Active uptake of sodium in the gills of the hyperregulating shore crabCarcinus maenas

Isolated posterior gills of shore crabs,Carcinus maenas, previously acclimated for at least 1 month to brackish water of 10 S, were connected with an artificial hemolymph circulation by means of thin polyethylene tubings. Gills were symmetrically perfused and bathed with 50 % sea water. Transepithelial potential differences (PDs) and fluxes of sodium between medium and blood were measured under control conditions and following reductions of PDs by means of 5 mM internal (blood side) ouabain, 0.5 mM internal and external (bathing medium) NaCN or by exhaustion of energy reserves along with a prolonged perfusion period of more than 9 h. In these experiments²²Na was used as tracer. Each of the three modes of reducing transepithelial potential differences resulted in a decrease in sodium influxes from 500–1000 µmoles g^–1 h^–1 to 250–400 µmoles g^–1 h^–1. The findings suggest that sodium influx, which normally greatly exceeds efflux, was diminished by its active component. The remaining non-inhibitable influx equals efflux values. Our findings thus indicate that efflux is completely passive, while influx has — beside a passive component of efflux magnitudes — an additional active portion which is much larger than the passive component. Since ouabain is a specific inhibitor of the Na-K-ATPase, our results confirm previous findings (Siebers et al., 1985) that the basolaterally located Na-K-ATPase generates the transepithelial potential difference in the gills, which is inside negative by about 6–12 mV. Inhibition of the active portion of sodium influx by internal ouabain along with reduced PDs suggests that transepithelial PDs generated by the branchial sodium pump are the driving force for active sodium uptake in hyperregulating brackish water crabs.     

NaCl absorption across split gill lamellae of hyperregulating crabs: Transport mechanisms and their regulation

The method of mounting split lamellae of crab gills in modified Ussing chambers offers the advantage that active ion transport can be measured as short-circuit current and/or flux of radioactive tracers in relation to the epithelial surface. Moreover, further modern techniques like microelectrode impalements and current-noise analysis can be applied. The epithelium of posterior gills of Chinese crabs (Eriocheir sinensis) acclimated to fresh water actively absorbs Na⁺ and Cl⁻ independent of each other. The epithelium of the gills of shore crabs (Carcinus maenas) acclimated to brackish water actively absorbs NaCl in a coupled mode. The different osmotic gradients maintained by the two crab species are reflected in the characteristics of their gill epithelia. Chinese crabs, migrating to fresh water, have a tight gill epithelium. The gill epithelium of shore crabs, living in brackish water of at least 6–8‰ salinity, is an intermediate between tight and leaky. Regulation of NaCl absorption across the gill epithelium of Chinese crabs is achieved in a hormone-independent way by the haemolymph side osmolarity (autoregulation). Moreover, NaCl absorption is regulated by a hormonal factor of so far unknown chemical nature in the eyestalk extract which stimulates the transport rates via a cAMP-dependent signal transduction pathway, activating apical V-ATPase activity and increasing the number of open apical Na⁺ channels.     

Incorporation of ω6 polyunsaturated fatty acids into phospholipids of the crab Carcinus maenas

The incorporation in vivo of ¹⁴C-18:2 ω6 and ³H-20:4 ω6 fatty acids in phospholipids isolated from gills, hepatopancreas and hemolymph of the crab Carcinus maenas was analysed. PC was the most heavily labelled phospholipid from these ω6-unsaturated fatty acids and appeared to play an important part in the phospholipids metabolism in Crustaceans. The pathway of fatty acids synthesis in phospholipids of C. maenas seems to be similar to those described for mammals. It is at the level of tissue Pl of C. maenas that the renewal of the 20:4 ω6 fatty acid is the most important. It is suggested that the rapid reorganization of phospholipid molecular species composition in the crab is checked by deacylation—reacylation cycle.     

Physiological responses to emersion in the intertidal green crab,Carcinus maenas (L.)

The green shore crab, Carcinus maenas, undergoes on average 6?h periods of emersion during each low-tide cycle during the summer months. Under those conditions, the crab is cut off from its normal water environment and is exposed to potential stress from a suite of environmental and physiological changes: dehydration, compromised gas exchange and resultant internal hypoxia and hypercapnia, thermal stress, and ammonia toxicity. This study examined the comprehensive responses of the green crab in water and to a 6?h emersion period laboratory simulation of a tidal cycle followed by a 1?h re-immersion period, measuring indicators of dehydration, hemolymph osmolality, oxygen uptake, hemolymph acid–base status, heart and ventilatory rate, and hemolymph ammonia and ammonia excretion. Green crabs showed physiological responses of varying magnitude to 6?h of emersion. Individuals were found in the field exclusively under rocks and large clumps of seaweed where temperatures were approximately half those of exposed surfaces and relative humidity was about twice as high as ambient air. During emersion, crabs lost less than 5% of their wet weight, and hemolymph osmolality did not increase significantly. Oxygen uptake continued in air at about 50% of the control, aquatic values; and the gills continued to be ventilated by the scaphognathite, albeit at lower rates. Hemolymph lactate concentrations increased, indicating a shift to a greater reliance on anaerobic metabolism to support energetic needs. A slight acidosis developed in the hemolymph after 1?h of emersion, but it did not increase thereafter. Ammonia concentrations in the hemolymph were unchanged, as ammonia was volatilized by the gills and excreted into the air as NH₃ gas. These results show that the green crab copes with emersion by seeking refuge in microhabitats that mitigate the changes in the physical parameters of intertidal emersion. Physiologically, desiccation is avoided, cardio-respiratory processes are maintained at reduced levels, and hemolymph acid–base balance is minimally affected. Ammonia toxicity appears to be avoided by a shift to excreting NH₃ gas directly or indirectly to air.     

Uptake of cadmium through isolated perfused gills of the Chinese mitten crab, Eriocheir sinensis

Using the perfusion method, we compared cadmium accumulation and influx across the gills of the euryhaline Chinese mitten crab Eriocheir sinensis, exposed to 4.8 microM cadmium in the incubation medium (OUT). Cadmium influx was not observed across posterior gills while it ranged from 0.15 to 6.82 nmol Cd g(-1) gill w.w. h(-1) across anterior ones. For these respiratory gills, a strong increase (40 times) was observed when calcium was removed in both incubation and perfusion media while the lack of sodium in the perfusion medium resulted in a 46 times decrease. For crabs acclimated 15 days to artificial seawater, cadmium influx across anterior gills showed a 21 times decrease when compared with freshwater acclimated ones. On the other hand, after 3 h of perfusion, we detected cadmium accumulation in both types of gills, ranging from 3.8 to 68 nmol Cd g(-1) gill w.w. in anterior gills and from 2.1 to 39 nmol Cd g(-1) gill w.w. in posterior ones. Such accumulations represent between 61.3 and 100% of the total uptake of cadmium through the gills. From these results, we suggest that cadmium can penetrate more easily into the hemolymph space through the 'respiratory' type epithelium present in the anterior gills but absent in the posterior ones. This metal uptake is likely to occur at least in part through the same pathways as calcium. On the contrary, cadmium seems to be sequestered inside the posterior gills, perhaps in the cuticle of the salt-transporting type epithelium.     

The transepithelial potential difference in the gills of the fiddler crab,Uca tangeri: Influence of some inhibitors

Summary Euryhaline Crustacea living in dilute media, counterbalance the salt loss by active absorption of NaCl across the gill epithelium. To investigate the mechanisms involved in salt absorption, transeptithelial potential difference (PD_te) was measured in isolated, perfused gills of the fiddler crab,Uca tangeri. The influence of some specific inhibitors of epithelial ion transport on the PD_te was tested.With symmetrical conditions on both sides of the epithelium, the posterior gills ofUca tangeri showed a spontaneous PD_te of +5 to +10 mV, that is an active transport potential which was positive on the bath side as referred to the hemolymph side. This potential decreased considerably after application of KCN or 2,4-dinitrophenol (DNP) to the perfusion saline.Omission of K⁺ from the perfusion saline or addition of ouabain led to a reversible drop of the PD_te, suggesting that the absorption of Na⁺ and also of Cl^– is driven by the (Na⁺+K⁺)ATPase located in the basolateral membrane of the epithelial cells.Perfusion of the hemolymph space with saline containing diphenylamine-2-carboxylate (DPC) or the loop diuretic furosemide resulted in a decrease of the PD_te.After application of amiloride to the bath saline the PD_te increased. Half-maximum response to amiloride was reached at a concentration of about 10^–5 mol·l^–1. This suggests that one of the Na⁺ pathways across the apical membrane may consist of Na⁺ channels.Abbreviations PD _te transepithelial potential difference - DPC diphenylamine-2-carboxylate - R _ps resistance of perfusate shunt - R _te transepithelial resistance - R _in input resistance - DNP 2,4-dinitrophenol Parts of this study have been reported at the 1st Congress of Comparative Physiology and Biochemistry, Liège 1984, and at the Vth European Colloquium on Renal Physiology, Frankfurt, 1985     

Pathological changes in the nephrocytes of the shore crab, Carcinus maenas, following injection of bacteria

The gills of Carcinus maenas were examined by light and electron microscopy following injection of either sterile saline or the bacteria Bacillus cereus and Moraxella sp., to determine any role(s) for the nephrocytes in the host defense reactions. The results showed that although intact bacteria were not sequestered to the nephrocytes, these cells were active in the removal of large quantities of cell debris from the hemolymph. Much of this material was derived from the breakdown of the hemocytes in response to the presence of bacteria and it's accumulation in the central vacuoles of the nephrocytes resulted in the degradation of these cells. It is proposed that while nephrocytes do not phagocytose intact bacteria, they augment the host defenses by clearing much of the hemocyte and associated bacterial debris from the gills, thus preventing blockage of the lamellar sinuses and subsequent impairment of respiration.     

Biotic resistance experienced by an invasive crustacean in a temperate estuary

Communities high in species diversity tend to be more successful in resisting invaders than those low in species diversity. It has been proposed that the biotic resistance offered by native predators, competitors and disease organisms plays a role. In Yaquina Bay, Oregon, we observed very little overlap in the distribution of the invasive European green crab, Carcinus maenas, and the larger red rock crab, Cancer productus. C. productus dominates the more saline, cooler lower estuary and C. maenas, the less saline, warmer upper estuary. Because caged C. maenas survive well in the lower estuary, we decided to test the hypothesis that C. productus prey on C. maenas and thus contribute to their exclusion from the more physically benign lower estuary. A laboratory species interaction experiment was designed to determine whether C. productus preys on smaller C. maenas at a higher rate than on smaller crabs of their own species. Crabs of both species were collected and sorted by weight into three size classes: small, medium and large. Small and medium crabs of both species were paired with C. maenas and C. productus of various sizes. When conspecifics were paired, mortality was less than 14%, even in the presence of larger crabs. Smaller C. productus survived well in the presence of larger C. maenas, but the reverse was not true. When small C. maenas (60–67 mm carapace width) were matched with medium and large C. productus, their mortality increased to 52% and 76%, respectively. A less dramatic pattern was observed for medium C. maenas (73–80 mm) in the presence of medium and large C. productus. Thus on the West Coast of North America, the more aggressive red rock crab, C. productus, has the potential to reduce the abundance of C. maenas in the more saline and cooler lower estuaries.     

Gill Phospholipids of Mitochondria in Euryhaline Crustaceans as Related to Changes in Environmental Salinity

The distribution of different phospholipids and their variation in fatty acids composition were studied in mitochondrial fractions isolated from anterior and posterior gills of the two euryhaline crabs, Enocheir sinensis and Carcinus maenas, as a function of the environmental salinity. No matter what the salinity, the three more posterior located gills of E. sinensis were shown to contain more unsaturated phospholipids (PE, DPG) and more eicosapentaanoic acids (20:5ω 3) than the three more anterior ones. This was particularly significant when crabs were acclimatized to fresh water. The lipid content of the anterior and posterior gills of the seashore crab C. maenas, on the contrary, showed no significant differences. These results are discussed by taking into consideration the different osmo- and ion-regulation capabilities of the two euryhaline crabs studied and it is proposed that a possible viscotropic regulation might check the activity of membrane-bound enzymes among which the (Na⁺ + K⁺)-ATPase related to the Na⁺-active transport processes involved in maintaining Na⁺ balance.     

Coxal organs of Lithobius forficatus (Myriapoda,Chilopoda)

Summary In Lithobius forficatus each of the coxae of the four posterior trunk segments bear a pore field with several coxal pores. The surrounding single-layered epithelium is composed of four different cell types: the main epithelial cells having a fine-structural organization of transport cells with deep apical and basal folds of the cell surfaces and plasmalemma-mitochondrial complexes, junctional cells, exocrine glands, and the wall cells of the pore channel. The entire epithelium is separated from the hemolymph by an inner cellular sheath. It is assumed that the coxal organs participate in fluid uptake.     

Carbonic anhydrase,a respiratory enzyme in the gills of the shore crabCarcinus maenas

This paper summarizes investigations on the enzyme carbonic anhydrase (CA) in the gills of the osmoregulating shore crabCarcinus maenas. Carbonic anhydrase, an enzyme catalyzing the reversible hydration of CO₂ to HCO₃ ⁻ and H⁺, is localized with highest activities in the posterior salt-transporting gills of the shore crab- and here CA activity is strongly dependent on salinity. Contrary to the earlier hypothesis established for the blue crabCallinectes sapidus that cytoplasmic branchial CA provides the counter ions HCO₃ ⁻ and H⁺ for apical exchange against Na⁺ and Cl⁻, the involvement of CA in NaCl uptake mechanisms can be excluded inCarcinus. Differential and density gradient centrifugations indicate that branchial CA is a predominantly membrane-associated protein. Branchial CA was greatly inhibited by the sulfonamide acetazolamide (AZ) K_i=2.4·10⁻⁸ mol/l). Using the preparation of the isolated perfused gill, application of 10⁻⁴ mol/l AZ resulted in an 80% decrease of CO₂/HCO₃ ⁻ excretion. Thus we conclude that CA is localized in plasma membranes, maintaining the CO₂ gradient by accelerating adjustment of the pH-dependent CO₂/HCO₃ ⁻ equilibrium.     

Measurement of the electrical potential difference across the membrane of the ehrlich mouse ascites tumor cell

The electrical potential difference (PD) across the membrane of the Ehrlich mouse ascites tumor cell has been measured with intracellular microelectrodes. The mean for 111 cells in control Ringer solution was ? 11.2 mV ± 0.29 (SE), interior negative. When sulfate replaced chloride in the external medium the PD fell to ? 2.8 mV if measured as soon as possible after mixing the cells with a sulfate medium, but when nitrate replaced chloride the PD fell only to ? 8.5 mV. Cells equilibrated in nitrate had the same PD as those in control Ringer. These results indicate that the PD is sensitive to changes in the external chloride concentration and that nitrate can substitute for chloride electrically. However, since the PD for chloride, based on the Nernst equation and calculated on the basis of 70% exchangeability of cell chloride, is three times greater than the measured PD, it is hypothesized that sodium contributes significantly to the membrane potential in addition to chloride. On the other hand, potassium does not influence the PD to any great extent.     

Organization of a phyllobranchiate gill from the green shore crab Carcinus maenas (Crustacea,Decapoda)

Summary The phyllobranchiate gills of the green shore crab Carcinus maenas have been examined histologically and ultrastructurally. Each gill lamella is bounded by a chitinous cuticle. The apical surface of the branchial epithelium contacts this cuticle, and a basal lamina segregates the epithelium from an intralamellar hemocoel. In animals acclimated to normal sea water, five epithelial cell types can be identified in the lamellae of the posterior gills: chief cells, striated cells, pillar cells, nephrocytes, and glycocytes. Chief cells are the predominant cells in the branchial epithelium. They are squamous or low cuboidal and likely play a role in respiration. Striated cells, which are probably involved in ionoregulation, are also squamous or low cuboidal. Basal folds of the striated cells contain mitochondria and interdigitate with the bodies and processes of adjacent cells. Pillar cells span the hemocoel to link the proximal and distal sides of a lamella. Nephrocytes are large, spherical cells with voluminous vacuoles. They are rimmed by foot processes or pedicels and frequently associate with the pillar cells. Glycocytes are pleomorphic cells packed with glycogen granules and multigranular rosettes. The glycocytes often mingle with the nephrocytes. Inclusion of the nephrocytes and glycocytes as members of the branchial epithelium is justified by their participation in intercellular junctions and their position internal to the epithelial basal lamina.     

Effects of photoperiod on gluconeogenic activity and total lipid concentration in organs of crabs, Neohelice granulata, challenged by salinity changes

Abstract. This study assessed the effects of long (LD) or short (SD) days on the conversion of [¹⁴C]-glycerol to [¹⁴C]-glucose and total lipid concentration in organs of the crab Neohelice granulata challenged by a change in external salinity. In the 20‰-acclimated crabs, no difference was found in the concentration of total lipids in the muscle, hepatopancreas, gills, or hemolymph between crabs acclimated to SD or LD. In SD crabs, the total lipid levels in the anterior and posterior gills did not decrease during an osmotic challenge. Only in the posterior gills did the total lipid levels decrease during acclimation to the 34‰ medium in LD animals. The total lipid concentration in the hemolymph decreased after 1 d of osmotic stress in SD, and increased in the hepatopancreas. In LD crabs, the lipid contents decreased gradually in muscle, and in the hepatopancreas on day 3 after transfer to 34‰ medium. In 20‰-acclimated crabs, the gluconeogenesis activity in both sets of gills was higher in LD than in SD animals. The gluconeogenesis capacity decreased in both sets of gills on the first day of osmotic challenge in SD, and in the posterior gills on the third day in LD crabs. These results suggest that in organs of N. granulata , photoperiod affects the metabolic adjustments to an osmotic challenge.     

Thermogeography predicts the potential global range of the invasive European green crab (Carcinus maenas)

Aim The highly adaptable estuarine crab (Carcinus maenas) has successfully invaded five temperate geographic regions outside of its native Europe. Here, we determine which environmental factors predict the current distribution of C. maenas and what the potential geographic range of this species might be. We also investigated whether the invasion potential of C. maenas differs with respect to the origin of a native subpopulation. Location Models were developed using global observation records of C. maenas. Methods Boosted regression trees were used to model observations from the (1) native, (2) invasive, (3) southern European, (4) northern European and (5) the combined native and invasive geographic ranges of C. maenas. Results Most established invasions were predicted mainly based on temperature. Interestingly, the environment encountered by established invasions failed to predict the majority of northern European populations; suggesting that invasion potential may differ between distinct native populations. Supporting this suggestion, a model of northern European populations, distinguished from southern European populations based on genetic structure, only predicted established invasions south of Nova Scotia. By contrast, a model of southern European populations predicted most established invasions. Main conclusions These results suggest that invasion potential depends on the European origin of an invasive population and that most invasions have arisen from southern Europe. Finally, a model based on combined native and invasive ranges of C. maenas identified potential geographic range extension along many currently invaded coastlines and the potential invasion of countries like Chile, China, Russia, Namibia and New Zealand.     

Calcium-mobilizing agonists stimulate anion fluxes in cultured endothelial cells from human umbilical vein

Intracellular ion concentrations were determined in split skins of Rana pipiens using the technique of electron microprobe analysis. Based on the 1 min Br uptake from the apical bath, two types of mitochondria-rich (MR) cells could be distinguished: active cells which rapidly exchanged their anions with the apical bath and inactive cells which did not. Br uptake and frequency of active MR cells were closely correlated with the skin conductance, g _t. Replacing Cl in the apical bath with an impermeant anion significantly lowered g _t and the Br uptake and Na concentration of active cells. Even larger reductions were observed after apical amiloride (0.1 mm). The inhibition of the Br uptake was reversible by voltage clamping (100 mV, inside positive). Cl removal and amiloride also led to some shrinkage of active cells. The results suggest that the active cell is responsible for a large part of g _t. Inactive MR cells had much lower Br and Na concentrations which were not significantly affected by Cl removal, amiloride, or voltage clamping. Principal cells, which represent the main cell type of the epithelium, showed only a minimal Br uptake from the apical side which was not correlated with g _t. Moreover, Cl removal had no effect on the Na, Br, and Cl concentrations of principal cells.I wish to thank Cathy Langford for her excellent technical assistance. Financial support was provided by National Institutes of Health grants DK35717 and 1S10-RR0-234501.     

Hemolymph analysis and evaluation of newly formulated media for culture of shrimp cells (Penaeus stylirostris)

Summary Creation of a shirmp cell line has been an elusive goal. This failure may be due to the composition of the cell culture medium, which may be inadequate to support primary cultured cells. Shrimp hemolymph should contain the nutritional components needed to support cell growth and division. We report here the comprehensive biochemical analysis of hemolymph from the blue shrimp,Penaeus stylirostris (Litopenaeus stylirostris) (see Holthuis, L. B. Shrimps, and prawns of the world, in: FAO species catalog. Vol. 1. Rome: Food and Agriculture Organization of the United Nations; 1980), for free amino acids (FAAs), carbohydrates, electrolytes, metals, pH, and osmolality. Levels of hemolymph components were compared to 2×L-15 with 20% fetal bovine serum, a commonly used culture medium for crustacean cells. The FAAs, taurine and proline, and the metals, strontium and zinc, were significantly higher in hemolymph than in the 2×L-15 medium. In contrast, other FAAs were up to 50 times higher in the 2×L-15 medium than in the hemolymph. To mimic more closely the hemolymph composition, we created two new media based on either the 0.2×L-15 or the M199 medium. We compared the microscopic appearance of cells cultured in these media and evaluated deoxyribonucleic acid (DNA) and protein synthesis by³H-thymidine uptake and³⁵S-methionine uptake assays. The ovary cells ofP. stylirostris cultured in either of the new media formed monolayers, while the cells cultured in 2×L-15 medium did not. Despite these differences, there was no evidence of sustained DNA or protein synthesis with any of the media. Future studies to establish a shrimp cell line should focus on analysis of the cell cycle and on overcoming the molecular blocks to cell division.     

Salinity regulates <Emphasis Type="Italic">N</Emphasis>-methylation of phosphatidylethanolamine in euryhaline crustaceans hepatopancreas and exchange of newly-formed phosphatidylcholine with hemolymph

Phosphatidylcholine (PC), the main phospholipid in eukaryotes, is synthesized via two different routes, the phosphatidylethanolamine N-methyl transferase (PEMT) and the CDP-choline pathways. We previously showed in euryhaline fish that salinity impacts the relative contribution of the two pathways for PC biosynthesis, with PEMT pathway being activated in the liver of sea water (SW)-adapted animals. To address the occurrence of such phenomenon in other animals we performed in vivo metabolic studies in two crustacean species: the Chinese crab (Eriocheir sinensis) and the green crab (Carcinus maenas). In both species, the levels of PC and phosphatidylethanolamine in hepatopancreas and hemolymph were not modified by SW-adaptation. In E. sinensis, SW-adaptation activated PC labeling from l-(U-¹⁴C)-serine in the hepatopancreas and resulted in an increased ratio of PC specific activities between hemolymph and hepatopancreas. In C. maenas, incorporation of l-(3-³H)-serine and l-(2-¹⁴C)-ethanolamine into PC of hepatopancreas was strongly inhibited after acclimation to fresh water (FW). The results show that PC synthesis via the PEMT pathway and its subsequent release into hemolymph are both activated in SW- compared to FW-adapted animals. SW-adaptation also resulted in increased tissue concentrations of betaine and labeling from l-(U-¹⁴C)-serine, suggesting that the PEMT-derived PC is used for the synthesis of organic osmolytes. The physiological relevance of these observations is discussed.     

The synthesis of hemolymph proteins by the larval midgut of an insect Calpodes ethlius (Lepidoptera:Hesperiidae)

Ligated tubes of Calpodes ethlius (Lepidoptera:Hesperiidae) larval midgut with normal (i.e. apical secretions into the lumen and basal into the hemocel or medium) or inverted orientation (i.e. apical secretions into the hemocoel or medium and basal into the lumen) were incubated in artificial hemolymph in the presence of [³⁵S]methionine to investigate protein synthesis and vectorial secretion. The midgut synthesizes and secretes at least eight polypeptides basally and seven apically. The tissue also synthesizes many other polypeptides that are not released at either surface. Two dimensional analysis of proteins labeled in vitro and in vivo showed that (a) proteins synthesized in vitro are the same as those synthesized in vivo, (b) different proteins are secreted on apical and basal surfaces, (c) in vitro apical secretions are the same as in vivo luminal proteins, (d) at least two of the basal secretions can be demonstrated in the hemolymph labeled in vivo. Almost all basal secretions showed immunological similarity with hemolymph proteins as observed by immunoprecipitation and fluorography. Arylphorin is a main hemolymph protein synthesized by the midgut. Midgut arylphorin has been identified by its precipitation by antibodies to hemolymph arylphorin. We conclude that insect midgut has bi-directional secretion. Luminal proteins (presumably digestive enzymes and perhaps goblet cell luminal contents) are carried to the apical face. A different set of proteins are carried basally to the hemolymph.