Coral calcification: autoradiography of a scleractinian coral Galaxeafascicularis after incubation in 45Ca and 14C

 The uptake of ⁴⁵Ca and/or ¹⁴C by the skeleton of coral colonies has been commonly used to investigate the processes of calcification. This study reports the differential uptake of these tracers within different regions of the skeleton and tissues of individual corallites and polyps of the hermatypic coral Galaxea fascicularis. Incubation in ⁴⁵Ca in the light resulted in 80 percent of the ⁴⁵Ca taken up being deposited in the skeleton. Autoradiography of transverse and longitudinal slices of freeze-substituted polyps and corallites showed that in the light ⁴⁵Ca was incorporated into the exsert septa, the outside of the thecal walls of the corallite and the inner edges of the septa. Incorporation did not occur in the costae. The radioactivity in the skeleton was considerably greater than in the tissues. In the dark, or in the presence of the photosynthetic inhibitor Diuron, ⁴⁵Ca was taken up by the exsert septa and was patchily distributed in the corallite walls which suggests that it was not a result of isotopic exchange. The differential incorporation of ⁴⁵Ca onto the exsert septa was confirmed by scintillation counting. Negligible radioactivity remained in the extrathecal coelenteron after a brief 5 min rinse in non-radioactive seawater. Only 0.1% of ¹⁴C taken up in the light was incorporated into the skeleton and this was confirmed by autoradiography. In the presence of Diuron or in the dark, very little ¹⁴C was incorporated into tissues or skeleton and in autoradiographs was either not evident in the skeleton or the distribution was similar to that seen in autoradiographs of ⁴⁵Ca uptake. These results show that the deposition of ⁴⁵Ca, and therefore calcium carbonate, occurs at specific loci on the skeleton of a corallite. In the dark, deposition occurs specifically at the growing points of the corallite. Differential deposition of calcium carbonate within individual corallites has not been previously reported. Accepted: 27 May 1997     

Effects of mannan oligosaccharide dietary supplementation on performances of the tropical spiny lobsters juvenile (Panulirus ornatus,Fabricius 1798)

The effects of dietary mannan oligosaccharide (MOS) (Bio-Mos^®, Alltech, USA) on the growth, survival, physiology, bacteria and morphology of the gut and immune response to bacterial infection of tropical rock lobsters (Panulirus ornatus) juvenile were investigated. Dietary inclusion level of MOS at 0.4% was tested against the control diet (trash fish) without MOS inclusion. At the end of 56 days of rearing period, a challenged test was also conducted to evaluate the bacterial infection resistant ability of the lobsters fed the two diets. Lobster juvenile fed MOS diet attained 2.86 ± 0.07 g of total weigh and 66.67 ± 4.76% survival rate which were higher (P < 0.05) than the lobsters fed control diet (2.35 ± 0.14 g total weight and 54.76 ± 2.38% survival rate, respectively) thus providing the higher (P < 0.05) specific growth rate (SGR) and average weekly gain (AWG) of lobsters fed MOS diet. Physiological condition indicators such as wet tail muscle index (Tw/B), wet hepatosomatic index (Hiw) and dry tail muscle index (Td/B) of the lobsters fed MOS supplemented diet were higher (P < 0.05) than that of the lobsters fed the control diet. Bacteria in the gut (both total aerobic and Vibrio spp.) and gut's absorption surface indicated by the internal perimeter/external perimeter ratio were also higher (P < 0.05) when the lobsters were fed MOS diet. Lobsters fed MOS diet were in better immune condition showed by higher THC and GC, and lower bacteraemia. Survival, THC, GC were not different among the lobsters fed either MOS or control diet after 3 days of bacterial infection while bacteraemia was lower in the lobsters fed MOS diet. After 7 days of bacterial infection the lobsters fed MOS diet showed higher survival, THC, GC and lower bacteraemia than the lobsters fed the control diet. The experimental trial demonstrated the ability of MOS to improve the growth performance, survival, physiological condition, gut health and immune responses of tropical spiny lobsters juveniles.     

Calcium,potassium, and sodium exchange by full-grown and maturing Xenopus laevis oocytes

The kinetics of calcium, potassium, and sodium exchange by Xenopus laevis oocytes were monitored with radioactive tracers both before and during progesterone-induced maturation. The rate of ⁴⁵Ca release steadily elevates for several hours during maturation, beginning within 40 min after progesterone exposure. About an hour later, the rate of ⁴⁵Ca uptake also increases. The rate of ⁴⁵Ca release begins to decline 1–2 hr before germinal vesicle breakdown (GVBD); the rate of calcium uptake declines only after GVBD. Similar changes are seen after maturation is induced with other steroids, but not when maturation is blocked by inhibitors. The passive potassium flux initially increases after progesterone treatment to be followed later by a decrease. These observed changes occur coincidently with those of ⁴⁵Ca efflux. The passive sodium flux, on the other hand, steadily increases from the time of progesterone treatment until GVBD.     

Differential δC and δN signatures among scallop tissues: implications for ecology and physiology

There have been several studies where the isotopic composition of organisms has been determined seasonally, but fewer have examined separate organs. In this context, separate organs (e.g. gonad, digestive gland and muscle) of a suspension-feeder, the scallop Pecten maximus, were used to assess seasonal changes of both stable isotopes and biochemical components. Our study used multiple indicators [stable carbon and nitrogen isotope ratios, biochemical components and seston chlorophyll-a (chl a)] to track nutritive activity and energy allocation in P. maximus from the Bay of Brest (France). In addition to seasonal variation in the isotopic composition of P. maximus tissues, we found strong differences in the mean isotopic signatures of different organs. This has serious implications for interpretation of animal diets and potential use in animal physiology. Furthermore, we present evidence that seasonal variations of metabolism will cause changes in the isotopic composition not related to changes in the diet. Interpretation of isotopic data may require consideration of values from several separate organs. Finally, δ¹⁵N appears powerful to track metabolite fates in the scallop P. maximus.     

Nutritional indices of juvenile Caribbean spiny lobsters in a Mexican reef lagoon: Are changes over a 10-year span related to the emergence of Panulirus argus Virus 1 (PaV1)?

We compared two indices of nutritional condition, the relative weight of the digestive gland (RWDG) and the ratio of weight to carapace length (weight/CL ratio), of the first three benthic phases, algal juveniles (7–25 mm CL), postalgal juveniles (25–45 mm CL), and subadults (45–79 mm CL) of Caribbean spiny lobster (Panulirus argus) dwelling in a shelter-poor reef lagoon before (1995) and after (2005) deployment of large artificial shelters (“casitas”) in 1998. To provide an experimental baseline, in 2005 we also conducted a laboratory experiment to assess the effect of starvation on both nutritional indices. Through 25-day trials, starvation significantly decreased the mean RWDG of all three juvenile phases, but did not affect their weight/CL ratios. In the field, casitas significantly enhanced juvenile lobsters relative to control sites and to prior values, but between 1995 and 2005 there was a significant decrease in condition of algal juveniles (both indices) and postalgal juveniles (only the RWDG), but not of subadults. These results would appear to counter previous findings that, for P. argus, food is not limiting and nutritional condition is not density-dependent. However, in 2000, a new pathogenic virus that has a distinct predilection for small juveniles, Panulirus argus Virus 1 (PaV1), emerged in the reef lagoon. Among other effects, this lethal virus causes a marked atrophy of the digestive gland. Through the laboratory trials and in the field, prevalence of visibly diseased individuals was highest in algal juveniles and lowest in subadults. These individuals were excluded from statistical analyses, but the disease progression may affect the digestive gland progressively given that newly infected lobsters take several weeks to become visibly diseased. Up to 2006, PaV1 had not significantly impacted lobster density on casita sites, but because P. argus is highly gregarious and transmission of PaV1 appears to be mainly by contact, futher investigation is required. These issues are relevant to enhancement of spiny lobsters and assessment of ecological impacts of marine diseases.     

Effects of clomiphene and tamoxifen in vivo on the bone-resorbing effects of parathyroid hormone and of high oral doses of calcitriol (1,25(OH)2D3) in rats with intact ovarian function consuming low calcium diet

Two experiments were undertaken to study the abilities of clomiphene citrate (20 mg/kg body wt/wk s.c.) and tamoxifen citrate (20 mg/kg body wt/wk s.c.) to slow bone resorption mediated by (a) endogenous parathyroid hormone (PTH) and (b) exogenous calcitriol (1,25(OH)₂D₃) in vivo in rats with intact ovarian function. Groups of rats with ⁴⁵Ca-labelled bones were fed a low-calcium (0.01% Ca) diet to stimulate secretion of PTH. Neither clomiphene nor tamoxifen slowed the mobilization of ⁴⁵Ca from femoral bone or prevented the reduction in bone calcium induced by feeding this diet. Moreover these drugs did not depress the urinary excretion of ⁴⁵Ca or hydroxyproline. These observations indicated that clomiphene and tamoxifen did not inhibit PTH-mediated bone resorption. Administering calcitriol (50 ng/day) orally for 14 days raised plasma calcium, increased urinary ⁴⁵Ca and its specific activity and decreased femur ⁴⁵Ca: all these responses were similar in animal, receiving calcitriol alone and calcitriol with clomiphene or tamoxifen. The femur ⁴⁵Ca values (dpm × 10⁻³) were: (means ± SD, n = 8) placebo, 1901 ± 127; 1,25(OH)₂D₃, 1727 ± 96⁷; clomiphene + 1,25(OH)₂D₃, 1694 ± 93⁷; tamoxifen + 1,25(OH)₂D₃, 1664 ± 61⁷. (⁷ = P < 0.01). Thus neither clomiphene nor tamoxifen prevented calcitriol-mediated bone resorption in vivo in the rat.     

Calcium and pancreatic β-cell function 7. Evidence for cyclic AMP-induced translocation of intracellular calcium

The effect of cyclic AMP on calcium movements in the pancreatic β-cell was evaluated using an experimental approach based on in situ labelling of intracellular organelles of ob/ob-mouse islets with ⁴⁵Ca. Whereas the glucose-stimulated ⁴⁵Ca incorporation by mitochondria and secretory granules was increased under a condition known to reduce cyclic AMP (starvation), raised levels of this nucleotide (addition of 3-isobutyl-1-methylxanthine or N⁶,O^2′-dibutyryl adenosine 3′,5′-cyclic monophosphate) reduced the mitochondrial accumulation of ⁴⁵Ca. Conditions with increased cyclic AMP were associated with a stimulated efflux of ⁴⁵Ca from the secretory granules but not from the mitochondria. The microsomal fraction differed from both the mitochondrial and secretory granule fractions by accumulating more ⁴⁵Ca after the addition of 3-isobutyl-1-methylxanthine. The results suggest that cyclic AMP potentiates glucose-stimulated insulin release by increasing cytoplasmic Ca²⁺ at the expense of the calcium taken up by the organelles of the pancreatic β-cells.     

Removal of radioactive strontium from the rat by feeding stable strontium

The effect of administering the stable isotope of strontium (as phos-phate) at different dietary levels to adult rats (fed on a cereal and pulse-based diet containing 0.4% Ca) on the retention of radiostrontium (⁸⁹Sr) and radiocalcium (⁴⁵Ca) in the femur and the whole skeleton was studied for a period up to 6 weeks after an intraperitoneal injection of the two radioisotopes. The ability of strontium to remove⁸⁹Sr under the above dietary conditions was examined. Feeding Sr at 0.5% or 1% levels for 6 weeks had no effect on the skeletal content of⁸⁹Sr or⁴⁵Ca while a dietary regimen of 2% Sr (2000 times the normal content), significantly lowered the⁸⁹Sr and⁴⁵Ca content by about 30% in the femur but not in the whole skeleton. At this Sr level, the urinary excretion of the isotopes increased with a concomitant decrease in their excretion in the faeces. This study underscores the limitations of dietary Sr to mobilise⁸⁹Sr from the bones after it is incorporated in the bone mineral.     

Stable calcium isotope speciation and calcium oxalate production within beech tree (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) organs

In this study, we linked Ca speciation with isotope composition in plants. To do this, we performed leachate experiments to access the soluble Ca, structurally bound Ca and insoluble Ca (i.e., water and weak acid resistant) within beech tree organs (Fagus sylvatica L.). Ca isotopic measurements were combined with infrared spectroscopy and calcium oxalate biomineralization identification. The results from our study indicate that bark and leaves are the most enriched in monohydrated calcium oxalate crystals (whewellite), which are observable in parenchyma and sclerenchyma tissues, whereas roots and wood are enriched in structurally bound Ca. Our leaching experiments also show decreasing δ^44/40Ca isotopic signatures in the order of soluble Ca > structurally bound Ca > insoluble Ca. This finding implies that because leaves degrade faster than wooden organs and because Ca linked to pectate decomposes faster than Ca linked to oxalate crystals, differential Ca isotopic signatures are expected to be observed during litter degradation.     

The effect of aflatoxin B1 on the utilization of serum calcium

The mathematical analysis for plasma disappearance curve of aflatoxicosed animals, subsequently injected with ⁴⁵Ca was determined. The analysis showed that the three main compartments of the calcium pool (plasma, bone and the labile calcium pool on the surface of bone and soft tissues) had been affected. Specifically, the fractional rate constant for migration of ⁴⁵Ca from plasma pool to the labile pool had been diminished to its third value. This led to a corresponding reduction in the calcium content of the bone ash.The probable mechanism by which aflatoxin B₁ affects calcium dynamics may be interpreted by the inhibitory effect of aflatoxin in the hydroxylation mechanism of vitamin D₃ into an active intermediate. During aflatoxicosis (induction of 15 days) the animals entered a state of calcium deficiency, secondary to intestinal absorption inhibition. This was followed by bone resorption and disturbance of the fractional removal rate constant among different calcium compartments.     

Stable isotope fractionation in the digestive gland, muscle and gills tissues of the marine mussel Mytilus galloprovincialis

Mytilus galloprovincialis is a common species in the Mediterranean. It is a sedentary filter-feeding organism that assimilates carbon and nitrogen isotopic ratios in tissues from its food sources. The δ¹³C and δ¹⁵N values have been used to demonstrate differences in isotopic composition between digestive gland, muscle and gills of this mussel. For δ¹³C, mean values were - 21.99 ± 0.50‰, - 19.70 ± 0.44‰, and - 19.96 ± 0.44‰, respectively; and for δ¹⁵N, they were 5.16 ± 0.90‰, 7.67 ± 0.79‰ and 7.77 ± 0.85‰, respectively. The fractionation or enrichment factor for ¹³C values between digestive gland and muscle, between digestive gland and gills, and between muscle and gills were - 2.29 ± 0.16‰, - 2.04 ± 0.14‰ and 0.27 ± 0.07‰, respectively, within the expected range of ¹³C fractionation at filter feeders reported elsewhere. In contrast, low fractionation values were found for ¹⁵N with - 2.45 ± 0.24‰, - 2.51 ± 0.16‰ and - 0.11 ± 0.16‰, between digestive gland and muscle, between digestive gland and gills, and between muscle and gills, respectively. Through isotopic fractionation of M. galloprovincialis, the depleted values were found in the digestive gland, followed by gills and then by muscle tissue. Statistical analysis (PERMANOVA) was performed to check for significant differences in δ¹³C and δ¹⁵N isotopic signatures between tissues and localities. The current study demonstrates significant differences in the δ¹³C and δ¹⁵N isotopic composition between digestive gland, muscle and gills tissues in M. galloprovincialis living in the oligotrophic environment of the Balearic Islands.     

Calcium and pancreatic β-cell function: 4. Evidence that glucose and phosphate stimulate calcium-45 incorporation into different intracellular pools

β-Cell-rich pancreatic islets were microdissected from ob/ob-mice and used for studies of ⁴⁵Ca uptake and washout. Irrespective of whether the experiments were performed at 21 or 37°C both glucose and phosphate stimulated the net uptake of lanthanum-nondisplaceable ⁴⁵Ca. The stimulatory effect of phosphate was additive to that produced by glucose. ⁴⁵Ca incorporated in response to phosphate differed from that taken up in the presence of 20 mM glucose in being easily washed out although it was not affected by the glucose concentration of the washing medium. The efflux of ⁴⁵Ca was reduced after introducing phosphate into a medium used to perifuse islets which had accumulated ⁴⁵Ca in response to 20 mM glucose. This suggests that the outward calcium transport can be influenced also by intracellular trapping of the cation. The glucose-stimulated insulin release was inhibited by phosphate; an effect reversed by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. It is concluded that a common effect of glucose and phosphate is to trap calcium in the pancreatic β-cells but that there are fundamental differences between their effects on intracellular distribution of calcium and on insulin release.     

Regulation of calcium fluxes in rat pancreatic islets: Quinine mimics the dual effect of glucose on calcium movements

The effects of quinine and 9-aminoacridine, two blockers of potassium conductance in islet cells, on ⁴⁵Ca efflux and insulin release from perifused islets were investigated in order to elucidate the mechanisms by which glucose initially reduces ⁴⁵Ca efflux and later stimulates calcium inflow in islet cells. In the absence of glucose, 100 μM quinine stimulated ⁴⁵Ca net uptake, ⁴⁵Ca outflow rate and insulin release. Quinine also dramatically enhanced the cationic and the secretory response to intermediate concentrations of glucose, but had little effect on ⁴⁵Ca net uptake, ⁴⁵Ca fractional outflow rate and insulin release at a high glucose concentration (16.7 mM). The ability of quinine to stimulate ⁴⁵Ca efflux depended on the presence of extracellular calcium, suggesting that it reflects a stimulation of calcium entry in the islet cells. In the absence of extracellular calcium, quinine provoked a sustained decrease in ⁴⁵Ca efflux. Such an inhibitory effect was not additive to that of glucose, and was reduced at low extracellular Na⁺ concentration. At a low concentration (5 μM), quinine, although reducing ⁸⁶Rb efflux from the islets to the same extent as a non-insulinotropic glucose concentration (4.4 mM), failed to inhibit ⁴⁵Ca efflux. In the presence of extracellular calcium, 9-aminoacridine produced an important but transient increase in ⁴⁵Ca outflow rate and insulin release from islets perifused in the absence of glucose. In the absence of extracellular calcium, 9-aminoacridine, however, failed to reduced ⁴⁵Ca efflux from perifused islets. It is concluded that quinine, by reducing K⁺ conductance, reproduces the effect of glucose to activate voltage-sensitive calcium channels and to stimulate the entry of calcium into the B-cell. However, the glucose-induced inhibition of calcium outflow rate, which may also participate in the intracellular accumulation of calcium, does not appear to be mediated by changes in K⁺ conductance.     

Pitfalls of the 45Ca uptake method

The interpretation of the data derived from ⁴⁵Ca uptake measurements by cells and tissues can be difficult. Several of these difficulties and possible misinterpretations are described: 1) ⁴⁵Ca uptake is not equivalent to calcium influx; 2) interpretations based on the sole visual examination of ⁴⁵Ca uptake curves can be misleading because an increased tracer uptake can coexist with a decreased calcium transport and vice-versa; 3) drugs and hormones can have diametrically opposite effects when they are tested at steady state on in nonsteady state conditions. It is concluded that ⁴⁵Ca uptake curves must be kinetically analyzed and that the steady or non-steady state of the system must be known for a valid interpretation of such data.     

Trypsin inhibitor,mineral availability,and performance of broiler chickens fed on diets based on rice bran

Trypsin inhibitor in rice bran was inactivated by moist heat, but not by dry heating or treatments with 0.1% H₂SO₄, 0.1% NaOH or 0.1% NaCl. Heating rice bran could not improve its growth promotion value in the diet of broilers, which was related to the feed intake. Groundnut meal was the major protein supplement in the diets. Rice bran diets did not affect weight of pancreas (1.45–1.50 g/kg body weight). Use of ⁴⁵Ca revealed that availability of calcium on a rice bran diet was lower than on a maize-based diet. A similar effect on ⁵⁹Fe-availability was noted, although this result needs confirmation. Lack of differences in weight of thyroid glands and uptake of ¹³¹I by thyroids of birds on maize- and rice bran-based diets indicated the absence of any goitrogenic substance in the rice bran.     

Regulation of calcium fluxes in rat pancreatic islets: Calcium extrusion by sodium-calcium countertransport

Summary The mechanisms by which glucose regulates calcium fluxes in pancreatic endocrine cells were investigated by monitoring the efflux of⁴⁵Ca from prelabeled and perifused rat pancreatic islets. In the absence of both extracellular calcium and glucose, partial or total removal of extracellular sodium decreases the efflux of⁴⁵Ca from prelabeled islets. Glucose also reduces the efflux of⁴⁵Ca from islets perifused in the absence of extracellular calcium. This inhibitory effect of glucose on⁴⁵Ca efflux is decreased by half when the extracellular concentration of sodium is lowered to 24mm. In the absence of extracellular calcium but presence of glucose, partial or even total removal of extracellular sodium fails to decrease the efflux of⁴⁵Ca. At normal extracellular calcium concentration (1mm) partial removal of extracellular sodium dramatically increases⁴⁵Ca efflux from pancreatic islets. This increase in⁴⁵Ca efflux is partially but not totally suppressed by either 16.7mm glucose or cobalt. It is totally suppressed by 4.4mm glucose or by the combination of 16.7mm glucose and cobalt. At normal extracellular calcium concentration, glucose initially reduces and subsequently increases⁴⁵Ca efflux. The initial fall is unaffected by tetrodotoxin but decreased by 50% at low extracellular sodium concentration (24mm). The present results suggest the existence in pancreatic endocrine cells of a glucose-sensitive process of sodium-calcium counter-transport. By inhibiting such a process, glucose may decrease the efflux of calcium from islet cells. The effect of glucose is not mediated by an increase in intracellular sodium concentration. It could contribute to the intracellular accumulation of calcium which is thought to trigger insulin release.This paper is the IVth in a series.     

The diet of the Harlequin crab Lissocarcinus orbicularis,an obligate symbiont of sea cucumbers (holothuroids) belonging to the genera Thelenota,Bohadschia and Holothuria

The present paper characterizes, for the first time, the diet of the Harlequin crab Lissocarcinus orbicularis, an obligate symbiotic crab that associates with sea cucumbers (holothuroids) belonging to the genera Thelenota, Bohadschia and Holothuria. These tropical holothuroids host a rich symbiotic community in the Indo-West Pacific Ocean of which the Harlequin crab is the best known. The diet of L. orbicularis was characterized by analyzing the microscopic, molecular and isotopic signatures obtained from its gastric content. The presence of sea cucumber ossicles in the gastric mills of the crabs suggests that symbionts eat the superficial integument of their host and this was supported by the fact that Holothuroid DNA was detected in the stomach of L. orbicularis after DGGE and sequencing of the 18S rDNA gene. The stable isotopic δ¹³C and δ¹⁵N values of crab tissues were compared with diverse potential food sources including three holothuroids, three algae, one sea grass as well as the organic matter contained in the water column, in the sediment, and the second most abundant symbiont, the polychaete Gastrolepidia clavigera. The low δ¹⁵N values of crabs suggests that the crabs do not exclusively feed on sea cucumber tissue but assimilate diverse food sources such as sea grasses and organic matter contained in sediment that have similar δ¹³C values. There were no differences between the feeding of males and females but there was a positive correlation between the carapace length and the stable isotopic values indicating a shift of the food source as crabs grow larger.     

Comparison of injuries to New Zealand rock lobsters (Jasus edwardsii) caused by hand versus snare collection

Abstract

Following the prohibition in New Zealand of lobster snares in late 2005, we undertook research to compare the frequency and extent of injuries to rock lobsters (Jasus edwardsii) (Hutton) caused by recreational SCUBA divers using lobster snares compared with hand collection. Rock lobsters were sampled between January 2006 and October 2006 from multiple dive sites around the North Island of New Zealand. Of the 124 rock lobsters caught, 20.9% were in a soft shell state. Female rock lobsters constituted 43.5% of the catch, but only one was carrying eggs. Female mean tail width was 72.2 mm; male mean tail width was 71.9 mm. We found that hand collection caused significantly more injuries than snare collection, to both soft shell and hard shell animals. Hand collection also resulted in more major injuries, with 18% of hard shell animals and 31% of soft shell animals losing two or more limbs. We recommend that the prohibition on the use of rock lobster snares be lifted, as their use appears to significantly reduce injury and stress to rock lobsters in recreational dive areas, and increase the survival of undersized individuals released after capture.     

Effect of intracellular sodium on calcium uptake in isolated guinea-pig diaphragm and atria

(1) Effects of cellular sodium on the ⁴⁵Ca uptake of isolated guinea-pig diaphragm and atria were studied. (2) Cellular sodium and calcium contents were higher in diaphragm compared to atria after incubating the tissues in normal Krebs-Henseleit solution. (3) Cellular sodium content in atria and diaphragm were reduced signficantly by incubating the tissues in high potassium Krebs-Henseleit solution ($\text{K}{}^{\mathrm{+}}\text{= 34.7}\text{mM}$), while it was increased by incubating the tissues in the ice-cold low potassium and low calcium Krebs-Henseleit solution ($\text{K}{}^{\mathrm{+}}\text{= 0.65}\text{mM}$, $\text{Ca}{}^{\mathrm{2+}}\text{= 0.2}\text{mM}$). Cellular potassium content was changed inversely to the sodium content. (4) In atria, cellular content of calcium was not altered significantly by the above conditions. But in diaphragm, the cellular content of calcium was decreased slightly but significantly after incubation in the ice-cold low potassium and low calcium Krebs-Henseleit solution. (5) At normal cellular sodium levels, the ⁴⁵Ca uptake of both tissues was similar. (6) The reduction of the cellular sodium content caused a significant decrease in the ⁴⁵Ca uptake into both tissues. (7) When the cellular sodium content was increased in atrial preparations, a marked increase in the ⁴⁵Ca uptake was observed. On the other hand, in diaphragm preparations, only a slight increase was observed, even when cellular sodium content was much higher than the normal level. (8) These results indicate that even when the intracellular sodium is increased by some physiological of pharmacological events, calcium influx through Na⁺/Ca²⁺ exchange mechanism is very slight and slow in diaphragm.     

Rates of Turnover and Net Accretion of Calcium and the Role of Calcium Binding Polysaccharides During Calcification in the Calcareous Alga Halimeda opuntia (L.)

Calcification in the calcareous alga Halimeda opuntia involves Calcium exchange with the seawater. Calcium influx and-outflux is nearly the same and approximately 300 μg Ca/g alga/min. Calcium net accretion is 3.6 ± 1.1 μg Ca/g alga/min. Calcium outflux alga-seawater is higher in darkness than in light. Calcium exchange in live algae is 3–6 times faster than in dead algae. Calcium is lost from the seawater at two distinctly different rates and is taken up by watersoluble polysaccharides in the algal mucilage and by the skeleton. These two Calcium pools represent 0.1 and 99.9% of the algal Calcium respectively. Between 0.8–2.0% of the skeletal Calcium is exchangeable. The analysis of the ⁴⁵Ca specific activity curves suggests that there are more than 2 Calcium pools in the alga. The polysaccharides constitute a small but rapidly exchanging Calcium pool which communicates with the seawater and at least 2 other pools. The Calcium binding polysaccharides are involved in the Calcium metabolism of the alga and may play a role in algal calcification.