Steady-state current flow through gap junctions. Effects on intracellular ion concentrations and fluid movement.

Double voltage clamp studies were performed on gap junctions contained in septal membranes of the earthworm median giant axon. The gap junctions exhibited no conductance changes in response to voltages imposed across either the septal membrane or the plasma membrane. However, the trans-septal current displayed a slow (10 s) relaxation in response to transjunctional voltage steps. The experimental evidence suggests that this relaxation is a polarization of the septum due to local accumulation/depletion of permeant ions. A theoretical analysis of this observation suggests that the applied electric field causes accumulation of impermeant anions on one side of the junction and depletion on the other, which leads to a change in concentration of permeant ions to maintain macroscopic electroneutrality. The change in concentration of permeant ions generates a transjunctional equilibrium potential that opposes junctional current flow. These results indicate that currents flowing through gap junctions can have an influence on the distribution of intracellular ions. Moreover, the theoretical analysis suggests that such currents will be accompanied by significant intracellular and intercellular water flow.     

Observations on the seasonal and yearly occurrence and the distribution ofAtyaephyra desmaresti (Millet, 1831) (Crustacea,Decapoda, Natantia) in The Netherlands

Summary The seasonal occurrence ofAtyaephyra desmaresti in The Netherlands has been studied by sampling the cooling-water filtering screens of power stations situated along the rivers Rhine and Meuse. The shrimps were only found in large numbers at the two power stations with vegetation in the cooling-water intake areas. Fluctuations in the seasonal occurrence showed great similarity for these two localities. Highest numbers of shrimps were impinged in November. High numbers also occurred in September, while a lower peak in numbers was found in May.Changes in the numbers of records during the last 30 years in The Netherlands were compared with climatological fluctuations (severe or mild winters), indicating that this mainly southern-European species is living here at the limits of its ecological and geographical range.The distribution in The Netherlands reveals thatAtyaephyra desmaresti mainly occurs in freshwater habitats, although it tolerates higher chlorinities.     

Chromosomes of Syrphidae

In this report the karyotypes of 54 species of the tribe Milesiini and of four species of the tribe Myoleptini are described in detail with illustrations and idiograms. These species belong in the genera Lejota, Myolepta, Blera, Calliprobola, Criorhina, Hadromyia, Milesia, Somula, Sphecomyia, Spilomyia, Syritta, Temnostoma, Tropidia and Xylota. Six species have 2n = 8 chromosomes, 35 have 2n = 10 (including Xylota nemorum which has about 20 extra microchromosomes in some specimens), 15 have 2n = 12, one has 2n = 14, and Somula decora has 2n = 10 large chromosomes plus about eight microchromosomes. The mean total complement length (TCL) for 347 complements analysed in these tribes was 53.7 but there is great variation between TCL's of complements analysed even from a single fly. Karyotypes of species of Myolepta in the Myoleptini resemble in certain respects those of species of Tropidia in the Milesiini. Our observations support Currran's transfer of Lejota cyanea to the Milesiini. The 2n = 12 karyotypes of species of Blera, Criorhina, Lejota, Milesia, and to a lesser extent Sphecomyia, have some features in common. Spilomyia species have rather distinct 2n = 10 karyotypes. Certain species in Calliprobola, Syritta and Hadromyia are karyologically similar to some species of the genus Xylota in which species studied fall into fairly distinct karyological groups. These observations provide clear evidence of the accumulation of karyotypic variations in the origin of species in these two tribes.     

Notes on chromosome behaviour in the spermatogenesis of the damselflyEnallagma cyathigerum (Charp.) (Odonata: Coenagrionidae)

The chromosome number in the damselflyEnallagma cyathigerum (Charp.) is 2n =27, 2n =28, n =14 (13). The sex determining mechanism is XX-XO, the X segregates postreductionally in the male.     

Biosynthesis of phosphatidylinositol glycan-anchored membrane proteins. Design of a simple protein substrate to characterize the enzyme that cleaves the COOH-terminal signal peptide

Many nascent proteins that are destined to be anchored to plasma membranes by a phosphatidylinositol glycan (PI-G) are in the range of 50-70 kDa so that changes of 2-3 kDa between precursors and products during processing are not easily detected. Furthermore, PI-G-anchored proteins are generally glycosylated so that changes between the nascent (prepro) proteins and the mature products are not due simply to the loss of signal peptides. These problems have made it difficult to monitor the processing of the prepro form of wild type human placental alkaline phosphatase (PLAP) in a cell-free system. We have designed a smaller and simpler substrate of PI-G "transamidase" derived by deletion of approximately 60% of the internal sequence of preproPLAP 513. This engineered protein, preprominiPLAP 208, retains the NH2- and COOH-terminal signal peptides of PLAP as well as all the epitopes for site-directed antibodies of the latter, but is devoid of glycosylation sites, the active site, and most of the cysteine residues. With preprominiPLAP, it has been possible to demonstrate, in a cell-free system, step by step conversion to the pro form and then to the mature form, with the concomitant loss of the appropriate signal peptides. These changes were shown to be time- and enzyme concentration-dependent. Studies with Asp-179 site-directed mutants of preprominiPLAP showed the same specificity for amino acids with a monosubstituted beta carbon at the cleavage/attachment site that were found previously with wild type PLAP.     

Identification of pristanoyl-CoA oxidase as a distinct, clofibrate non-inducible enzyme in rat liver peroxisomes.

In this paper we describe the identification of pristanoyl-CoA oxidase activity in rat liver peroxisomes. This activity was not stimulated by clofibrate feeding. Furthermore, the activity was found in multiple tissues. These results show that pristanoyl-CoA oxidase is different from any of the known oxidases which include a clofibrate-inducible acyl-CoA oxidase and the recently identified cholestanoyl-CoA oxidase. Gelfiltration and chromatofocusing experiments provide conclusive evidence that we are dealing with a novel acyl-CoA oxidase with a unique function in peroxisomal beta-oxidation.