Freeze-tolerance adaptations,including haemolymph protein and lipoprotein nucleators,in the larvae of the cranefly Tipula trivittata

The terrestrial overwintering larvae of the cranefly Tipula trivittata were freeze tolerant (able to survive the freezing of their extracellular body fluids) throughout the winter and spring of 1982–1983 until they pupated in mid-May. The larvae were most cold tolerant (24 h lower lethal temperatures of ?25 to ?30°C) in late January and early February. Sorbitol, at a maximal concentration of ～0.4 M, was the only polyol determined to be present at high levels and sorbitol accounted for most of the seasonal fluctuation in osmotic concentration. Haemolymph inorganic ion (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?) concentrations did not vary seasonally.The supercooling points of the larvae remained constant at ?6 to ?7°C over the study period because of the presence of haemolymph ice nucleating factors. These ice nucleating factors consist not only of haemolymph proteins, as had been demonstrated previously in other insect species, but also lipoproteins.     

Effects of starvation and dehydration on ionic balance in Schistocerca gregaria

This study describes the effects that prolonged dehydration has on ionic balance in Schistocerca gregaria. When adult locusts are dehydrated for 7 days the body weight reduces by 10–20% and the haemolymph volume by 35–50%, but haemolymph concentrations of Na⁺, K⁺ and Cl⁻ change only slightly. On dehydration Na⁺ and Cl⁻ are removed from the haemolymph; 25% of the removed ions is excreted and 75% is evenly distributed in the body of the locust. The amount of potassium excreted always exceeds that removed from the haemolymph. Mature adults control more effectively than young ones the haemolymph ionic composition during dehydration, but young adults show a smaller reduction in haemolymph volume. In the normal state of hydration, 76% of the total body Na⁺ and 56% of the total body Cl⁻ is present in the haemolymph. These fall to 62 and 42% respectively on dehydration and increase to 77 and 50% on rehydration.     

Stimulated fluid secretion is sodium dependent in the Malpighian tubules of Locusta migratoria

The ionic dependencies of stimulated and unstimulated Locusta tubules have been studied. K⁺, Na⁺, Cl^? are essential to both basal and stimulated secretion. K⁺ is secreted against a concentration gradient in unstimulated tubules. In response to diuretic hormone or cAMP application, there is a dramatic influx of K⁺ into the lumen. A high level of Na⁺ and Cl^? in the bathing medium is required to allow maximal fluid secretion. The tubules show an apparent impermeability to Na⁺; its concentration in the secreted fluid is always much less than in the bathing medium. If Na⁺ is omitted from the medium and excess K⁺ added (80 mM K), then although basal secretion occurs (2.5 nl/min), the tubules fail to respond to stimulation. Clearly Na⁺ has an important indirect role to play in stimulated fluid secretion.     

Hydromineral regulation in the saline water corixid Trichocorixa reticulata (Hemiptera: Corixidae)

The aquatic corixid Trichocorixa reticulata (Guerin-Meneville) inhabits coastal marshes, brackish water ponds and salt ponds of high salinity, suggesting the presence of well developed mechanisms for hydromineral regulation.Groups of corixids acclimated in salinities ranging from fresh water to just above 300% sea water (100‰) were analyzed for total body water content, haemolymph ionic and osmotic levels, and haemolymph free amino acids.Results indicate an excellent ability to maintain haemolymph Na⁺, Cl^?, Mg²⁺ and K⁺ hyperosmotic to the medium at low salinities and hyposmotic at high salinities. Calcium appears to conform closely to changes in external medium, becoming hyposmotic at very high salinities (80‰).Total haemolymph osmotic pressure was well regulated, the freezing point depression varying from 0.75°C in distilled water to 1.15°C in salinities of 100‰. Total body water was maintained at approx. 75% of the total animal wet weight at all salinities tested.Free amino acids were maintained between 40–60 mM in all tests and did not appear to change with salinity.     

Urine composition and kidney function in the pulmonate freshwater snail Lymnaea stagnalis

• 1.1. Final urine is intermittently released from the pneumostome of the pulmonate freshwater snail Lymnaea slagnalis. A technique is described to sample this fluid.
• 2.2. The ionic composition of final urine greatly differs from that of haemolymph; Na⁺ and Cl⁻ are reabsorbed to a considerable degree. In lettuce fed snails K⁺ is excreted.
• 3.3. The urine Na⁺ and Cl⁻ concentrations are about 38 and 31 mM lower, respectively, than the haemolymph concentrations, also when the latter concentrations vary.

     

Cl− transport in apical plasma membrane vesicles isolated from bovine tracheal epithelium

The Cl^? transport properties of the luminal border of bovine tracheal epithelium have been investigated using a highly purified preparation of apical plasma membrane vesicles. Transport of Cl^? into an intravesicular space was demonstrated by (1) a linear inverse correlation between Cl^? uptake and medium osmolarity and (2) complete release of accumulated Cl^? by treatment with detergent. The rate of Cl^? uptake was highly temperature-sensitive and was enhanced by exchange diffusion, providing evidence for a carrier-mediated transport mechanism. Transport of Cl^? was not affected by the ‘loop’ diuretic bumetanide or by the stilbene-derivative anion-exchange inhibitors SITS (4-acetamido-4′-isothiocyanostilbene-2,2′-disulfonic acid) and DIDS (4,4′-diisothiocyanostilbene-2,2′-disulfonic acid). In the presence of the impermeant cation, tetramethylammonium (TMA⁺), uptake of Cl^? was minimal; transport was stimulated equally by the substitution of either K⁺ or Na⁺ for TMA⁺. Valinomycin in the presence of K⁺ enhanced further Cl^? uptake, while amiloride reduced Na⁺-stimulated Cl^? uptake towards the minimal level observed with TMA⁺. These results suggest the following conclusions: (1) the tracheal vesicle membrane has a finite permeability to both Na⁺ and K⁺; (2) the membrane permeability to the medium counterion determines the rate of Cl^? uptake; (3) Cl^? transport is not specifically coupled with either Na⁺ or K⁺; and, finally (4) Cl^? crosses the tracheal luminal membrane via an electrogenic transport mechanism.     

Sexual and seasonal variations in osmoregulation and ionoregulation in the estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda)

The estuarine crab Chasmagnathus granulatus (Crustacea, Decapoda, Brachyura) inhabits salt marshes along the South Atlantic coast from Rio de Janeiro (Brazil) to Patagonia (Argentina). In the present study, salinity tolerance (0-45‰; 16-1325 mOsm/kg H₂O) and hemolymph osmotic and ionic (Na⁺, Cl⁻, and K⁺) regulation in both female and male C. granulatus were analyzed in summer and winter. Results showed that both female and male C. granulatus are euryhaline. Mortality was only observed in extremely low salinity (0‰; 16 mOsm/kg H₂O) for both sexes. For females, the LT₅₀ at 0‰ salinity was similar in summer (20.1 h) and winter (17.4 h). Males were more tolerant to salinity than females in both seasons, and mortality was observed only in summer (LT₅₀ = 50.9 h). Results from freshly collected crabs or long-term (16-day) osmotic and ionic regulation experiments in the laboratory showed that male C. granulatus is a better hyper-osmoregulator than female in summer and winter. However, a hypo-osmoregulatory ability was only observed in females experimentally subjected to salinity 40‰ (1176 ± 11 mOsm/kg H₂O) in both seasons. In both sexes, hyper-osmotic regulation was achieved by hyper-regulating hemolymph Na⁺, Cl⁻, and K⁺ concentration. In females, hypo-osmotic regulation was achieved by hypo-regulating hemolymph Na⁺ and Cl⁻ concentration. Long-term (16-day) osmotic and ionic regulations in different salinities were similar in males or females collected and tested in summer and winter. Despite this lack of a seasonal effect on hemolymph osmoregulatory and ionoregulatory patterns in males or females, a marked seasonal difference in the dynamics of these processes was observed for both sexes. In the first 2 days after hypo-osmotic shock (20‰→5‰; 636→185 mOsm/kg H₂O), variations in female osmolality and ion (Na⁺ and Cl⁻) concentration were larger and faster in winter than in summer, while in males the opposite was observed. Furthermore, a seasonal effect on the crab response to hyper-osmotic shock (20‰→40‰; 636→1176 mOsm/kg H₂O) was only observed in males. A new osmolality and ion (Na⁺ and Cl⁻) concentration steady state was faster achieved in winter than in summer. Regarding sexual differences, females showed a better capacity to hypo-regulate the hemolymph osmolality and Na⁺ concentration than males, even after a sudden increase in salinity (hyper-osmotic shock) in both seasons. On the other hand, males showed a better capacity to hyper-regulate the hemolymph osmolality and Na⁺ concentration than females, even after a sudden decrease in salinity (hypo-osmotic shock), especially in winter. Taken together, results reported in the present study suggest the need to consider both sex and collection season as important factors in future osmotic and ionic regulation studies in estuarine crabs.     

Osmotic acclimation of the brackish water xanthophyceae,Vaucheria dichotoma (L.) MARTIUS: Inorganic ion composition and amino acids

The salinity tolerance ofVaucheria dichotoma, a siphonous Xanthophycean alga was investigated. The alga survived an external osmotic potential range between 74 and 1, 176 mOsmol (ca. 2.5 and 40.0 ppt. (parts per thousand]). Turgor pressure was regulated in salinities ranging from 74 to 441 mOsmol. With further increase of the salinity, turgor pressure decreased from 153 to 9 mOsmol (0.44 to 0.08 MPa). At 441 mOsmol salinity the major intracellular ions were present in the following concentrations (mM/l cell water): K⁺, 145; Na⁺; 90; sulphate, 91; Cl⁻, 91. Under the most severe salinity stress (1,176 mOsmol) the ionic concentration increased to (mM/l cell water): K⁺, 250; Na⁺, 75; sulphate, 35; Cl⁻, 351. The content of amino acids: alanine (Ala), threonine (Thr and glutamic acid (Glu) was lower, nerver exceeding 5–11 mM, however; the concentrations were positively correlated with salinity.     

The salinity tolerance of the invasive golden apple snail (Pomacea canaliculata)

We exposed snails of an invasive species of golden apple snail (Pomacea canaliculata) to five artificial sea water treatments at salinity levels of 0, 5, 10, 15 or 20 parts per thousand (ppt) to assess their salinity tolerance. We observed the behaviour, heart rate, total haemocyte counts, haemolymph ionic concentration and Na⁺/K⁺-ATPase activity in the mantle at 0, 12, 24, 48, 72 and 96 h post salinity exposures. The heart rate declined with increasing salinity, while Na⁺/K⁺-ATPase activity in the mantle presented a reverse trend, possibly to maintain normal osmolality. A trend of rising total haemocyte count was observed from 0 ppt and 5 ppt to 10 ppt salinities, while a sudden increase in the count was observed at 15 ppt and 20 ppt salinity groups. Furthermore, haemolymph Cl^?, Na⁺ and K⁺ concentrations increased directly with elevated salinity. An additional trial was performed to assess the growth performance of the snails under exposure to low salinities. During a 1 month trial, snails grew better at 5 ppt salinity treatment. Taken together, our results demonstrate that P. canaliculata can tolerate salt stress to some extent. The finding also obviously implies a possible invasive risk to estuaries.     

Fluxes and compartmentation of K+, Na+ and Cl−, and action of auxins in suspension-cultured Petroselinum cells

Transport of ⁸⁶Rb⁺/K⁺, ²²Na⁺, ³⁶Cl^?, and [³H]indole acetic acid (IAA) has been studied on suspension-cultured cells of the parsley, Petroselinum crispum (Mill) Nym. By compartmental analysis two intracellular compartments of K⁺, Na⁺, and Cl^? have been identified and ascribed to the cytoplasm and vacuole; half-times of exchange were around 200 s and 5 h, respectively. According to the Ussing-Teorell flux equation, active transport is required for the influx into the cytoplasm at the plasmalemma (K⁺, Cl^?) and the tonoplast (K⁺, Na⁺, Cl^?). The plasmalemma permeability pattern, P_K:P_Na:P_Cl=1.00:0.24:0.38, features an increased chloride permeability compared with cells from higher plant tissues. IAA uptake showed an exponential timecourse, was half-maximal after 10 min, and a linear function of the IAA concentration from 10^?9 to 10^?5 M. IAA and 2,4-dichlorophenoxy acetic acid reduce the apparent influx of K⁺, Na⁺, Cl^? during the initial 30 min after addition and subsequently accelerate both in- and efflux of these ions. We discuss that auxins could affect the ion fluxes in a complex way, e.g. by protonophorous activity and by control of the hypothetical proton pump.     

Specific drug sensitive transport pathways for chloride and potassium ions in steady-state ehrlich mouse ascites tumor cells

A major aim of this investigation was to determine whether, in steady-state ascites cells, Cl^? transport can be partitioned into a furosemide-sensitive cotransport with K⁺ and a separate 4,4′-isothiocyanostilbene-2,2′-disulfonic acid (DIDS) sensitive self-exchange. Both Cl^? and K⁺ fluxes were studied. The furosemide- and Cl^? sensitive K⁺ fluxes were equivalent, both in normal ionic media and when the external K⁺ concentration, [K⁺]_o, was varied from 4 to 30 mM. The stoichiometry of the furosemide-sensitive Cl^? and K⁺ fluxes was 2 Cl^?: 1 K⁺ at 0.1 and 0.5 mM drug levels but increased to 3 Cl^? : 1 K⁺ at 1.0 mM furosemide. DIDS at 0.1 mM had no effect on the K⁺ exchange rate but inhibited Cl^? exchange by $\text{39\% ± 2}$ (S.E.). The effects of DIDS and 0.5 mM furosemide on Cl^? transport were additive but 1.0 mM furosemide and DIDS had overlapping inhibitory actions. Thus furosemide acts on components of K⁺ and Cl^? transport which are linked to each other, but the drug also inhibits an additional DIDS-sensitive Cl^? pathway, when present at higher concentrations. The dependence of the furosemide-sensitive K⁺ and Cl^? transport on [K⁺]_o was also studied; both fluxes fell as the [K⁺]_o increased. The latter results recall those in an earlier study by Hempling (Hempling, H.G. (1962) J. Cell. Comp. Physiol. 60, 181–198).     

The ascidian sperm reaction: evidence for Cl- and HCO3- involvement in acid release

Ascidia callosa sperm are triggered to undergo initiation of the sperm reaction (mitochondrial swelling) by increasing the pH or lowering the Na⁺ concentration of the medium. The optimal [Na⁺] for acid release is 20 mM with excellent correlation between acid release and initiation of morphological changes. Increasing the [K⁺] to around 20 mM inhibits acid release when applied up to 1 min after triggering the sperm but with less inhibition at 2 and 4 min, suggesting that K⁺ inhibits initiation of acid release rather than acid release itself. Acid release and the sperm reaction can also be triggered by Cl^?-free (NO^?₃ or glutamate substituted) seawater (SW). Cl^? efflux accompanies H⁺ efflux with twice as many Cl^? being released as H⁺. Both H⁺ and Cl^? release in Cl^?-free SW are dependent upon CO₂ being present in HCO^?₃-free medium, suggesting that H⁺ efflux is in part Cl^? and HCO^?₃-mediated. However, the chloride channel blocking agent SITS has no effect on H⁺ release and augments Cl^? release. Acid release results in a substantial increase in internal pH as determined by partitioning of 9-amino acridine. We envision acid release from ascidian sperm as involving two systems, the Na⁺-dependent acidification system of unreacted sperm and the Cl^?- and HCO^?₃-mediated H⁺ release at activation. The mechanism controlling acid release would then involve inactivation of the internal acidification process and activation of the chloride-bicarbonate-mediated alkalinization process.     

Influence of ouabain on Na+ and K+ concentration in haemolymph of Drosophila hydei and appearance of Malpighian tubules

After injection of ouabain into the body cavity, the Malpighian tubules of Drosophila larvae show a characteristic appearance which differs from the normal. The primary urine, which is mainly found in particles, is diluted and the concretions are washed away through the proximal part of the tubule and the ureter into the hindgut. In the haemolymph the Na⁺ and K⁺ concentrations change significantly. The K⁺ concentration increases rapidly to double the normal, while later the Na⁺ concentration rises up to 2·3 times the normal. Water movements are not the cause of the concentration changes because the quotient $\text{Na}\text{K}$ varies widely. Thus primary ion regulation mechanisms are influenced in the insect body by application of g-strophanthin. This is evidence for the existence of a ouabain-sensitive ATPase, which is decisively involved in the ion transport mechanisms in the insect body.     

Vasoconstriction triggered by hydrogen sulfide: Evidence for Na+,K+,2Cl-cotransport and L-type Ca2+ channel-mediated pathway

ObjectivesThis study examined the dose-dependent actions of hydrogen sulfide donor sodium hydrosulphide (NaHS) on isometric contractions and ion transport in rat aorta smooth muscle cells (SMC).MethodsIsometric contraction was measured in ring aortas segments from male Wistar rats. Activity of Na⁺/K⁺-pump and Na⁺,K⁺,2Cl^-cotransport was measured in cultured endothelial and smooth muscle cells from the rat aorta as ouabain-sensitive and ouabain-resistant, bumetanide-sensitive components of the ⁸⁶Rb influx, respectively.ResultsNaHS exhibited the bimodal action on contractions triggered by modest depolarization ([K⁺]_o=30 mM). At 10^?4 M, NaHS augmented contractions of intact and endothelium-denuded strips by ~ 15% and 25%, respectively, whereas at concentration of 10^?3 M it decreased contractile responses by more than two-fold. Contractions evoked by 10^?4 M NaHS were completely abolished by bumetanide, a potent inhibitor of Na⁺,K⁺,2Cl^-cotransport, whereas the inhibition seen at 10^?3 M NaHS was suppressed in the presence of K⁺ channel blocker TEA. In cultured SMC, 5×10^?5 M NaHS increased Na⁺,K⁺,2Cl^- - cotransport without any effect on the activity of this carrier in endothelial cells. In depolarized SMC, ⁴⁵Ca influx was enhanced in the presence of 10^?4 M NaHS and suppressed under elevation of [NaHS] up to 10^?3 M. ⁴⁵Ca influx triggered by 10^?4 M NaHS was abolished by bumetanide and L-type Ca²⁺ channel blocker nicardipine.ConclusionsOur results strongly suggest that contractions of rat aortic rings triggered by low doses of NaHS are mediated by activation of Na⁺,K⁺,2Cl^-cotransport and Ca²⁺ influx via L-type channels.     

The Nature of the In Vivo Sodium and Chloride Uptake Mechanisms through the Epithelium of the Chilean Frog Calyptocephalella gayi (Dum. et Bibr., 1841) : Exchanges of hydrogen against sodium and of bicarbonate against chloride

The Chilean frog, Calyptocephallela gayi, placed in dilute NaCl solutions may pump Na⁺ and Cl^- at very different rates depending on the kind of bath solutions in which it was preadapted. Furthermore, Na⁺ and Cl^- may be absorbed from solutions in which the accompanying coion, such as sulfate and choline, respectively, is impermeant. In all these cases it is obligatory to postulate the existence of two ionic exchange mechanisms, Cl^- and Na⁺, being exchanged against endogenous anions and cations, respectively. It has been determined that Na⁺ is exchanged against endogenous H⁺ and that Cl^- is exchanged against HCO₃^-. In animals pumping Na⁺ and Cl^- from dilute NaCl solutions Na⁺ or Cl^- uptake may be selectively inhibited, while the flux of the accompanying ion remains unchanged. This is considered to be an additional proof that both Na⁺ and Cl^- fluxes are always independent. The role of the ionic exchange mechanisms in the direct regulation of the Na⁺ and Cl^- levels in the internal medium is discussed as well as their relationship in the regulation of the acid-base equilibrium; other physioecological considerations have been treated.     

The Na+,K+,2Cl−-cotransport system in HeLa cells: Aspects of its physiological regulation

We have previously reported on the biochemical properties of a Na⁺,K⁺,2Cl^?-cotransport in HeLa cells and here we deal with aspects of its physiological regulation. Na⁺,K⁺,2Cl^?-cotransport in HeLa cells was studied by ⁸⁶Rb⁺ influx and ⁸⁶Rb⁺/²²Na⁺ efflux measurements. The effects of rat atrial natriuretic peptide (ANP), isoproterenol, and amino acids on ⁸⁶Rb⁺ flux, mediated by the bumet-anide-sensitive Na⁺, K⁺, 2Cl^?-cotransport system and the ouabain-sensitive Na⁺/K⁺-pump, were investigated. ANP reduced bumetanide-sensitive ⁸⁶Rb⁺ influx under isotonic as well as under hypertonic conditions. Similar decrease of bumetanide-sensitive ⁸⁶Rb⁺ influx was observed in the presence of 8-bromo-cGMP, while neither isoproterenol as a β-receptor agonist nor 8-bromo-cAMP-could alter bumetanide-sensitive ⁸⁶Rb⁺ influx. Furthermore, efflux of ⁸⁶Rb⁺ and ²²Na⁺ was greatly reduced in the presence of bumetanide and ANP. Together with our recent findings, showing functionally active, high affinity receptors for ANP on HeLa cells (Kort and Koch, Biochim. Biophys. Res. Commun. 168:148–154, 1990), this study indicates that ANP participates in the regulation of the Na⁺, K⁺, 2Cl^?-cotransport system in HeLa cells. Further measurements revealed that amino acids as present in the growth medium (Joklik's minimal essential medium) and the amino acid derivative α-methyl-aminoisobutyric acid (metAlB, 1 and 5 mM, respectively) also reduced Na⁺, K⁺, 2Cl^?-cotransport-mediated ⁸⁶Rb⁺ uptake and diminished the stimulatory effect of hypertonicity on the cotransporter. In addition, the Na⁺/K⁺-pump was markedly stimulated in the presence of amino acids, while neither ANP and 8-Br-cGMP nor isoproterenol and 8-Br-cAMP had a significant effect on the activity of the Na⁺/K⁺-pump.     

The influence of aerial exposure upon respiratory and osmotic properties of haemolymph from two intertidal mussels, Mytilus edulis L. and Modiolus modiolus L.

pH and P_O2, in Mytilus edulis L. and Modiolus modiolus L. decrease, while P_CO2 and the concentrations of Ca²⁺ and Cl^? increase during air exposure. The increase in the concentration of Ca²⁺ is 10 times greater than that of Cl^?. There is a linear correlation between the concentration of Ca²⁺ and the haemolymph P_CO2.The significance of shell valve movements and of the $\text{Ca}{}^{\mathrm{2+}}\text{H}{}^{\mathrm{+}}$ buffering by the CaCO₃ shell in response to air exposure is discussed.     

The Na+, K+, and Cl- Content of Goose Salt Gland Slices and the Effects of Acetylcholine and Ouabain

In goose salt gland slices incubated in bicarbonate-buffered medium which contained 170 mEq of Na⁺/liter, net total tissue Na⁺, expressed as milliequivalents per kilogram, was, in the presence of either acetylcholine (plus eserine) or ouabain, significantly higher than that of the bathing fluid. Acetylcholine caused an increase in the tissue Na⁺ content as compared with untreated slices; there was an approximately equivalent decrease in K⁺ and a significant decrease in Cl^-. The calculated net intracellular concentrations of Na⁺, expressed as milliequivalents per liter of intracellular water, in unstimulated, acetylcholine-stimulated, and ouabain-treated slices were 2.1, 3.1, and 2.7 times higher, respectively, than the concentration of Na⁺ in the bathing fluid. The net intracellular concentration of Na⁺, expressed as milliequivalents per liter of intracellular water, in slices incubated in the presence of acetylcholine was 531 mEq/liter; this is approximately the same as the concentration of Na⁺ in the secreted fluid of the goose salt gland (515 mEq/liter). The results indicate that the main concentration gradient for Na⁺ could be established across the basal membrane. The data do not indicate whether this involves active transport of Na⁺ per se. A second stage which might involve Na-K ATPase activity at the luminal membrane is discussed. The sum of the total tissue Na⁺ and K⁺ was approximately 250 mEq/kg, whereas the Cl^- content was only approximately 130 mEq/kg.     

Inorganic ions in spermathecal fluid and their transport across the spermathecal membrane of the queen bee, Apis mellifera

Micropuncture and microanalytical methods were employed to investigate the rôle of the spermathecal epithelium of the honey queen-bee in providing the appropriate conditions for the prolonged storage of spermatozoa. It was found that the epithelium maintains large concentration gradients of inorganic ions, generates an electrical potential difference of 21 mV, lumen positive, and produces a pH difference of up to 2.4 pH units between spermathecal fluid (SF) and haemolymph (H). The $\text{SF}\text{H}$ concentration ratios for K⁺, Na⁺, Ca⁺⁺, Cl^?1, HPO₄^??, H₂PO₄^? and amino acids were 7.7; 0.5; 0.8; 0.4; 1.03; 0.004; 0.3, respectively. While the pH value of haemolymph was constant at 6.17, the pH of SF increased with age from 7.3 to 8.6 over the first 3 days. The calculated electrochemical potential differences suggest that the epithelium of the spermathecal wall secretes K⁺ (and possibly HCO₃^? or OH^?) actively into the lumen, but handles Na⁺ passively. This pattern conforms with the organization of ion transport in other insects.     

Sodium balance in the catfish Clarias mossambicus exposed to acid water

African catfish, Clarias mossambicus showed no ill effects when kept in acid water pH 4–5 for 3–4 days. Their ionic regulatory response was examined and during 24 h exposure to water of pH 4, Na⁺ efflux increased significantly but was not matched by an increase in Na⁺ influx resulting in a substantial net loss of body Na⁺, which was reduced from 65.4 mmol · kg^?1 to 35.6 mmol · kg^?1, with smaller losses of Cl^? and K⁺.