Differential coupling of dopaminergic D2 receptors expressed in different cell types. Stimulation of phosphatidylinositol 4,5-bisphosphate hydrolysis in LtK- fibroblasts, hyperpolarization, and cytosolic-free Ca2+ concentration decrease in GH4C1 cells

Dopaminergic D2 receptors are widely regarded as typical inhibitory receptors, as they both inhibit adenylyl cyclase and decrease the cytosolic free Ca2+ concentration ([Ca2+]i) by activating K+ channels. A D2 receptor has recently been cloned (Bunzow, J. R., Van Tol, H. H. M., Grandy, D. K., Albert, P., Salon, J., Christie, M. D., Machida, C. A., Neve, K. A., and Civelli, O. (1988) Nature 336, 783-787) and expressed in two different cell lines, pituitary GH4C1 cells and Ltk- fibroblasts, where it has been shown to induce inhibition of adenylyl cyclase. We have investigated the additional effector systems coupled to this receptor. The responses observed in the two cells lines, which express similar levels of receptors (0.5-1 x 10(5)/cell), were surprisingly different. In GH4C1 cells D2 receptors failed to affect phosphoinositide hydrolysis and induced a decrease of [Ca2+]i. This latter effect appears to be mediated by hyperpolarization, most likely due to the activation of K+ channels. In striking contrast, in Ltk- fibroblasts the D2 receptor induced a rapid stimulation of inositol(1,4,5)-trisphosphate (+73% at 15 s) followed by the other inositol phosphates, and an immediate increase of [Ca2+]i due to both Ca2+ mobilization from internal stores and influx from the extracellular medium. In both GH4C1 and Ltk- cells, the D2 receptor response was mediated by G protein(s) sensitive to pertussis toxin. The increases of inositol trisphosphate and [Ca2+]i observed in Ltk- cells required dopamine concentrations only slightly higher than those inhibiting adenylyl cyclase (EG50 = 25, 29, and 11 nM, respectively) and were comparable in magnitude to the responses induced by the endogenous stimulatory receptor agonists, thrombin and ATP. The results demonstrate that in certain cells D2 receptors are efficiently coupled to the stimulation of phosphoinositide hydrolysis. The nature of receptor responses appears therefore to depend on the specific properties not only of the receptor molecule but also of the cell type in which it is expressed.     

Mast cell-lysosomal cationic protein interaction: effects of metabolic inhibitors and decay of activated cells on enhanced fluorescence of anilinonaphthalene sulfonate

It has been shown earlier that the interactions of the isolated rat peritoneal mast cells with cationic protein from rabbit neutrophil lysosomes (band 2 protein) can be studied using anilinonaphthalene sulfonate (ANS) as a fluorescent probe. In the present communication, binding of ANS dye to the mast cells interacting of histamine release by metabolic inhibitors was found to have no effect on enhancement of ANS fluorescence. On the other hand, inhibition of histamine release at high concentration of Ca2+ (14.4 mM) was accompanied by the decrease in enhance fluorescence. In the presence of 7.2 mM of Sr2+, the release of histamine was enhanced with small but significant increase in ANS fluorescence. The cells heated to 42 degrees C partially lost their capacity to release histamine without the loss of enhanced fluorescence. The mast cells interacting with B2 at 10 degrees C for various time intervals showed time-dependent loss in histamine releasing capacity with concomitant loss in enhanced fluorescence. These studies suggest that the enhancement of ANS fluorescence is associated with the early events of the cell membrane caused by interaction of B2 with the cells. The extracellular cations significantly influence this early event.     

ULTRASTRUCTURE OF OOSPORE GERMINATION IN PYTHIUM APHANIDERMATUM

Transmission electron microscopy was used in an examination of dormant and germinating oospores of Pythium aphanidermatum (Edson) Fitzp. Predominant cytoplasmic components of the dormant oospore were a single, centrally located globule and numerous storage bodies surrounding the globule. The lipid nature of the central globule and storage bodies was indicated by the examination of Br₂-treated and untreated, fixed specimens. Three layers of the oospore wall were distinguished. During the early stages of oospore germination, the central globule developed incurvatures and became partially surrounded by vacuoles. The thick middle layer of the wall showed a change in staining properties and became thin in the region of germ tube emergence. Germlings incubated on corn meal agar differed substantially from those incubated in nutrient broth during the later stages of germination. The role of vacuoles and vesicles in the utilization of storage reserves during germination is discussed.     

Aerobic and anaerobic metabolism during activity in snakes

Summary Oxygen consumption and blood lactate concentration in the snakesColuber constrictor, Crotalus viridis, Lichanura roseofusca andMasticophis flagellum and whole body lactate concentration inCrotalus viridis andMasticophis flagellum were determined under standard conditions and after a bout of maximal activity induced by a 5 min period of mechanical stimulation. Observations were made atT _b=35°C inColuber, Crotalus, andMasticophis and 32°C inLichanura. Maximal oxygen consumption inColuber andMasticophis was twice that ofCrotalus and 4 x that ofLichanura (Fig. 1). Post-active whole body lactate concentration inMasticophis was twice that ofCrotalus (Fig. 2). Immediately post-active and 30 min post-active blood lactate concentration inColuber andMasticophis was 1.5 x and 3.5 x that ofCrotalus andLichanura, respectively (Fig. 3). These data support conclusions that: (a) maximal energy production by these snakes correlates well with their respective modes of predation and defense, the highly active predatorsColuber andMasticophis being capable of the greatest net energy production during activity; (b)Coluber andMasticophis exhibit aerobic scopes as high or higher than any other comparably sized reptile heretofore investigated; (c) weight specific anaerobic metabolism probably does not decrease with increasing body size in reptiles; (d) anaerobic metabolism provides >50% of net energy production during five minutes of activity in all species examined (Table 1).     

Hydrolysis of cyclosporin A: Identification of 1,11 seco-cyclosporin A and 4,5 secoisoCyclosporin A by FAB-MS/MS

We have previously reported that treatment of CsA with aqueous HCl gives rise to the formation of a number of water-soluble compounds. Two of these were identified from their FAB-MS/MS spectra as open-chain nona- and decapeptides. We describe here the identification of two other main compounds deriving from the same treatment. Identification was rendered possible from the comparison of their FAB-MS/MS spectra with those of methyl and acetyl derivatives. The two compounds are water-soluble, open-chain undecapeptides corresponding to 1,11 seco-CsA and of 4,5 seco-isoCsA, respectively.     

Bakers' yeast uridine nucleosidase is a regulatory copper containing protein.

The enzymatic properties of homogeneous bakers' yeast uridine nucleosidase, prepared as previously described (G. Magni et al., J. Biol. Chem. 1975 $\text{250}$, 9–13) have been further investigated, and in addition to glucose-6-phosphate and ribose the enzyme activity was inhibited by ribose-5-phosphate and ribulose-5-phosphate. The curves describing this inhibitions were sigmoidal and when the data were plotted according to Hill, n′ values different from 1 were observed suggesting the existence of interactions among the inhibitory molecules binding sites. Furthermore the percentage of inhibition exerted by glucose-6-phosphate, ribose and ribose-5-phosphate on the enzyme activity varied at different pH values. The addition of various chelating agents to the activity assay mixture caused a strong inhibition of the enzyme activity and metal analysis by atomic absorption spectrophotometry, colorimetric methods and electronic paramagnetic resonance, indicated the presence of 1 copper atom per enzyme molecule. Finally the inhibition exerted by metal ions on the enzyme activity was described.     

Winds at departure shape seasonal patterns of nocturnal bird migration over the North Sea

On their migratory journeys, terrestrial birds can come across large inhospitable areas with limited opportunities to rest and refuel. Flight over these areas poses a risk especially when wind conditions en route are adverse, in which case inhospitable areas can act as an ecological barrier for terrestrial migrants. Thus, within the east-Atlantic flyway, the North Sea can function as an ecological barrier. The main aim of this study was to shed light on seasonal patterns of bird migration in the southern North Sea and determine whether departure decisions on nights of intense migration were related to increased wind assistance. We measured migration characteristics with a radar that was located 18 km off the NW Dutch coast and used simulation models to infer potential departure locations of birds on nights with intense nocturnal bird migration. We calculated headings, track directions, airspeeds, groundspeeds on weak and intense migration nights in both seasons and compared speeds between seasons. Moreover, we tested if departure decisions on intense migration nights were associated with supportive winds. Our results reveal that on the intense migration nights in spring, the mean heading was towards E, and birds departed predominantly from the UK. On intense migration nights in autumn, the majority of birds departed from Denmark, Germany and north of the Netherlands with the mean heading towards SW. Prevailing winds from WSW at departure were supportive of a direct crossing of the North Sea in spring. However, in autumn winds were generally not supportive, which is why many birds exploited positive wind assistance which occurred on intense migration nights. This implies that the seasonal wind regimes over the North Sea alter its migratory dynamics which is reflected in headings, timing and intensity of migration.     

Follicular growth and sex steroids in adult females of the endemic Amazonian freshwater stingray Potamotrygon wallacei (Chondrichthyes,Potamotrygonidae)

Environmental Biology of Fishes - This study evaluated how the plasma steroid hormones testosterone (T) and 17β-estradiol (E2) are related to follicular development in regenerating females of...     

Coarser taxonomic resolutions are informative in revealing fish community abundance trends for the world’s warmest coral reefs

Coral Reefs - The Arabian Gulf is a natural laboratory to examine how subtropical coral reef ecosystems might change in responding to recurring heating events because of uniquely high water...