Ammonia excretion and acid-base regulation in the American horseshoe crab, .

Many studies have investigated ammonia excretion and acid-base regulation in aquatic arthropods, yet current knowledge of marine chelicerates is non-existent. In American horseshoe crabs (), book gills bear physiologically distinct regions: dorsal and ventral half-lamellae, a central mitochondria-rich area (CMRA) and peripheral mitochondria-poor areas (PMPAs). In the present study, the CMRA and ventral half-lamella exhibited characteristics important for ammonia excretion and/or acid-base regulation, as supported by high expression levels of Rhesus-protein 1 (LpRh-1), cytoplasmic carbonic anhydrase (CA-2) and hyperpolarization-activated cyclic nucleotide-gated K channel (HCN) compared with the PMPA and dorsal half-lamella.

Fluid absorption in the isolated midgut of adult female yellow fever mosquitoes (Aedes aegypti).

The transepithelial voltage (Vte) and the volume of isolated posterior midguts of adult female yellow fever mosquitoes (Aedes aegypti) were monitored. In all experiments, the initial Vte after filling the midgut was lumen negative, but subsequently became lumen positive at a rate of approximately 1 mV min(-1). Simultaneously, the midgut volume decreased, indicating spontaneous fluid absorption.

Osmoregulation and excretion.

The article discusses advances in osmoregulation and excretion with emphasis on how multicellular animals in different osmotic environments regulate their milieu intérieur. Mechanisms of energy transformations in animal osmoregulation are dealt with in biophysical terms with respect to water and ion exchange across biological membranes and coupling of ion and water fluxes across epithelia. The discussion of functions is based on a comparative approach analyzing mechanisms that have evolved in different taxonomic groups at biochemical, cellular and tissue levels and their integration in maintaining whole body water and ion homeostasis.

Multiple functions of the crustacean gill: osmotic/ionic regulation, acid-base balance, ammonia excretion, and bioaccumulation of toxic metals.

The crustacean gill is a multi-functional organ, and it is the site of a number of physiological processes, including ion transport, which is the basis for hemolymph osmoregulation; acid-base balance; and ammonia excretion. The gill is also the site by which many toxic metals are taken up by aquatic crustaceans, and thus it plays an important role in the toxicology of these species. This review provides a comprehensive overview of the ecology, physiology, biochemistry, and molecular biology of the mechanisms of osmotic and ionic regulation performed by the gill.

Signaling by intracellular Ca2+ and H+ in larval mosquito (Aedes aegypti) midgut epithelium in response to serosal serotonin and lumen pH.

The midgut of larval mosquitoes (Aedes aegypti) mediates a cycle of alkali secretion in the anterior segment (AMG) followed by partial reacidification in the posterior segment (PMG); both processes are serotonin-dependent. Here we report that intracellular Ca(2+)(Ca(i)(2+)) as indicated by Fura-2 fluorescence, is elevated in both tissues in response to serotonin, but the time courses differ characteristically in the two gut segments, and Ca(2+)-free solution abolishes the serotonin response in AMG, but not in PMG, whereas Thapsigargin, an inhibitor of endoplasmic Ca(2+) transport, abolished responsiveness to 5-HT in PMG. These results suggest the origins for the Ca(2+) signal differ between the two tissues.

Serotonin-induced high intracellular pH aids in alkali secretion in the anterior midgut of larval yellow fever mosquito Aedes aegypti L.

The anterior midgut of the larval yellow fever mosquito Aedes aegypti generates a luminal pH in excess of 10 in vivo and similar values are attained by isolated and perfused anterior midgut segments after stimulation with submicromolar serotonin. In the present study we investigated the mechanisms of strong luminal alkalinization using the intracellular fluorescent indicator BCECF-AM. Following stimulation with serotonin, we observed that intracellular pH (pH(i)) of the anterior midgut increased from a mean of 6.

The anterior midgut of larval yellow fever mosquitoes (Aedes aegypti): effects of amino acids, dicarboxylic acids, and glucose on the transepithelial voltage and strong luminal alkalinization.

Isolated anterior midguts of larval Aedes aegypti were bathed in aerated mosquito saline containing serotonin (0.2 micromol L(-1)) and perfused with NaCl (100 mmol L(-1)). The lumen negative transepithelial voltage (V(te)) was measured and luminal alkalinization was determined through the color change of luminal m-cresol purple from yellow to purple after luminal perfusion stops.

Revisiting the cellular mechanisms of strong luminal alkalinization in the anterior midgut of larval mosquitoes.

Here we critically review two recent hypotheses about the mechanism of strong alkalinization by the anterior midgut of mosquito larvae and our tests of these hypotheses. We present experimental evidence against the major components of transport models proposed in these hypotheses. Measurements of the transapical and transbasal proton electrochemical gradients provide an indication of driving forces faced by and generated by the transport mechanisms of the tissue.

Strong alkalinization in the anterior midgut of larval yellow fever mosquitoes (Aedes aegypti): involvement of luminal Na+/K+-ATPase.

Recently, Na(+)/K(+)-ATPase has been detected in the luminal membrane of the anterior midgut of larval yellow fever mosquitoes (Aedes aegypti) with immunohistochemical techniques. In this study, the possible involvement of this ATPase in strong alkalinization was investigated on the level of whole larvae, isolated and perfused midgut preparations and on the molecular level of the Na(+)/K(+)-ATPase protein. Ouabain (5 mM) did not inhibit the capability of intact larval mosquitoes to alkalinize their anterior midgut.

Alkalinization in the isolated and perfused anterior midgut of the larval mosquito, Aedes aegypti.

In the present study, isolated midguts of larval Aedes aegypti L. (Diptera: Culicidae) were mounted on perfusion pipettes and bathed in high buffer mosquito saline. With low buffer perfusion saline, containing m-cresol purple, transepithelial voltage was monitored and luminal alkalinization became visible through color changes of m-cresol purple after perfusion stop.

A structure-function analysis of ion transport in crustacean gills and excretory organs.

Osmotic and ionic regulation in the Crustacea is mostly accomplished by the multifunctional gills, together with the excretory organs. In addition to their role in gas exchange, the gills constitute organs of active, transepithelial, ion transport, an activity of major importance that underlies many essential physiological functions like osmoregulation, calcium homeostasis, ammonium excretion and extracellular pH regulation. This review focuses on structure-function relationships in crustacean gills and excretory effectors, from the organ to molecular levels of organization.

The isolated anterior stomach of larval mosquitoes (Aedes aegypti): voltage-clamp measurements with a tubular epithelium.

The anterior stomach of larval Aedes aegypti was isolated and perfused via two pipettes. For transepithelial voltage (V(te)) measurement, the inflow pipette and the bath were connected via agar bridges to calomel electrodes. For voltage-clamping, the lumen of the tissue contained an Ag/AgCl wire held by the outflow pipette, and the preparation was placed in a bath within a spiral of Ag/AgCl wire.

Adaptation to hypoosmotic challenge in brachyuran crabs: a microanatomical and electrophysiological characterization of the intestinal epithelia.

Besides its role in digestion and nutrient absorption, the crustacean gut participates in osmo/ionic regulation. We investigate microanatomy, ionic permeability and transepithelial electrophysiological parameters in the mid- and hindguts of three hyperosmoregulating crabs that inhabit estuarine waters (Chasmagnathus granulata), brackish mangrove swamp (Sesarma rectum) or freshwater (Dilocarcinus pagei). The abdominal hindguts are cuticle lined, the single-layered epithelia consisting of narrow, columnar cells exhibiting apically dense, unvesiculated cytoplasm.

Ion-motive ATPases and active, transbranchial NaCl uptake in the red freshwater crab, Dilocarcinus pagei (Decapoda, Trichodactylidae).

The present investigation examined the microanatomy and mRNA expression and activity of ion-motive ATPases, in anterior and posterior gills of a South American, true freshwater crab, Dilocarcinus pagei. Like diadromous crabs, the anterior gills of this hololimnetic trichodactylid exhibit a highly attenuated (2-5 microm), symmetrical epithelium on both lamellar surfaces. In sharp contrast, the posterior gill lamellar epithelia are markedly asymmetrical.

Active NaCl absorption across posterior gills of hyperosmoregulating Chasmagnathus granulatus.

Split lamellae of posterior gills of Chasmagnathus granulatus adapted to 2.5 per thousand salinity were mounted in a modified Ussing chamber. With NaCl-saline on both sides of the preparation a transepithelial voltage (V(te)) of 4.

Ion transport across posterior gills of hyperosmoregulating shore crabs (Carcinus maenas): amiloride blocks the cuticular Na(+) conductance and induces current-noise.

Split gill lamellae and gill cuticles of shore crabs (Carcinus maenas) adapted to 10 per thousand salinity were mounted in a modified Ussing-type chamber. With NaCl saline on both sides, split gill lamellae generated a short-circuit current (I(sc)) of -301+/-16 microA cm(-2) at a conductance (G(te)) of 40+/-2 mS cm(-2). The net influxes of Na(+) and Cl(-) were 8.

Hyperosmoregulation in the red freshwater crab Dilocarcinus pagei (Brachyura, Trichodactylidae): structural and functional asymmetries of the posterior gills.

The osmotic and ionic status of the haemolymph and the structural and ion-transport characteristics of the posterior gills of Dilocarcinus pagei, a hololimnetic crab, were investigated. Haemolymph osmolality was 386 +/- 18 mosmol kg(-1), while [Na(+)] and [Cl(-)] were 190 +/- 13 and 206 +/- 12 mmol l(-1), respectively; [K(+)], [Ca(2+)] and [Mg(2+)] were 9.7 +/- 0.