Temporal patterning of feeding by hummingbirds

For five species of hummingbirds in the laboratory, time between meals was related to energy intake on the first meal and rate of energy expenditure between meals. Field observations gave similar results. Average meal sizes were similar at one intake rate independent of food caloric density; females averaged longer bouts than males. When rate of intake was approximately halved, meal duration approximately doubled and volume intake remained similar. We postulate that feeding is initiated when crop contents reach a lower threshold and that feeding is terminated after ingestion of an optimal volume determined by the added weight of the meal.     

Ascorbic acid uptake in guinea pig intestinal mucosa

Cellular accumulation of ascorbic acid was investigated in vitro in distal intestinal mucosa of guinea pig. With ¹⁴C-ascorbic acid present at 8 μM/L in the bathing media, tissue/media (T/M) concentration ratios of at least 5 were routinely achieved. Recently absorbed ascorbic acid appeared to be free in solution in the cellular fluid in that it diffused from tissue exposed to poisons with a disappearance half-time of approximately 10 minutes. Ascorbic acid uptake was highly dependent on the presence of sodium in the bathing media; total Tris substitution resulted in a 97% decrease in uptake. Also, metabolically depleted tissue did not accumulate ascorbic acid against a concentration gradient. Uptake of ¹⁴C-ascorbic acid from a bathing solution concentration of 8 μM/L was reduced 67% in the presence of 0.8 mM/L nonlabeled ascorbic acid. Recently absorbed ¹⁴C-ascorbic acid moved more rapidly back into the lumen when the luminal solution contained nonlabeled ascorbic acid (5 mM) than when it contained mannitol (5mM). This demonstration of counter transport substantiates a carrier mechanism in the brush border.     

The isolation and characterization of TabR bacteria: Hosts that restrict bacteriophage T4 rII mutants

Summary We have isolated mutants of Escherichia coli B (called TabR) that restrict the growth of bacteriophage T4 rII mutants at high temperature. TabR strains lysed very rapidly after infection with rII mutants, and no progeny phage were produced. T4⁺-infected TabR cells also lysed quickly, but the cells remained intact long enough to give a small burst. We have selected pseudorevertants of rII deletion mutants that grow on TabR at high temperature; tk (thymidine kinase) is a component of one class of these pseudorevertants.T4 strains harboring mutations in genes 12, 16, 25, 34, 36, 45 and 63 were also specifically restricted on TabR strains at high temperature. Bacteriophages T2, T4, T5, T6, and T7 grew normally on TabR, while , 80, and P1 failed to grow at any temperature. The most restrictive TabR strains were auxotrophic for methionine at high temperature, and most spontaneous Met⁺ revertants had also lost the ability to restrict rII mutants, suggesting that the TabR phenotype and methionine auxotrophy result from the same mutation.Although the mechanism by which TabR strains exert their restriction has not been determined, one model is described. The potential uses of these and similar strains is discussed.     

Miniature Ag−AgCl electrode for voltage clamping of theAmbystoma collecting duct

Summary We have developed a miniature silver-silver chloride electrode. The outer diameter of the electrodes averaged 22 m and the input resistance 8.8 k. Since the core of the electrode is a glass fiber, the problem of the extreme malleability of a small diameter silver fiber is circumvented. The properties of the electrode permit us to insert it into short (600 m) fragments of the amphibian collecting duct while they are being perfusedin vitro. The passage of currents in the range of 0 to 6×10^–8 amperes allowed us to voltage clamp the nephron fragment between +20 and –20 mV. The current-voltage plots are linear over this range. Two lines of evidence suggest that the voltage clamp is homogeneous. First, the voltage measured at the perfusion end during a voltage-clamp experiment of the tubule is not significantly different from that measured at the collecting end. Secondly, the specific resistance of collecting ducts estimated from the core conductor analysis is 3.3±0.8×10⁴ cm, a value not significantly different from that computed from the current-voltage plots as determined with the Ag–AgCl electrode, 3.0±0.5×10⁴ cm. This method permits precise control of both the ionic and electrical gradients across fragments of the amphibian collecting duct.     

DISAGGREGATION OF POLYSOMES IN FETAL ORGANS AND MATERNAL BRAIN AFTER ADMINISTRATION OF d-LYSERGIC ACID DIETHYLAMIDE IN VIVO

The intravenous administration of d-lysergic acid diethylamide (LSD) to pregnant female rabbits induced hyperthermia as well as disaggregation of polysomes in fetal organs and maternal brain. The LSD-induced polysome shift in maternal brain and fetal organs was not due to an activation of ribonuclease or associated with alterations in the levels of free amino acids. Pretreatment with the receptor blocking agents haloperidol and pizotyline blocked both LSD-induced polysome shift in maternal brain and fetal organs and LSD-induced hyperthermia. Fine dissection of adult rabbit brain showed that the extent of LSD-induced disaggregation of polysomes does not exhibit any marked regional variation.     

Mice with Spontaneous Mammary Tumors Develop Type-Specific Neutralizing and Cytotoxic Antibodies Against the Mouse Mammary Tumor Virus Envelope Protein gp52

Sera from C3H mammary tumor-bearing mice contain cytotoxic antibodies for mouse mammary tumor virus (MMTV)-producing cells, based on (51)Cr release in a complement-dependent serum cytotoxicity assay. The cytotoxic antibodies could be absorbed by purified C3H MMTV gp52 and C3H MMTV-infected cat cells (C3H [MMTV] CrFK) containing cell surface MMTV gp52. However, purified MMTV p27 and uninfected CrFK cat cells were negative. Absorption of the sera with GR (MMTV) CrFK cells also removed all of the cytotoxicity, whereas absorption with RIII (MMTV) CrFK cells was negative, even though all three infected cat cells contained equivalent amounts of gp52. The same C3H cytotoxic sera also neutralized the focus-forming capacity of a C3H MMTV pseudotype of Kirsten sarcoma virus containing MMTV gp52. In contrast, sera from mammary tumor-bearing GR and RIII mice did not neutralize the pseudotype. Furthermore, neutralization could be achieved only by anti-gp52 but not by anti-gp36, -p27, -p14, or -p10 C3H MMTV sera. The gp52's of C3H, GR, and RIII MMTV could also be distinguished by using a type-specific competition radioimmunoassay employing (125)I-gp52 of C3H MMTV and a hyperimmune rabbit anti-C3H MMTV serum. To demonstrate these differences directly, we studied the primary structure of gp52 on the surface of the C3H, GR, and RIII (MMTV) CrFK cells. Two-dimensional tryptic peptide maps of the cell surface lactoper-oxidase-catalyzed iodinated gp52's revealed a greater number of peptides common to the gp52's of C3H and GR MMTVs than to RIII MMTV gp52. These results demonstrate that gp52 is a major target antigen for both cytotoxic and neutralizing antibodies, that the cell surface and virion-associated gp52's of C3H, GR, and RIII MMTV contain both group- and type-specific determinants, and that C3H and GR MMTV gp52's are antigenically more related to each other than to RIII MMTV gp52. Furthermore, C3H mammary tumor-bearing mice develop type-specific antibodies capable of recognizing unique gp52 determinants and, therefore, are able to distinguish the gp52 of C3H MMTV from the gp52's of GR and RIII MMTV.     

Defluorination of fluoroacetate in the rat

Rats given 5 ppm F as FAc (equivalent to 26 ppm of NaFac) in the drinking water for approximately four months deposited as much fluoride in the skeletal system as did rats receiving 5 ppm F as NaF in the water. Little evidence could be found for the presence of organically bound fluoride in bone after ingesting FAc, though an appreciable proportion of skeletal fluoride deposited when NaF was ingested was shown not to respond to the fluoride ion electrode. The daily urinary excretion of total fluoride after FAc was somewhat greater than after NaF; about two thirds of this fluoride responded to the electrode, whereas more than 90 percent of the total fluoride after NaF was ionic in nature. The data are interpreted as showing that the rat is capable of splitting the C-F bond in FAc and/or in its fluoride-containing metabolites, with subsequent skeletal storage and renal excretion of the released fluoride ion. The chronic administration of this low level of FAc caused an early but temporary retardation of growth. The Krebs cycle was interfered with, as evidenced by increased concentrations of citrate in the kidney and urine. At termination of the experiment, histological examination of the testes showed that the FAc had induced severe damage characterized by massive disorganization of the tubules, nearly total loss of functional cells, absence of sperm, and damage to the Sertoli cells.