Thomas H. Dietz

BODY FLUID COMPOSITION AND AERIAL OXYGEN CONSUMPTION IN THE FRESHWATER MUSSEL, LIGUMIA SUBROSTRATA (SAY): EFFECTS OF DEHYDRATION AND ANOXIC STRESS

1. Ligumia subrostrata, removed from water will survive >40 days if dehydration is minimized by high relative humidity. They are not anoxic but consume oxygen from the air (Qo2 59 µl O2/g dry tissue-hr). One source of energy is from the large glycogen stores (36% of dry tissue).2. Animals removed from water and exposed to either low relative humidity (45-55%) or N2 atmosphere will survive about 5-7days. The maximum total solute in the body fluids of surviving animals is 160-180 mOsmoles.3. Sodium, Cl, K, and Ca account for 72% of the total solute in the body fluids of fresh water acclimated animals. Dehydration increases the concentration of Na proportional to the amount of water lost. There is a significant shift of Cl from the tissues into the body fluids during dehydration.4. When the animals are out of water, forced anoxia increases the body fluid total solute but the Na and Cl contribution is small. The major ions in the body fluids are calcium and bicarbonate or succinate; reflecting a build up of m...

Osmotic and ionic regulation in Lumbricus terrestris L.

1. Earthworms maintain a hyperionic steady state while living in a dilute solution containing Na+, K+, Ca+2, Cl- and HCO3-(PW).2. The inside (coelomic fluid) of worms is electronegative by 12 to 30 mV relative to the bath (PW).3. Sodium and chloride are transported across the skin against an electrochemical gradient. Each ion may be transported independently of the other presumably in exchange for an endogenous ion of like charge.4. For animals in PW, Cl- is exchanged at a rate of 0.9 µeq/10g-hr and Na+ at a rate of 0.3 µeq/10g-hr. The influx of Na+ is dependent on Na+ concentration in the bath and displays saturation kinetics (Vmax= 1 µeq/10 g-hr; Ks = 1.3 mMoles/l). Chloride kinetics were not analyzed.5. Salt depletion increases the influx of Na+ and C1- causing a net uptake of each ion.6. Inulin and dextran are cleared from the coelomic fluid of PW-adapted worms at a rate of 75 µl/10 g-hr. Excretion of these compounds is probably through nephridia so that this is a maximum estimate of the rate of urine...

Osmoregulation in Dreissena polymorpha: the Importance of Na, Cl, K, and Particularly Mg

Zebra mussels (Dreissena polymorpha) are unusual in that they cannot survive in Mg-deficient water. Analysis of blood samples from mussels obtained in the field indicated a Mg concentration of 1.5-2.0 mM immediately after animal collection. However, Mg concentration in the blood decreased rapidly when the mussels were transferred to Mg-free artificial pondwater (PW); the t1/2 was 24 h. Blood Mg decreased to the limits of detection within 2 weeks, and the time to 50% mortality was about 17 days in Mg-free PW. When Mg-depleted specimens of D. polymorpha were returned to PW containing Mg, the net flux was 3 μmol Mg (g dry tissue.h)-1, and blood Mg concentration was restored within a day to 0.4-0.6 mM. Mussels depleted of Mg did not survive beyond 51 days. When mussels were acclimated to K-free pondwater (containing Mg), their osmoregulatory ability was impaired, and the total solute of the blood dropped from 30-36 to 21-24 mosm, with blood Na and Cl concentrations declining 30-50%. This ion-depleted condition was reversed within 45 h upon return of K to the pondwater bathing medium. D. polymorpha individuals were unable to survive beyond 5 days in deionized water and required minimal concentrations of Na, Cl, K, and Mg for prolonged storage (>51 days) under laboratory conditions. Mussels survived Ca-deficient solutions for more than 51 days, presumably because they were able to mobilize Ca from internal stores (shell) to maintain blood calcium at 1 mM.

Mucociliary Transport in Living Tissue: The Two-Layer Model Confirmed in The Mussel Mytilus edulis L

The present study combined video confocal laser microscopy (1) and tissue reflectance and autofluorescence to visualize mucus position and mucociliary transport in excised living gill tissue from the blue mussel Mytilus edulis. Rafts of mucus and embedded particles were transported atop a periciliary space traversed by frontal cilia, which engaged the mucus layer and moved it during the effective stroke, disengaging and completing the cycle during the recovery stroke. These results confirm the two-layer model for mucociliary transport in the mussel gill. Given the conservative nature of ciliated epithelial structure and function (2, 3), and the structural similarity of mucociliary surfaces as diverse as terrestrial vertebrate respiratory epithelium and molluscan gill, the two-layer mechanism of mucociliary transport may be a general feature of Metazoan biology.

The role of latero-frontal cirri in particle capture by the gills of Mytilus edulis

In this study we examined the mechanism of particle capture in Mytilus edulis, using radioactive-label clearance studies, progressive fixation, and scanning electron microscopy to visualize in detail the cirri and their range of motion. Confocal laser scanning microscopy was used to observe the interaction of cirri with 1 mucrom fluorescent latex particles on live strips of control and serotonin-treated isolated gill tissue. The gills of M. edulis possess large, complex latero-frontal cirri composed of 18-26 pairs of cilia. Particles that were intercepted by the cirri were transferred to the water current on the frontal surface of the filament where they were propelled toward the ventral particle groove. Clearance studies demonstrated that M. edulis removed Escherichia coli from 5 degrees C seawater bathing medium at 4.9 ml g(-1) dry tissue min(-1). When the gills were exposed to 10(-3) M serotonin, the latero-frontal cirri stopped moving and became fixed in a flexed position that partially blocked the frontal surface of the filament. Clearance studies demonstrated that removal of E. coli from the seawater bathing medium was reduced 90% to 0.5 ml g(-1) dry tissue min(-1) when 10(-3) M serotonin was present. These data demonstrated that for small particles (< 2 microm) in the near field, movement of cirri was essential for successful capture either by direct contact or with water acting as a hydromechanical coupler.

Musculature Associated with the Water Canals in Freshwater Mussels and Response to Monoamines In Vitro

The gills of freshwater mussels perform many functions that depend on water flow through the water canals and channels. Regulation of water flow depends in part on ciliary activity and in part on the contraction of musculature underlying the gill filament and water channel epithelium. Obliquely striated muscles control water canal openings (ostia) at the base of the filaments and also at the entry into the water channel (internal ostia, IO). The muscles adjacent to the ostia are oriented in an anterior-posterior direction (perpendicular to gill filaments), and those controlling the internal ostia are oriented in a dorso-ventral direction (parallel to gill filaments). Small bundles of fibers radiate from the major dorso-ventral IO muscle bands and appear to insert at the base of the water canal epithelial cells at the canal-channel junction. Both muscular bands are closely associated with the branchial nerves in the gill. When gills are exposed to 10-5 M serotonin in vitro, both ostial openings dilate and gill ciliary activity increases. The net result of serotonin treatment is an increase in ciliary activity, a maximal opening of the water canal ostia, and, presumably, an increase in water flow through the gill.

Effect of salt depletion on hydromineral balance in larval ambystoma gracile—II. Kinetics of ion exchange☆

Abstract 1. 1. Salt depletion reduces the renal and extra-renal efflux of Na, K and Cl from larval Ambystoma gracile . The decrease in Na and Cl efflux is interpreted in terms of an increased capacity for active transport of each ion. The minimum equilibrium concentration for Na is less than 0·01 m-equiv./l. 2. 2. Transferred to dilute solutions of NaCl, salt-depleted larvae (SDL) experience a net uptake of Na and Cl. This reflects an increase in the active influx of each ion. Michaelis-type kinetic analyses suggest that salt depletion increases V max . 3. 3. Na and Cl transport are not dependent. It is suggested that each system operates by exchanging for an endogenous ion of like charge, possibly Na/NH 4 and Cl/HCO 3 . 4. 4. Ionic homeostasis is discussed in terms of the regulation of specific transport systems located in various epithelia.

Effect of salt depletion on hydromineral balance in larval ambystoma gracile—I. ionic composition☆

Abstract 1. 1. Salt-depleted larval Ambystoma gracile (SDL) were compared with larvae maintained in pond water (non-depleted or NDL) with respect to ion and water content. 2. 2. About 25 per cent of the total Na in whole animals does not exchange with 22 Na in 12–24 hr. Salt depletion did not alter this fraction indicating that Na can be mobilized from this pool. The Na lost from the exchangeable pool is derived from both the intracellular and extracellular compartments. Body Cl exchanges completely with 36 Cl. Salt depletion causes a loss of Cl from both the extracellular and intracellular compartments. Salt depletion did not affect K content per unit weight. 3. 3. Of the total Na in rectus abdominis muscle about 30 per cent is slowly exchangeable in NDL and about 26 per cent in SDL. Exchangeable Na and Cl lost during depletion are derived from the extracellular space. 4. 4. Skin also containes a sizeable (25 per cent) slowly exchangeable Na pool part of which can be mobilized during depletion. Sodium is lost from the exchangeable fraction of extracellular and intracellular fluids. Chloride is apparently lost only from the extracellular space.

SODIUM TRANSPORT lN THE FRESHWATER ASIATIC CLAM CORBICULA FLUMINEA

The Na transport mechanism was examined in pondwater-acclimated (PW) and salt-depleted (SD) specimens of Corbicula fluminea. The Na influx in 0.5 mM Na2SO4 of 7.90 ± 0.79 µM Na/(g dry tissue·hr), higher than most freshwater animals, increased to 18.53 ± 2.10 µM Na/(g dry tissue·hr) in SD animals.Saturation of the transport system is typical of Michaelis-Menten enzyme kinetics. Maximum influx of PW clams was 12.90 ± 3.01 µM Na/(g dry tissue·hr), with a Km of 0.05 mM Na/l. The maximum rate in SD clams was 28.66 ± 2.17 µM Na/(g dry tissue·hr), with little change in Km.Sodium movement in C. fluminea may be partitioned into passive diffusion, excretion, exchange diffusion and active transport. Exchange diffusion comprises a substantial portion of Na movement: 5.91 ± 0.80 µM Na/(g dry tissue ·hr) in PW animals and 16.05 ± 0.67 µM Na/(g dry tissue·hr) in SD clams. Passive inward diffusion of Na was 0.50 µM Na/(g dry tissue·hr) for PW clams and 1.17 µM Na/(g dry tissue·hr) for SD clams.The primary exchange ion fo...

Paracellular Solute Uptake in the Freshwater Bivalves Corbicula fluminea and Toxolasma texasensis

Two species of freshwater bivalve were exposed to hyperosmotic solutions of various nonelectrolytes to compare the paracellular permeability of their gill epithelia. In Corbicula fluminea, exposure resulted in an elevation of blood solutes that was primarily due to dehydration. After 36 h of exposure, the concentration of Na in the blood decreased precipitously, and the nonelectrolyte accumulated. When lanthanum was added to the solution as a diffusion tracer, its electron-dense precipitate was rarely observed to penetrate the paracellular spaces of the gill epithelial cells in the absence of hyperosmotic stress. In contrast, precipitated lanthanum was commonly observed in the paracellular junctional complexes of the gill in animals that were subjected to hyperosmotic conditions. When the second species, Toxolasma texasensis, was exposed to hyperosmotic solutions of nonelectrolyte, dehydration appeared to be minimal and a seemingly normal concentration of ions was maintained in the blood. This, however, was because of the simultaneous loss of ions and water and a small gain in nonelectrolytes. Longer exposure (12 h or more) produced a precipitous decrease in most blood solutes and an extensive accumulation of nonelectrolyte. More lanthanum precipitate was seen in the paracellular spaces of both control and hyperosmotically stressed T. texasensis than in identically treated C. fluminea. We conclude that the epithelial junctions found in C. fluminea are relatively tight, which probably contributes to the ability of this species to maintain the solute in its body fluid at concentrations higher than are possible in T. texasensis.