The carboxyl terminus of the hamster beta-adrenergic receptor expressed in mouse L cells is not required for receptor sequestration

The structural basis for agonist-mediated sequestration and desensitization of the beta-adrenergic receptor (beta AR) was examined by oligonucleotide-directed mutagenesis of the hamster beta AR gene and expression of the mutant genes in mouse L cells. Treatment of these cells with the agonist isoproterenol corresponded to a desensitization of beta AR activity. A mutant receptor that bound agonist but did not couple to adenylate cyclase showed a dramatically reduced sequestration response to agonist stimulation. In contrast, beta AR mutants in which the C-terminus was truncated and/or in which two regions that have been proposed as phosphorylation substrates for cAMP-dependent protein kinase were removed showed normal sequestration responses. These results demonstrate that agonist-mediated sequestration of the beta AR can occur in the absence of the C-terminus of the protein and reveal a strong correlation between effective coupling to Gs and sequestration.     

RU486 is not an antiprogestin in the hamster

The biological activity and progestin receptor binding activity of the synthetic steroid RU486 (RU38486; 17-beta-hydroxy-11-beta-(4-dimethylaminophenyl)-17-alpha-(1-propynl++ +)- estra-4,9-diene-3-one) were investigated in the hamster. RU486 demonstrated no antiprogestational activity in the female hamster in that it was ineffective in blocking decidualization or interrupting early pregnancy. Competitive binding assays showed RU486 did not compete from hamster uterine progestin receptor. It is concluded that hamster uterine progestin receptor has unique steroid binding specificity.     

Hypothyroidism in rats does not lower mitochondrial ADP/O and H+/O ratios.

We investigated reports that mitochondria isolated from hypothyroid rats have decreased ADP/O and H+/O ratios. We observed no decrease in the H+/O ratio in mitochondria from hypothyroid rats, in the presence of either 2% (w/v) fatty-acid-free bovine serum albumin or 100 nM free Ca2+. The ADP/O ratio in mitochondria isolated from hypothyroid rats in the presence of 2% fatty-acid-free bovine serum albumin was measured. Under normal experimental conditions we found no decrease in the ADP/O ratio, relative to that measured for littermate controls. At the low concentrations of mitochondrial protein used in the previously reported studies, the ADP/O ratio of mitochondria from hypothyroid rats was decreased, whereas that for control rats was only slightly decreased. The difference between the ADP/O ratios measured for mitochondria form hypothyroid rats and from control rats under these conditions was eliminated by inhibition of endogenous adenylate kinase. We suggest that the lowering of the apparent ADP/O ratio in mitochondria from hypothyroid rats at low concentrations of mitochondrial protein is an experimental artefact resulting from the breakdown of ADP to AMP.     

Distribution of type A spermatogonia in the mouse is not random

The distribution of type A spermatogonia was studied using drawings of cross-sectioned tubules at various stages of the spermatogenic cycle of perfusion-fixed, epoxy-embedded mouse testis. Spermatogonia were classified as either positioned opposite the interstitium or opposite the region where two tubules make contact or in a defined, intermediate region at which the two tubules diverged. At stage V, the population of type A spermatogonia, comprised of A(s) through A(al) cells, is randomly positioned around the periphery of the seminiferous tubule. The A(s) through A(al) population becomes nonrandomly distributed beginning at stage VI, being located primarily in regions where the tubule opposes the interstitium, and remains nonrandom through stage III of the next cycle. The A(1) spermatogonia of stage VII, derived from most A(pr) and A(al) spermatogonia, and the A(2) spermatogonia of stage IX, derived from the A(1) spermatogonia, are also nonrandomly positioned opposing the interstitium. However, the A(3) population of stage XI becomes randomly distributed around the tubule. To our knowledge, these are the first data to show that the more primitive spermatogonial types (A(s) to A(al)) move to specific sites within the seminiferous tubule. Division of the regularly spaced, more primitive spermatogonia (A(s) to A(al)) leads to the spread of their progeny (A(1) to A(4)) laterally along the base of the seminiferous tubule. The lateral spread from more or less evenly spaced foci ensures that spermatogenesis is conducted uniformly around the entire tubule. The data also suggest that the position of a seminiferous tubule in the mouse is stabilized in relationship to other seminiferous tubules.     

Chronic intermittent but not constant hypoxia decreases NAA/Cr ratios in neonatal mouse hippocampus and thalamus

Chronic constant hypoxia (CCH) and chronic intermittent hypoxia (CIH) are known to have deleterious effects on the central nervous system. Because of the difference in the pattern of hypoxic exposure, it is possible that the pathological outcome would vary. The N-acetyl aspartate/creatine (NAA/Cr) ratio is a reliable marker of neuronal integrity, and this can be noninvasively measured by proton nuclear magnetic resonance spectroscopy. P2 CD1 mouse pups with their dams were exposed to either CCH, where the Fi(O(2)) was maintained at 11% continuously or to CIH, where the Fi(O(2)) was varied between 21 and 11% every 4 min. P30 mice exposed to intermittent hypoxia for 4 wk demonstrated a significant decrease in the NAA/Cr ratio in the hippocampus and thalamus, which was reversed by a subsequent exposure to 4 wk of normoxia. Meanwhile, mice exposed to 4 wk of constant hypoxia did not demonstrate any differences in their NAA/Cr ratios from controls in these brain regions. These results indicate that an intermittent pattern of hypoxic exposure may have a more adverse effect on neuronal function and integrity than a continuous one. The reversal of NAA/Cr levels to baseline during the return to normoxia indicates that therapeutic strategies targeted at alleviating the intermittent hypoxic stress in diseases, such as obstructive sleep apnea, have the potential for inducing significant neurocognitive recovery in these patients.     

Occludin is concentrated at tight junctions of mouse/rat but not human/guinea pig Sertoli cells in testes

Occludin is theonly integral membrane protein identified to date as a component oftight junctions (TJs). Here, we examined the distribution andexpression of occludin in murine testis bearing well-developed TJ. Inthe adult mouse testis, occludin was concentrated at TJ strands, whichare located at the most basal regions of lateral membranes of Sertolicells. In immunoblotting, occludin showed a characteristic multiplebanding pattern, suggesting that occludin is highly phosphorylated inthe testis. In 1-wk-old mouse testis, occludin was distributeddiffusely at the lateral membranes of Sertoli cells, and even at thisstage, highly phosphorylated occludin was detected. With development,occludin gradually became concentrated at the most basal regions ofSertoli cells. The same results were obtained in rat, but unexpectedlyoccludin was not detected in human or guinea pig Sertoli cells byimmunofluorescence microscopy as well as by immunoblotting. Inasmuch asTJs are also well developed in Sertoli cells of these species, weconcluded that, at least in the testes of these species, there are some Sertoli cell-specific isoforms of occludin or other TJ-associated integral membrane proteins that differ from occludin.

     

Comparative study of the teratogenic effects of chlordiazepoxide and diazepam in the fetal hamster

A single, intraperitoneal injection of either chlordiazepoxide (280–3100 mg/kg) or diazepam (120–980 mg/kg) was administered to pregnant hamsters on day 8 of gestation. These dosages produced a dose-dependent sedation of pregnant animals lasting up to 36 hours, and a combined maternal mortality rate of 21% (chlordiazepoxide) and 5% (diazepam). Animals were sacrificed on gestation day 12 and the fetuses were examined for gross malformations. Although there was a dose-related increase in the frequency of malformed fetuses (3.4%–54.7% for chlordiazepoxide, and 0–58.7% for diazepam), the lowest teratogenic dose was noted to be 280 mg/kg, i.e., almost 500 times and 1000 times the average daily recommended therapeutic doses for chlordiazepoxide and diazepam, respectively. The majority of fetal malformations observed with both compounds were either exencephaly or cranioschisis. The results of this study should be interpreted with caution in so far as their relevance to humans is concerned. The terata were observed at exceedingly high doses (700–7000 times the average human use dose), and the malformations noted by us have not been associated with the use of minor tranquilizers in human pregnancy. Also, although we found no gross anomalies in the litters of dams deprived of food and water for up to 72 hours, the confounding role of prolonged periods of sedation and resulting inactivity, and possible hypoxia and hypothermia needs to be explored further.     

Aneuploidy is not induced by ethanol during spermatogenesis in the Chinese hamster

Aneuploidy was scored in spermatogonial stages and at both meiotic divisions in male Chinese hamsters exposed to alcohol in vivo. After light ether anesthetization, the animals were intubated (by gastric tube) with 1.5 ml of 12.5% ethanol, whereas controls were given 1.5 ml of distilled water. Gonadectomy was performed 3.5-24 h after ethanol exposure. Ethanol-dosed animals were obviously intoxicated, as evidenced by a rolling gait; serum alcohol levels in 10 animals that were tested peaked 1-2 h after exposure. Among the animals exposed to ethanol, no significant difference over time in the rates of aneuploidy was observed. These data were pooled, and, when compared to control rates, no significant difference could be attributed to ethanol exposure. The aneuploidy found could therefore be interpreted as background rates, and these compared well with data previously published for the Chinese hamster. Several artifactual phenomena were observed: Up to 15% aneuploid spermatogonial metaphases were seen in test and control animals. These were attributed to the mechanical breaking-up of closely apposed groups of diploid spermatogonia. Significant numbers of artifactual diploid MII figures and hypohaploid MI and MII figures were also recorded. To address the possibility that a spermatogonial or other long-term effect could be detected, two animals (with controls) were dosed with 12.5% ethanol daily for 13 and 16 days before sacrifice. No aneuploidy attributable to ethanol was found at MII in these animals either.     

Mitochondrial respiration of complex II is not lower than that of complex I in mouse skeletal muscle

Skeletal muscle (SKM) requires a large amount of energy, which is produced mainly by mitochondria, for their daily functioning. Of the several mitochondrial complexes, it has been reported that the dysfunction of complex II is associated with several diseases, including myopathy. However, the degree to which complex II contributes to ATP production by mitochondria remains unknown. As complex II is not included in supercomplexes, which are formed to produce ATP efficiently, we hypothesized that complex II-linked respiration was lower than that of complex I. In addition, differences in the characteristics of complex I and II activity suggest that different factors might regulate their function. The isolated mitochondria from gastrocnemius muscle was used for mitochondrial respiration measurement and immunoblotting in male C57BL/6J mice. Student paired t-tests were performed to compare means between two groups. A univariate linear regression model was used to determine the correlation between mitochondrial respiration and proteins. Contrary to our hypothesis, complex II-linked respiration was not significantly less than complex I-linked respiration in SKM mitochondria (complex I vs complex II, 3402 vs 2840 pmol/[s × mg]). Complex I-linked respiration correlated with the amount of complex I incorporated in supercomplexes (r = 0.727, p < 0.05), but not with the total amount of complex I subunits. In contrast, complex II-linked respiration correlated with the total amount of complex II (r = 0.883, p < 0.05), but not with the amount of each complex II subunit. We conclude that both complex I and II play important roles in mitochondrial respiration and that the assembly of both supercomplexes and complex II is essential for the normal functioning of complex I and II in mouse SKM mitochondria.