Relating proton pumps with gap junctions: colocalization of ductin,the channel-forming subunit c of V-ATPase,with subunit a and with innexins 2 and 3 during <Emphasis Type="Italic">Drosophila</Emphasis> oogenesis

Background

Ion-transport mechanisms and gap junctions are known to cooperate in creating bioelectric phenomena, like pH gradients, voltage gradients and ion fluxes within single cells, tissues, organs, and whole organisms. Such phenomena have been shown to play regulatory roles in a variety of developmental and regenerative processes. Using Drosophila oogenesis as a model system, we aim at characterizing in detail the mechanisms underlying bioelectric phenomena in order to reveal their regulatory functions. We, therefore, investigated the stage-specific distribution patterns of V-ATPase components in relation to gap-junction proteins.

Results

We analysed the localization of the V-ATPase components ductin (subunit c) and subunit a, and the gap-junction components innexins 2 and 3, especially in polar cells, border cells, stalk cells and centripetally migrating cells. These types of follicle cells had previously been shown to exhibit characteristic patterns of membrane channels as well as membrane potential and intracellular pH. Stage-specifically, ductin and subunit a were found either colocalized or separately enriched in different regions of soma and germ-line cells. While ductin was often more prominent in plasma membranes, subunit a was more prominent in cytoplasmic and nuclear vesicles. Particularly, ductin was enriched in polar cells, stalk cells, and nurse-cell membranes, whereas subunit a was enriched in the cytoplasm of border cells, columnar follicle cells and germ-line cells. Comparably, ductin and both innexins 2 and 3 were either colocalized or separately enriched in different cellular regions. While ductin often showed a continuous membrane distribution, the distribution of both innexins was mostly punctate. Particularly, ductin was enriched in polar cells and stalk cells, whereas innexin 2 was enriched in the oolemma, and innexin 3 in centripetally migrating follicle cells. In lateral follicle-cell membranes, the three proteins were found colocalized as well as separately concentrated in presumed gap-junction plaques.

Conclusions

Our results support the notion of a large variety of gap junctions existing in the Drosophila ovary. Moreover, since ductin is the channel-forming part of a proton pump and, like the innexins, is able to form junctional as well as non-junctional membrane channels, a plethora of cellular functions could be realized by using these proteins. The distribution and activity patterns of such membrane channels are expected to contribute to developmentally important bioelectric signals.

     

Immunolocalization of a proton V-ATPase in ovarian follicles of the tobacco hornworm Manduca sexta

A monoclonal antibody, directed against an H⁺ translocating V-ATPase of the midgut of Manduca sexta, has been used for immunolocalization studies in ovarian follicles and testes of Manduca sexta. In testes, no distinct staining above background levels was observed. In vitellogenic follicles, V-ATPase immunoreactivity first appears in the cytoplasm of the trophocytes and then in the oocyte, but by far the strongest reaction is present in the region of the oolemma during endocytosis. All types of follicle cells surrounding both the oocyte and the trophocyte compartments show a distinct positive reaction. In the cylindrical follicle cells surrounding the oocyte, the immunoreactivity is clearly restricted to the basal part. Our results suggest an important role for V-ATPase in vitellogenin uptake in Manduca, similar to that suggested on electro-physiological grounds in Hyalophora cecropia. © 1995 Wiley-Liss, Inc.     

Ouabain-sensitive H,K-ATPase functions as Na,K-ATPase in apical membranes of rat distal colon

Na,K-ATPase activity has been identified in the apical membrane of rat distal colon, whereas ouabain-sensitive and ouabain-insensitive H,K-ATPase activities are localized solely to apical membranes. This study was designed to determine whether apical membrane Na,K-ATPase represented contamination of basolateral membranes or an alternate mode of H,K-ATPase expression. An antibody directed against the H, K-ATPase alpha subunit (HKcalpha) inhibited apical Na,K-ATPase activity by 92% but did not alter basolateral membrane Na,K-ATPase activity. Two distinct H,K-ATPase isoforms exist; one of which, the ouabain-insensitive HKcalpha, has been cloned. Because dietary sodium depletion markedly increases ouabain-insensitive active potassium absorption and HKcalpha mRNA and protein expression, Na, K-ATPase and H,K-ATPase activities and protein expression were determined in apical membranes from control and sodium-depleted rats. Sodium depletion substantially increased ouabain-insensitive H, K-ATPase activity and HKcalpha protein expression by 109-250% but increased ouabain-sensitive Na,K-ATPase and H,K-ATPase activities by only 30% and 42%, respectively. These studies suggest that apical membrane Na,K-ATPase activity is an alternate mode of ouabain-sensitive H,K-ATPase and does not solely represent basolateral membrane contamination.     

Microscopic and molecular characterization of ovarian follicle atresia in Rhodnius prolixus Stahl under immune challenge

In this work we characterized the degenerative process of ovarian follicles of the bug Rhodnius prolixus challenged with the non-entomopathogenic fungus Aspergillus niger. An injection of A. niger conidia directly into the hemocoel of adult R. prolixus females at the onset of vitellogenesis caused no effect on host lifespan but elicited a net reduction in egg batch size. Direct inspection of ovaries from the mycosed insects revealed that fungal challenge led to atresia of the vitellogenic follicles. Light microscopy and DAPI staining showed follicle shrinkage, ooplasm alteration and disorganization of the monolayer of follicle cells in the atretic follicles. Transmission electron microscopy of thin sections of follicle epithelium also showed nuclei with condensed chromatin, electron dense mitochondria and large autophagic vacuoles. Occurrence of apoptosis of follicle cells in these follicles was visualized by TUNEL labeling. Resorption of the yolk involved an increase in protease activities (aspartyl and cysteinyl proteases) which were associated with precocious acidification of yolk granules and degradation of yolk protein content. The role of follicle atresia in nonspecific host-pathogen associations and the origin of protease activity that led to yolk resorption are discussed.     

Characterization of cation-rich follicle cells in vitellogenic follicles of Drosophila melanogaster

Abstract. Cations in the ovarian follicles of Drosophila were precipitated with potassium antimonate and the distribution of the precipitates in the follicle cells was studied. In three stage 10 follicles, the precipitate density in the different follicle cells was determined by counting the number of precipitates per unit area in an electron microscope. Among the follicle cells, those migrating centripetally between the nurse cells and oocyte were found to differ widely in their precipitate density. When stage 10B follicles at different substages were compared, the number of precipitaterich follicle cells was found to increase with developmental age. At middle and late stage 10B, groups of cation-rich follicle cells extended from the region of the ring canals to the outer face of the follicle. We also found changes in the precipitate density of the border cells during vitellogenesis. The precipitate-rich follicle cells may play a role in the postulated electrical current flow.     

An ion-transporting ATPase encodes multiple apical localization signals

Epithelial cells accumulate distinct populations of membrane proteins at their two plasmalemmal domains. We have examined the molecular signals which specify the differential subcellular distributions of two closely related ion pumps. The Na,K-ATPase is normally restricted to the basolateral membranes of numerous epithelial cell types, whereas the H,K-ATPase is a component of the apical surfaces of the parietal cells of the gastric epithelium. We have expressed full length and chimeric H,K-ATPase/Na,K-ATPase cDNAs in polarized renal proximal tubular epithelial cells (LLC-PK1). We find that both the alpha and beta subunits of the H,K-ATPase encode independent signals that specify apical localization. Furthermore, the H,K-ATPase beta-subunit possesses a sequence which mediates its participation in the endocytic pathway. The interrelationship between epithelial sorting and endocytosis signals suggested by these studies supports the redefinition of apical and basolateral as functional, rather than simply topographic domains.     

Ambient salinity modulates the expression of sodium pumps in branchial mitochondria-rich cells of Mozambique tilapia,Oreochromis mossambicus

Na,K-ATPase (sodium pumps) provide the primitive driving force for ion transport in branchial epithelial cells. Immunoblots of epithelial homogenates of both seawater (SW)- and freshwater (FW)-adapted tilapia gills as well as rat brain homogenate, a positive control, revealed one major band with a molecular weight of about 100 kDa. SW-adapted tilapia gills possessed larger (about 2-fold) amounts of sodium pumps compared with FW-adapted tilapia gills. (3)H-ouabain binding representing functional binding sites of Na,K-ATPase was also higher (about 3.5-fold) in gills of SW-adapted tilapia compared to that of FW-adapted fish. Moreover, specific activities of SW fish were higher (about 2-fold) than those of FW fish. Double labeling of Na,K-ATPase and Con-A, a fluorescent marker of MR cells, in tilapia gills followed by analysis with confocal microscopy showed that sodium pumps were localized mainly in MR cells, including the SW type and different FW types. Although more-active expression of Na,K-ATPase was demonstrated in gills of SW-adapted tilapia, no significant differences in densities of apical openings of MR cells were found between SW- and FW-adapted fish. These results indicate that, during salinity challenge, tilapia develop more "functional" Na,K-ATPase in SW-type MR cells to meet physiological demands.     

Na,K-ATPase inhibition alters tight junction structure and permeability in human retinal pigment epithelial cells

Na,K-ATPase regulates avariety of transport functions in epithelial cells. In cultures ofhuman retinal pigment epithelial (RPE) cells, inhibition of Na,K-ATPaseby ouabain and K⁺ depletion decreased transepithelialelectrical resistance (TER) and increased permeability of tightjunctions to mannitol and inulin. Electrophysiological studiesdemonstrated that the decrease in TER was due to an increase inparacellular shunt conductance. At the light microscopy level, thisincreased permeability was not accompanied by changes in thelocalization of the tight junction proteins ZO-1, occludin, andclaudin-3. At the ultrastructural level, increased tight junctionpermeability correlated with a decrease in tight junction membranecontact points. Decreased tight junction membrane contact points andincreased tight junction permeability were reversible inK⁺-repletion experiments. Confocal microscopy revealed thatin control cells, Na,K-ATPase was localized at both apical andbasolateral plasma membranes. K⁺ depletion resulted in alarge reduction of apical Na,K-ATPase, and after K⁺repletion the apical Na,K-ATPase recovered to control levels. Theseresults suggest a functional link exists between Na,K-ATPase and tightjunction function in human RPE cells.

     

Development of gap junctions in normal and mutant ovaries of Drosophila melanogaster

An ovarian follicle of Drosophila consists of an oocyte, 15 nurse cells, and hundreds of follicular epithelial cells. A freeze-fracture analysis of the surfaces between glutaraldehyde-fixed ovarian cells showed that all three cell types were interconnected by gap junctions. This is the first report of gap junctions between adjacent nurse cells, between nurse cells and oocytes, and between follicle cells and oocytes in Drosophila. Since we did not observe intramembranous particle clumping into crystalline patterns and since structurally different gap junctions occurred at different times in development and at different cell-cell interfaces, it is unlikely that fixation artifacts influenced particle distribution in our experiments. A computer-assisted morphometric analysis showed that the extent, size, and morphology of gap junctions varied with development and that these junctions can cover up to 9% of the cell surfaces. To test the role of gap junctions in follicular maturation, we studied ovaries from flies homozygous for the female sterile mutation fs(2)A17, in which follicles develop normally until yolk deposition commences. During the development of mutant follicles, gap junctions became abnormal before any other morphological aspect of the follicle. These studies show that gap junctions are available to play an important role in coordinating intercellular activities between all three cell types in ovarian follicles of Drosophila.     

Yolk synthesis in ovarian follicles ofDrosophila

Summary The autonomous synthesis of yolk proteins in ovarian follicles ofDrosophila melanogaster was analyzed. Vitellogenic follicles were labelled with³⁵S-methionine in vitro and the newly synthesized yolk proteins were separated by SDS-polyacrylamide gel electrophoresis. Possible contamination of the follicle preparations caused by adhering fat body cells could be excluded by culturing follicles in males prior to labelling in vitro. When labelled follicles were cut at the nurse cell/oocyte border the three yolk proteins (YP1, YP2, YP3) were found only in posterior fragments containing ooplasm and follicle cells, whereas two radioactive protein bands (A and B) were detected in nurse cells (anterior fragments). The yolk proteins of these five bands were characterized by peptide mapping. Band A protein, migrating a little more slowly than YP2, is closely related to both YP1 and YP2 while band B contains a yolk protein which is very similar to YP3. Hence, the nurse cells have been identified as a site of vitellogenin synthesis within the ovary ofDrosophila.Supported by the Deutsche Forschungsgemeinschaft, SFB 46     

Ultrastructural observations of previtellogenic ovarian follicles of dove

Dove ovarian follicle is a complex structure composed of oocyte surrounded by a somatic compartment consisting of theca externa, theca interna and granulosa. The structure of ovarian follicle (1 and 2 mm) of dove was studied by electron microscopy. The granulosa was pseudostratified in the 1-mm-diameter follicles and stratified with two or three irregular rows of cells in the 2-mm-diameter follicles. In the larger follicle indentations between oocyte and granulosa cells become more numerous and the microvilli of granulosa cell elongated to form a zona radiata with similarly elongated oocyte microvilli. Lining bodies were present at the tips of granulosa microvilli and in the cortical region of the oocyte. In the oocyte cortex were observed coated pits, coated vesicles, dense tubules, multivesicular bodies and primordial yolk spheres. Primordial yolk spheres may contain lining bodies and were observed fused with dense tubules and multivesicular bodies or associated with smooth cisternae.     

Exclusion of plasma lipoproteins of intestinal origin from avian egg yolk because of their size

Increasing the fat content of the diet increases the proportion of large triglyceride-rich (TGR) lipoproteins (portomicrons) in laying-hen plasma, but has no effect on the size distribution of yolk TGR-lipoproteins. Electromicrographs of the ovarian follicle walls of hens fed a high-fat diet show the presence of numerous portomicron-like particles in the lumen of the thecal capillaries, in the pericapillary spaces and in the theca interna, but portomicrons were absent from the basal lamina, between the granulosa cells and in newly deposited yolk. Most of the lipoprotein lipase activity in the ovarian follicles is associated with the granulosa cells, but total activity in the follicle is very small compared to heart or adipose tissue. The results indicate that the ovarian follicle of the laying-hen specifically excludes lipoproteins of intestinal origin from yolk, most probably because they are too large to pass through the connective tissue matrix of the basal lamina. The low lipoprotein lipase activity of the ovarian follicle, together with its distribution within the follicle wall, indicates that the ovarian follicles make little contribution to catabolism of circulating portomicrons.     

Factors promoting vitellogenic competence and yolk deposition in the cockroach ovary: The post-ecdysis female

Incorporation of labelled histidine into a follicle cell product was shown to be juvenile hormone-dependent in Periplaneta americana. After 30 min the labelling was localized in the follicle cell cytoplasm, followed by labelling of intercellular spaces between the follicle cells after 60 min, and finally labelling of cortical yolk spheres after 120 min. Synthesis of the follicle cell product was observed exclusively in ovarian follicles participating in yolk formation. DNA synthesis was observed in follicle cell nuclei of ovarian follicles from the early stages of follicle differentiation to chorion formation. The evidence indicates that, although ovarian follicles exhibit protein synthetic responses to juvenile hormone in adult females, incorporation of thymidine into follicular nuclei suggests that changes in the cell cycle after adult ecdysis do not necessarily affect sensitivity to juvenile hormone.     

Hierarchy of mechanisms involved in generating Na/K-ATPase polarity in MDCK epithelial cells

We have studied mechanisms involved in generating a polarized distribution of Na/K-ATPase in the basal-lateral membrane of two clones of MDCK II cells. Both clones exhibit polarized distributions of marker proteins of the apical and basal-lateral membranes, including Na/K- ATPase, at steady state. Newly synthesized Na/K-ATPase, however, is delivered from the Golgi complex to both apical and basal-lateral membranes of one clone (II/J), and to the basal-lateral membrane of the other clone (II/G); Na/K-ATPase is selectively retained in the basal- lateral membrane resulting in the generation of complete cell surface polarity in both clones. Another basal-lateral membrane protein, E- cadherin, is sorted to the basal-lateral membrane in both MDCK clones, demonstrating that there is not a general sorting defect for basal- lateral membrane proteins in clone II/J cells. A glycosyl- phosphatidylinositol (GPI)-anchored protein (GP-2) and a glycosphingolipid (glucosylceramide, GlcCer) are preferentially transported to the apical membrane in clone II/G cells, but, in clone II/J cells, GP-2 and GlcCer are delivered equally to both apical and basal-lateral membranes, similar to Na/K-ATPase. To examine this apparent inter-relationship between sorting of GlcCer, GP-2 and Na/K- ATPase, sphingolipid synthesis was inhibited in clone II/G cells with the fungal metabolite, Fumonisin B1 (FB1). In the presence of FB1, GP-2 and Na/K-ATPase are delivered to both apical and basal-lateral membranes, similar to clone II/J cells; FB1 had no effect on sorting of E-cadherin to the basal-lateral membrane of II/G cells. Addition of exogenous ceramide, to circumvent the FB1 block, restored GP-2 and Na/K- ATPase sorting to the apical and basal-lateral membranes, respectively. These results show that the generation of complete cell surface polarity of Na/K-ATPase involves a hierarchy of sorting mechanisms in the Golgi complex and plasma membrane, and that Na/K-ATPase sorting in the Golgi complex of MDCK cells may be regulated by exclusion from an apical pathway(s). These results also provide new insights into sorting pathways for other apical and basal-lateral membrane proteins.     

Differential sorting of constitutively co-secreted proteins in the ovarian follicle cells of Drosophila

Conventional and freeze-fracture electron microscopy, immuno-electron microscopy of ovarian cryosections and confocal immunofluorescence were used to analyze the ovarian distribution of the major protein classes being secreted by the follicle cells during the vitellogenic and choriogenic stages of Drosophila oogenesis. Our results clearly demonstrated that at vitellogenic stages the follicle cells co-secrete constitutively vitelline membrane and yolk proteins that are either sorted into distinct secretory vesicles or they are segregated in different parts of bipartite vesicles by differential condensation. Following their exocytosis only the vitelline membrane proteins are incorporated into the forming vitelline membrane. The yolk proteins (along with their hemolymph circulating counterparts) diffuse through gaps amongst the incomplete vitelline membrane and are internalized through endocytosis by the oocyte where they are finally stored into modified lysosomes referred to as alpha-yolk granules. The unexpected immunolocalization of vitelline membrane antigens in the associated body of the alpha-yolk granules may indicate that this structure is a transient repository for the proteins being internalized into the oocyte along with the yolk proteins. In the early choriogenic follicle cells the vitelline membrane and early chorion proteins were found to be co-secreted and to be evenly intermixed into the same secretory vesicles. These findings illuminate new details concerning the follicle cells secretory and oocyte endocytic pathways and provide for the first time evidence for condensation-mediated sorting of constitutively secreted proteins in Drosophila.     

The rôle of juvenile hormone in housefly ovarian follicle morphogenesis

Oögenesis in the housefly, Musca domestica, was divided into a series of 10 stages where stage 1 was the germarium, stage 4 was the beginning of yolk deposition, stage 7 was characterized by maximal nurse cell development, stage 9 by the degeneration of the nurse cells and chorion formation, and stage 10 was the mature egg. It required 69 hr from eclosion at 27°C to develop mature eggs. This represented an oöcyte volume increase of 3700-fold, a seventeenfold increase in follicle length, and a sevenfold increase in weight. The application of 2 μg of isopropyl (E,E)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate (ZR-515) to allatectomized (-CA) flies stimulated egg development, which progressed at the same rate as the controls. The -CA flies did not develop eggs past stage 4, which represented a cessation of development at a volume of 1·4 per cent that of a mature egg and an ovarian dry weight of 11 per cent that of a mature ovary. The follicle cells from -CA flies did not differentiate into the squamous condition over the nurse chamber, did not become columnar over the oöcyte, did not produce the chorion or vitelline membrane, and did not decrease in number as they did on the stage 10 follicles. Endomitosis in the nurse cell nuclei of -CA flies stopped development at 290 c, but maximum development of 2400 c occurred in stage 7 follicles from controls, and then the nurse cells began to disintegrate.     

Immunolocalization of zona pellucida antigens in the ovarian follicle of dogs, cats, horses and elephants

A comparative evaluation of the location of immunoreactive porcine zona pellucida (pZP) glycoproteins was performed with polyclonal rabbit anti-pZP antibodies on ovarian sections of the dog, cat, horse, and elephant. For this, formalin (light microscopy) and glutaraldehyde (transmission electron microscopy [TEM]) fixed ovarian sections were incubated with antibodies raised against highly purified pZP. Staining patterns were determined with diaminobenzidine (DAB) at the light level. The dog ZP had a distinct staining distribution that is characterized by intense staining around the periphery of the ZP and the oolemma and less dense staining throughout the width of the ZP. In dog follicles that contained multiple oocytes, there were oocytes of identical and dissimilar stages. Cat ovarian sections showed uniform staining of the ZP. Horse results showed uniform staining of ZP and ooplasm, and granulosa cells (GC). Elephant sections showed staining of the ZP with dense staining at the oolemma, as well as staining of the ooplasm. In all species the staining of the ZP was not evident until GC differentiation. In all cases there was no staining of ovarian tissue with control normal rabbit serum. Specific staining patterns of ZP were evaluated by TEM and immunogold staining. The immunogold-linked anti-pZP antibodies stained the ZP matrix in all species. There was staining of ooplasm organelles suggesting that ZP secretion originates from the oocyte of the dog and cat. In addition, follicular and ZP measurements were taken that allowed accurate characterization of follicle stage. These findings suggest that in all four species the ZP is recognized by anti-pZP antibodies and there is also evidence to suggest the possible origins of ZP glycoproteins.     

Morphology and ultrastructure of the adult ovarian cycle in Mithracidae (Crustacea,Decapoda, Brachyura,Majoidea)

The ultrastructure of the ovary during development and yolk production is poorly known in Brachyura and Majoidea in particular. Here, we describe the histology, histochemistry and ultrastructure of the adult ovarian cycle in four Mithracidae species from three different genera: Mithrax hispidus, Mithrax tortugae, Mithraculus forceps and Omalacantha bicornuta. All species showed a similar pattern of ovarian development and vitellogenesis. Macroscopically, we detected three stages of ovarian development: rudimentary (RUD), developing (DE) and mature (MAT); however, in histological and ultrastructural analyses, we identified four stages of development. The oocytes of the RUD stage, during endogenous vitellogenesis, have basophilic cytoplasm filled with dilated rough endoplasmic reticulum. The reticulum lumen showed many granular to electron-dense materials among the different stages of development. The Golgi complexes were only observed in the RUD stage and are responsible for releasing vesicles that merge to the endogenous or immature yolk vesicles. At the early DE stage, the oolemma showed many coated and endocytic vesicles at the cortex. The endocytic vesicles merge with the endogenous yolk to form the exogenous or mature yolk vesicles, always surrounded by a membrane, characterizing exogenous vitellogenesis. The exogenous yolk vesicles comprise glycoproteins, showing only neutral polysaccharides. At the late DE stage, endocytosis still occurs, but the amount of endogenous yolk decreases while the exogenous yolk increases. The late DE stage is characterized by the beginning of chorion production among the microvilli. The MAT stage is similar to the late DE, but the endogenous yolk is restricted to a few cytoplasmic areas, the ooplasma is filled with exogenous yolk, and the oolemma has very few coated vesicles. In the MAT stage, the chorion is fully formed and shows two electron-dense layers. The ovarian development of the species studied has many similarities with the very little known Majoidea in terms of the composition, arrangement and increment of the yolk vesicles during oocyte maturation. The main differences are in the vitellogenesis process, where immature yolk formation occurs without the direct participation of the mitochondria but with the participation of the rough endoplasmic reticulum in the endogenous phase.     

Primordial follicle activation and follicular development in the juvenile rabbit ovary

Of all the stages of mammalian folliculogenesis, the primordial to primary follicle transition is the least understood. In order to gain new insights into this process, we have conducted a comprehensive morphological, morphometric and molecular study of ovarian organisation and early follicle development in the rabbit. The structure of ovaries collected from rabbits aged from 2–12 weeks (a period encompassing primordial follicle formation, activation and the first wave of folliculogenesis in this species) has been analysed by light microscopy and the follicles present have been measured and scored for their developmental stage. To establish useful molecular markers of activation, we have further classified follicles according to their expression of the proliferative marker, proliferating cell nuclear antigen, and the zona pellucida protein, ZPB. The activation of primordial follicles is initiated immediately following their formation in the rabbit ovary and is characterised by oocyte growth, granulosa cell morphogenesis and increased granulosa cell mitosis. Enhanced ZPB protein expression at the oolemma is also associated with follicle activation and development. Few primordial follicles in the juvenile rabbit ovary are lost by atresia, as assessed by the TUNEL assay. The appearance of apoptotic granulosa cells is however coincident with the development of antral follicles. This study thus describes the temporal and spatial regulation of early follicular development in the post-natal rabbit ovary and, for the first time, shows that the primordial to primary transition in the juvenile rabbit is a highly ordered process occurring within quantifiable parameters.K.J.H. was supported by the Pest Animal Control CRC and Post Graduate scholarships from the Australian National University.     

Changes in the Na, K-ATPase of neuronal membranes in penicillin-induced epileptic foci in the cerebral cortex of the rat]

The relationship between electrophysiological changes and Na, K-ATPase activity of neuronal membranes in sodium penicillin-induced epileptic foci was studied. Na,K-ATPase activity is inhibited both in the primary focus and in homotopic contralateral area during latent period and in the stage of forming epileptic activity. In the stage of marked convulsive activity Na, K-ATPase is inhibited only in the primary focus. It is shown that penicillin at a concentration range of 2 x 10(-6)--2 x 10(-3) M does not influence Na,K-ATPase activity of crude synaptosomes of the rat brain cortex. It is suggested that Na,K-ATPase inactivation may serve as a pathogenetic factor in the development of convulsive process.