Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium

Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel.     

Temperature sensitivity of potassium flux into red blood cells in the familial pseudohyperkalaemia syndrome

The temperature dependence of potassium flux into the red cells of normal and pseudohyperkalaemic individuals over the range 4-40 degrees C was measured using 86RbCl as tracer. Flux through the pump was measured as the ouabain-sensitive component (0.2 mM ouabain) and flux via Na+,K+-cotransport was measured as the decrease in the rate of K+ influx in the presence of 1 mM furosemide. The residual passive permeability of the red cell plasma membranes to K+ was that influx which was unaffected by either inhibitor. When Na+ influxes were measured, the ratio of Na+ to K+ transported via the furosemide-sensitive component was 1 over the full temperature range studied. The temperature sensitivity of K+ influx via the pump was normal as was the enzymic activity of the Na+,K+-ATPase. In contrast, the activity of the Na+,K+-cotransport system in pseudohyperkalaemics was more temperature sensitive than that of controls and affected individuals also showed a greater passive permeability to K+ at low temperatures. Red cell membranes from affected individuals have significantly increased amounts of phosphatidylcholine which are balanced, to a degree, by a decreased content of phosphatidylethanolamiane. It is proposed that in this example of familial pseudohyperkalaemia there is an alteration in the structure of the red cell plasma membrane which influences the temperature sensitivity of both its cotransport and passive permeability properties.     

The involvement of a rhodopsin-like photopigment in the photoperiodic response of the Japanese quail

Summary A technique has been developed for the investigation of the photopigment involved in the photoperiodic control of reproduction in Japanese quail,Coturnix coturnix. When these photoreceptors were exposed to white or monochromatic light a clear relationship was found between light intensity and the extent of photo-induced luteinizing hormone (LH) secretion. A spectroradiometric investigation of the passage of light through the skull and brain enabled us to illuminate the hypothalamic region with equal numbers of photons at a range of wavelengths. Action spectra were then conducted and showed a photopigment with a peak sensitivity at wavelengths near 500 nm. An excellent match was obtained when the standard absorption spectrum for a rhodopsin was fitted to the action spectrum, suggesting a rhodopsin maximally sensitive at 492 nm. The absolute sensitivity of the photoreceptors was calculated at a range of wavelengths: with light at 500 nm, 2.85×10^–12 E·cm^–2·s^–1 triggered the photoperiodic response. This level of sensitivity is matched only by the rhodopsin visual pigments.Abbreviations LH luteinizing hormone - T transmission     

Reproductive endocrinology of the Black-browed albatross Diomedea melanophris and the Grey-headed albatross D. chrysostoma

Gonadal size and the circulating concentrations of two pituitary hormones (luteinizing hormone and prolactin) and three gonadal steroids (testosterone, progesterone and oestradiol-17β) were measured in two closely related Diomedea albatrosses at South Georgia. The Grey-headed albatross D. chrysostoma , if successful in rearing a chick, usually breeds biennially, whilst the Black-browed albatross D. melanophris normally breeds annually. Direct examination (by laparoscopy) of the gonads showed that the testes of both species underwent annual cycles, whilst endocrine data confirmed that those male Grey-headed albatrosses at the colony in the pre-laying period but not breeding in that year (having bred successfully the previous year) were apparently in full reproductive condition with elevated testosterone levels typical of breeding birds. However, the females of the two species differed markedly. Grey-headed albatrosses, in a year following successful breeding, had undeveloped ovaries with low levels of circulating oestradiol but high levels of progesterone, whereas the Black-browed albatrosses showed a pattern consistent with annual ovarian development. The profiles of gonadal steroids through the breeding season were similar for the males of both species but differences existed between the females. In the female Grey-headed albatrosses, transient peaks of progesterone were present throughout chick rearing but these were absent from Black-browed albatrosses. Prolactin had a similar profile in both species, with uniformly high levels throughout incubation and a rapid fall near the end of the brood-guard period. It is suggested that Grey-headed, like Black-browed, albatrosses are intrinsically annual breeders. However, if a female Grey-headed albatross breeds successfully in one year, then nutritional factors operate to ensure that in the following year the female does not show ovarian development, although the ovary is active in terms of progesterone secretion.     

Respiratory syncytial virus ts mutants and nuclear immunofluorescence.

A replicated sector-plating procedure was used to isolate 35 induced temperature-sensitive (ts) mutants and one spontaneous ts mutant from a wild-type stock of respiratory syncytial (RS) virus cloned from recent clinical material. Seven of these mutants were ts for plaque formation at 37 degrees C as well as at the restrictive temperature of 39 degrees C. The wild-type strain did not differ markedly from standard laboratory strains of RS virus. It was dependent on exogenous arginine (84 mug/ml) for optimal growth, and was not significantly inhibited by mitomycin C (10 mug/ml). It was sensitive to actinomycin D (2.5 mug/ml) during the early part of the growth phase. A characteristic focal cytopathic effect was obtained in BS-C-1 cells. Staining of infected monolayers by an indirect immunofluorescence procedure revealed a profusion of filamentous processes extending from the plasma membrane, and a similar modification of the surface of infected cells could be visualized by scanning electron microscopy. Filament production was inhibited when certain ts mutants were incubated at 39 degrees C, confirming the virus-specific nature of the phenomenon. Thirty-four of the mutants were classified into three groups by immunofluorescence. Complementation was observed in mixed infection with a single mutant from each group. Nuclear, as well as cytoplasmic, immunofluorescence was detected in RS virus-infected cells using a high-titer bovine anti-bovine RS virus serum. Visualization of nuclear antigen was dependent on the inhibition of cytoplasmic fluorescence obtained when ts mutants in groups I and III were incubated at restrictive temperature.     

Plasma luteinizing hormone during the breeding cycle of the female ring dove

Plasma luteinizing hormone (LH) levels in serial blood samples of female ring doves (Streptopelia risoria) were measured by radioimmunoassay method. Our findings indicate the following pattern of LH levels: LH increases during early courtship which reaches a peak (5.43 ± 0.79 ng/ml) during the nesting period. LH declines following egg-laying (3.77 ± 0.33 ng/ml) and again after hatching (2.23 ± 0.28 ng/ml). It remains high in females which laid infertile eggs initially and subsequently showed a further laying. The results are compared with published data on plasma estrogens and progesterone in the dove's breeding cycle.     

Action of Interferon in Enucleated Cells

Interferon induces protection of enucleated BSC-1 cells against infectious vesicular stomatitis virus production if cells are treated before, but not after, enucleation.     

Absorption and retinol equivalence of beta-carotene in humans is influenced by dietary vitamin A intake

The effect of vitamin A supplements on metabolic behavior of an oral tracer dose of [14C]beta-carotene was investigated in a longitudinal test-retest design in two adults. For the test, each subject ingested 1 nmol of [14C]beta-carotene (100 nCi) in an emulsified olive oil-banana drink. Total urine and stool were collected for up to 30 days; concentration-time patterns of [14C]beta-carotene, [14C]retinyl esters, and [14C]retinol were determined for 46 days. On Day 53, the subjects were placed on a daily vitamin A supplement (10000 IU/day), and a second dose of [14C]beta-carotene (retest) was given on Day 74. All 14C determinations were made using accelerator mass spectrometry. In both subjects, the vitamin A supplementation was associated with three main effects: 1). increased apparent absorption: test versus retest values rose from 57% to 74% (Subject 1) and from 52% to 75% (Subject 2); 2). an approximately 10-fold reduction in urinary excretion; and 3). a lower ratio of labeled retinyl ester/beta-carotene concentrations in the absorptive phase. The molar vitamin A value of the dose for the test was 0.62 mol (Subject 1) and 0.54 mol (Subject 2) vitamin A to 1 mol beta-carotene. Respective values for the retest were 0.85 and 0.74. These results show that while less cleavage of beta-carotene occurred due to vitamin A supplementation, higher absorption resulted in larger molar vitamin A values.