensitization of adenylate cyclase with the stimulatory agonist PGE1 alters sensitivity to inhibitory as well as stimulatory ligands.     

Bovine serum albumin: characterization of a fatty acid binding site on the N-terminal peptic fragment using a new spin-label

A new spin-label, 4-(L-glutamo)-4'-[(1-oxy-2,2,5,5-tetramethyl-3L-pyrrolidinyl )amino]-3, 3'-dinitrodiphenyl sulfone, is shown to bind to one high-affinity binding site on bovine serum albumin (K = 5 X 10(4) M-1, n = 1). Analysis of the binding of the spin-label to the amino-terminal half (peptic fragment PB) and the carboxy-terminal half (peptic fragment PA) of BSA, and their complex (PA-PB), indicates that the spin-label binds to a long-chain fatty acid binding site located on PB. The usefulness of the novel specificity of the spin-label in characterizing this binding site is discussed.