Circadian rhythms of the parameters of the mouse esophagus epithelial cell kinetics

Circadian rhythms of the mitotic activity, DNA synthesis and the parameters of the mitotic cells of the mouse esophagus epithelium were studied during the periods of maximum and minimum proliferation. The number of mitoses and DNA-synthetizing cells increases rhythmically at 1--7 a. m. from 22 p. m. to 4 a. m., respectively. When 3H-thymidine was injected to the mice at 2 a. m., tG2min was 1h; tG2+1/2 M was 2h; tS was 7.1; tG1+1/2 M was 2h; tS was 7.1; tG1+1/2 M was 15.9h. When 3H-thymidine was injected at 2 p. m., tS rose up to 8.2 and tG1+1/2 M up to 14.8h. The mitotic cycle in both series of experiments totalled 25 h. Thus, the duration of various phases of the mitotic cycle depends on the time of the day and correlates with circadian rhythms of the mitotic activity and the number of DNA-synthetizing cells. Duration of the mitotic cycle of the cells passing through it at varying time of the day is the same and approximates the period of the circadian rhythm of mitoses and DNA synthesis in esophagus epithelium.     

Effect of graft versus host reaction on cell cycle time in neonatal mouse jejunum

The duration of cell cycle parameters in control mouse jejunum has been compared with that found following induction of a graft-versus-host reaction (GvHR) during the first 3 weeks of postnatal life. Values for tc and tG1 were found to decrease progressively during normal development: estimates for the whole crypt column in 21-day-old mice were approximately half to one quarter those found 6 days after birth 12.1 +/- 0.5 hr and 24.2 +/- 0.3 hr for tc; 2.8 +/- 0.3 hr and 12.1 +/- 0.3 hr for tG1 respectively; (means +/- SE). tS and tG2 were found to remain approximately constant during this period of neonatal development. Injecting foreign spleen cells into 3-day-old mice produced no effect on crypt cell proliferation or cell cycle parameters measured 3 days later. GvHR mice studied 8 days after spleen cell injection, however, showed both an increase in crypt cell proliferation and decreases in the values for tc and tG1 to levels similar to those normally found in 21-day-old control animals (tc 12.4 +/- 0.4 hr and tG1 5.4 +/- 0.4 hr for 11-day-old GvHR mice). The possible mechanism leading to these changes is discussed. The ability of GvHR to stimulate cell proliferation is used in the present work to test the hypothesis that the total number of cell divisions taking place after birth determines the temporal sequence of changes in disaccharidase content produced during neonatal development.     

Cell kinetics in the mouse esophageal epithelium in relation to the time of day

The kinetics of mouse esophageal epithelial cells was investigated throughout 90 h after a single injection of 3H-thymidine at 01 or at 13 h--the times of the peak and minimal magnitudes of the radioisotope index in the circadian rhythm of proliferation. The mitotic cycle parameters in the cells varied but insignificantly. For cells treated with 3H-thymidine at 01 h, T = 24.3 h, ts = 6 h, tG2 min = 1.5 h, tG2+ 1/2 M = 2.9 h and tG1+/2 M = 15.4 h; for those treated with 3H-thymidine at 13 h, T = 25.6 h, ts = 8.4 h, tG2 min = 1 h, tG2+ 1/2 M = 2.2 h, tG1+ 1/2 M = 15 h. Cells labeled at 01 h proliferated more actively for a long period of time as compared to those labeled at 13 h. The synchronism in undergoing several successive mitotic cycles was greater for cells labeled at the peak radioisotope index. The data obtained also suggest that the majority of cells enter the G0 phase after the completion of the first cycle. The duration of the G0 phase varies in different cell populations.     

Indices of mitotic cell division in sebaceous glands]

The main indices of mitotic cell division in rat sebaceous glands (external auditory meatus and tarsales gl.) were studied autoradiographically using H3-thymidine and with colchicine method. The duration of mitotic cycle and its separate phases, the number of cells involved in the proliferative pool, as well as the turnover of terminals of the epithelium in both the glands were stated to be nearly identical. The duration of the mitotic cycle was: T -- 28.1 hour; tG1 -- 18.64; tS -- 6.3; tG2 -- 1.80; tM -- 1.34 hours. The proliferative pool (Pc) -- 31.45%, turnover of the basal layer cells -- 89.25 hours. These indices for the stratified epithelium of excretory ducts were respectively; T -- 33.0 hours; tG1 -- 21.74; --8.06; tG2 -- 1.6; tM -- 1.6; Pc -- 26.8% and the turnover for the cells of the basal layer -- 123 hours. Thus, the sebaceous glands are to be regarded as organs where a rapid renovation of epithelia cells occurs.     

Kinetics of the oxidation of Rhus vernicifera stellacyanin by the Co(EDTA)-- ion.

A kinetic study of the oxidation of the copper(I) form of the blue copper protein stellacyanin (St(I) by Co(EDTA)-- has been performed. Observed rate constants approach a saturation limit with increasing [Co(EDTA)--] at pH 7, consistent with a mechanism involving rapid pre-equilibrium oxidant-protein complex formation followed by rate-limiting intramolecular Cu(I) to Co(III) electron transfer: Co(EDTA)-- + St(i Qp in equilibrium Co(EDTA)-- ---St(I) Co(EDTA)-- ---St(I) k2 leads to Co(EDTA)2-- ---St(II) (Qp = 149 M--1, k2 = 0.169 sec--1; 25.1 degrees, pH 7.0 mu 0.5 M (phosphate)). Activation parameters based on k2 (deltaH not equal to = 1.8 kcal/mol, deltaS not equal to = --56 cal/mol-deg) indicate that the electron transfer process is substantially nondiabatic, in marked contrast with results obtained for Co(phen) 3 3+ as the oxidant. Linear kobsd VS. [Co(EDTA)--] plots are reported for the Co(EDTA)-- oxidation of cuprous stellacyanin at pH 10 (k = 8.9 M--1 sec--1; 25.0, pH 10, mu 0.5 M (carbonate); DELTaH not equal to 11.3 kcal/mol, deltaS not equal to = -16 cal/mol-deg) and at pH 7 in the presence of excess EDTA (k = 21.2 M--1 sec--1; 25.1 degree, pH 7.0, mu 0.5 M (phosphate), [EDTA] tot = 5 X 10(--4) M; deltaH not equal to = 5.9 kcal/mol, delta S not equal to = --33 cal/mol-deg). It is concluded that Co(EDTA)-- adopts an electron transfer mechanism similar to that preferred by Co(phen)33+ under conditions where the oxidant is prevented from binding strongly to reduced stellacyanin.     

Autoradiographic studies of glial proliferation in different areas of the brain of the 14-day-old rat

Cell cycle parameters, as well as the mode of proliferation of glial cells, in four different areas of the brain of the 14-day-old rat (cortex, corpus callosum, nucleus caudatus putamen and commissura anterior) were studied using different cell kinetic methods after injection of [3H]TdR and/or [14C]TdR. The duration of the S phase (tS) was found to be about 10 hr and that of the cycle time (tC) about 20 hr, tG2 is less than 2 hr and t(G2 + M) about 4 hr. These values are valid for glial cells in all four brain areas studied. However, the labelling index (LI) of the glial cells differs by a factor of 3, between 1.8 and 5.4% in the different brain areas. Accordingly, the growth fraction of the glial cell population in the four areas varies between 0.04 and 0.12. Glial cells (astrocytes as well as oligodendrocytes) proliferate according to a steady state system. Furthermore, the proliferation of glial cells is associated with continuous cell loss. After each mitosis about 3% of the daughter cells become pyknotic and die. In addition, a permanent exchange of glial cells occurs between the proliferating and non-proliferating pool.     

Cell population kinetics in pig epidermis: further studies

The cell population kinetics of the epidermis were studied in 4-month-old pigs. Mitotic figures were confined to the basal cell (L1) and the first suprabasal cell layer (L2). The mitotic index (MI) was 0.17 +/- 0.04% for L1 and 0.08 +/- 0.03% for L2. Labelled nuclei were distributed throughout the viable epidermis, the majority (79.1 +/- 1.1%) were in L1 with 19.5 +/- 1.2% in L2. The labelling indices (LI) in layers L1 and L2 were 7.1 +/- 0.4% and 3.4 +/- 0.1%, respectively. After labelling with two injections of tritiated thymidine [3H]TdR separated by 90 min, the LI increased to 8.2 +/- 0.3% in L1 and to 4.0 +/- 0.2% in L2. This increased labelling confirmed that cell proliferation occurs in both layers, L1 and L2, of the epidermis. The cell production rate (K) in L1 and L2 had an upper limit of 10.7 +/- 1.0 and 6.2 +/- 1.8 cells per 1000 cells per hour respectively. The cell flow rate per hour (cell flux), into and out of the DNA synthesis phase (S), and the duration of DNA synthesis were determined from double-labelling studies with [3H]TdR and [14C]TdR. The cell flux into and out of S was identical and was calculated as 0.6 +/- 0.1%/hr (L1) and 0.5 +/- 0.1%/hr (L2). Values for tS varied from 8 to 10 hr. The cell turnover times (tT) were in the range 89-129 hr and 180-261 hr for L1 and L2, respectively. Log normal curves were fitted to the fraction labelled mitoses data for L1 and L2. Values for tS for cells in L1 and L2 were 9.8 hr and 11.9 hr, respectively. tG2 + 1/2tM was 7.2 hr in L1 and 9.1 hr in L2.     

Flow cytometric evaluation of cell cycle characteristics during in vitro differentiation of chick embryo chondrocytes

The cell cycle kinetic characteristics of chick endochondral chondrocytes differentiating in vitro were studied by flow cytometry. In addition, the synthesis of type I and type X collagens of the same cells was evaluated by immunoprecipitation. Dedifferentiated cells, derived from chick embryo tibiae and grown attached to a substratum, were characterized by type I collagen synthesis, a high growth fraction (GF = 0.94), minimal cell loss factor (phi = 0.02), and a total cell cycle time of the proliferating cells of about 17 h (tG1 = 8 h, tS = 5 h, and tG2 + M = 4 h). Transfer of dedifferentiated cells to suspension culture on agarose-coated dishes induced differentiation to hypertrophic chondrocytes. These were characterized by type X collagen synthesis, a low growth fraction (GF = 0.52), maximal cell loss factor (phi = 1.0), and a total cell cycle time of the proliferating cells of about 73 h (tG1 = 53 h, tS = 12 h, and tG2 + M = 8 h). The transition from dedifferentiated chondrocytes to hypertrophic chondrocytes was accompanied by large increases of the duration of all the cell cycle phases and of the number of quiescent and degenerating cells. Associated with these alterations in cell cycle kinetics was a switch from type I to type X collagen synthesis. Further preliminary data suggest that the population of differentiating chondrocytes (a state between dedifferentiated and hypertrophic chondrocytes) comprises a heterogeneous population of fast and slow growing cells.     

Intersubunit Disulfide Interactions Play a Critical Role in Maintaining the Thermostability of Glucose-6-phosphate Dehydrogenase from the Hyperthermophilic Bacterium Aquifex aeolicus

Proteins from thermophilic microorganisms are stabilized by various mechanisms to preserve their native folded states at higher temperatures. A thermostable glucose-6-phosphate dehydrogenase (tG6PDH) from the hyperthermophilic bacterium Aquifex aeolicus was expressed as a recombinant protein in Escherichia coli. The A. aeolicus G6PDH is a homodimer exhibiting remarkable thermostability (t_1/2=24 hr at 90°C). Based on homology modeling and upon comparison of its structure with human G6PDH, it was predicted that cysteine 184 of one subunit could form a disulfide bond with cysteine 352 of the other subunit resulting in reinforced intersubunit interactions that hold the dimer together. Site-directed mutagenesis was performed on tG6PDH to convert C184 and C352 to serines. The tG6PDH double mutant exhibited a dramatic decrease in the half-life from 24 hr to 3 hr at 90°C. The same decrease in half-life was also found when either C184 or C352 was mutated to serine. The result indicates that C184 and C352 may play a crucial role in strengthening the dimer interface through disulfide bond formation, thereby contributing to the thermal stability of the enzyme.     

EXPERIMENTAL CONTROL OF DNA SYNTHESIZING AND DIVIDING CELLS IN EXCISED ROOT TIPS OF PISUM

The number of dividing and DNA-synthesizing cells in excised pea roots can be regulated by eliminating the carbohydrate normally supplied in the culture medium. When the excised roots were allowed to remain for 24 hr in a medium lacking carbohydrate, the number of mitotic figures and tritiated thymidine (H³-T) labeled cells was reduced almost to zero. After an additional 24 hr in the incomplete culture medium, 15% of the interphase cells were H³-T labeled, the percentage of the cells that were dividing never exceeded 1.4, and 30% of these were H³-T labeled. When the roots remained in the deficient medium for 72 hr, neither cell division nor cells synthesizing DNA were observed. Upon addition of 2% sucrose, cell division and DNA synthesis were resumed in the roots that were maintained for 24 or 72 hr without an exogenous carbohydrate supply. It has been hypothesized that some proliferative systems consist of two cellular subpopulations which selectively stop or remain in either the pre-DNA synthetic (G₁) or post-DNA synthetic (G₂) periods of the mitotic cycle. The addition of sucrose, H³-T, and 5-aminouracil to the medium, after the roots had been maintained for 24 hr without a carbohydrate, indicated that most of the proliferative cells in the roots had accumulated in either G₁, a quasi-G₁ condition, i.e., DNA synthesis stopped sometime before completion, or G₂ periods of interphase; the majority, however, were in G₁ or quasi-G₁ conditions. The results suggested that DNA synthesis (S period) and mitosis or the onset of these processes have the highest metabolic requirements in the mitotic cycle and that G₁ and G₂ were the most probable states for proliferative cells in a meristem with a low metabolic level.     

Sex reversal in the medaka Oryzias latipes by brief exposure of early embryos to estradiol-17beta

To induce sex reversal of male to female, freshly-fertilized eggs of the S-rR strain medaka (Oryzias latipes) were immersed in saline containing estradiol-17beta (E2) in different concentrations for various durations until hatching. Results of the present experiment showed that the immersion duration in 1 microg/ml E2 to induce 100% reversal of sex differentiation in the genotypic males was enough only for one day (24 hr) post-fertilization (dpf) and that treatment with E2 for 1 dpf resulted in a dose-dependent manner with the maximum sex reversal of 100% at 1 microg/ml. To ascertain early developmental periods efficacious for inducing sex reversal, additional brief immersion treatments of eggs with E2 were further performed individually for four different early developmental periods (Stages 4-9, 10-12, 13-15 and 16-18) within 1 dpf. As a result, induction of sex reversal was observed in all these short immersion periods without any restricted efficacy. Between both experimental and control groups treated with or without E2 for 1 dpf, differences in the number of germ cells in a gonad were compared in newly-hatched fry. It was found that gonads of the genotypic males (XY) treated with E2 revealed the female type which contained many germ cells with much dividing activity. These data suggest that a possible switch mechanism that exogenous E2 could trigger to change the genetic cascades involved in sex determination upon fertilization exists in early developmental stages.     

5-AMINOURACIL TREATMENT : A Method for Estimating G2

Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G₂ transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G₂ + mitosis/2 of proliferating cells. Treatment with 5-AU can also be used to demonstrate the presence of subpopulations of dividing cells that differ in their G₂ duration. Using this method, 5-AU-induced inhibition, we have confirmed that in V. faba lateral roots there are two populations of dividing cells: (a) a fast-dividing population, which makes up ~85% of the proliferating cell population and has a G₂ + mitosis/2 duration of 3.3 hr, and (b) a slow-dividing population, which makes up ~15% of dividing cells and has a G₂ duration in excess of 12 hr. These estimates are similar to those obtained from percentage labeled mitosis (PLM) curves after incorporation of thymidine-³H.     

Antiprion compounds that reduce PrPSc levels in dividing and stationary-phase cells

During prion diseases, a normally benign, host protein, denoted PrP^C, undergoes alternative folding into the aberrant isoform, PrP^Sc. We used ELISA to identify and confirm hits in order to develop leads that reduce PrP^Sc in prion-infected dividing and stationary-phase mouse neuroblastoma (ScN2a-cl3) cells. We tested 52,830 diverse small molecules in dividing cells and 49,430 in stationary-phase cells. This led to 3100 HTS and 970 single point confirmed (SPC) hits in dividing cells, 331 HTS and 55 confirmed SPC hits in stationary-phase cells as well as 36 confirmed SPC hits active in both. Fourteen chemical leads were identified from confirmed SPC hits in dividing cells and three in stationary-phase cells. From more than 682 compounds tested in concentration–effect relationships in dividing cells to determine potency (EC₅₀), 102 had EC₅₀ values between 1 and 10 μM and 50 had EC₅₀ values of <1 μM; none affected cell viability. We observed an excellent correlation between EC₅₀ values determined by ELISA and Western immunoblotting for 28 representative compounds in dividing cells (R² = 0.75; p <0.0001). Of the 55 confirmed SPC hits in stationary-phase cells, 23 were piperazine, indole, or urea leads. The EC₅₀ values of one indole in stationary-phase and dividing ScN2a-cl3 cells were 7.5 and 1.6 μM, respectively. Unexpectedly, the number of hits in stationary-phase cells was ～10% of that in dividing cells. The explanation for this difference remains to be determined.     

Ultrastructural changes of radish leaf exposed to cadmium

Cadmium (Cd²⁺) is one of the most toxic heavy metal pollutants in nature. Mesophyll cells from the leaf of radish seedlings exposed to 0.25 and 1.0 mM of CdCl₂ during 24 h exhibited structural changes of chloroplasts, mitochondria and nuclei when compared to non-treated control plants. Chloroplasts from Cd²⁺-exposed samples exhibited changes in the organelle shape, an increase in the stroma volume and a deposition of electron-dense material in the double membrane. The changes in the chloroplast membranes were not very drastic, however and reorganization of the thylakoids and stroma was observed. In contrast, the breakdown of the nuclear envelope of the plant cells treated with Cd²⁺ was very clear. The accumulation of electron-dense granules was also observed in mitochondria. No alterations were observed in the vacuoles of radish seedlings grown at different Cd²⁺ concentrations for the periods tested.     

Phenotypic and functional properties of murine thymocytes. III. Kinetic analysis of the recovery of intrathymic cytolytic T lymphocyte precursors after in vivo administration of hydrocortisone acetate

The phenotypic and functional properties of cells in the C57BL/6 mouse thymus regenerating after a single dose of 100 mg/kg hydrocortisone acetate (H/C) are described. Functionally, the frequency of anti-H-2d cytolytic T lymphocyte precursors (CTL-P) in thymuses from individual mice was determined by limit dilution analysis of mixed leukocyte microcultures. The initial increase in CTL-P frequency, seen 48 hr post-H/C, was followed at 6 to 8 days by a phase of rapid decrease. The CTL-P frequency returned to a normal level by 28 days post-H/C. Analysis of the results from individual mice suggested that changes in total thymic CTL-P content were independent of the kinetics of thymus regeneration. Phenotypically, whereas the thymus 48 hr after H/C was considerably depleted of Lyt-2+ cells, there followed a rapid increase in the proportion of such cells to normal levels by 14 days post-H/C. In addition, as measured by FLS, a subpopulation of larger, predominantly Lyt-2+ cells was found during the phase of rapid thymic regeneration. With the use of a monoclonal anti-Thy-1.2 antibody, the weakly Thy-1-staining subpopulation of cells was absent from the thymus at 14 days post-H/C. These changes in the phenotypic properties of the post-H/C regenerating thymus were correlated with changes in their functional properties.     

Effects of bacterial lipopolysaccharide and calmodulin on Ca2(+)-ATPase and calcium in human natural killer cells, studied by a combined technique of immunoelectron microscopy and ultracytochemistry

Our previous studies indicate that bacterial lipopolysaccharide (LPS) enhances natural killer (NK) cell-mediated cytotoxicity and increases intracellular calcium (Ca2+) in hepatocytes. Calmodulin (CAM) regulates Ca2(+)-ATPase activity, intracellular Ca2+, and is also implicated in NK cell-mediated cytolysis. In the present work, the effects of LPS and CAM on Ca2(+)-ATPase and intracellular Ca2+ in human NK cells were studied by a combined technique of immunogold electron microscopy and ultracytochemistry. Peripheral blood mononuclear cells were treated with 100 micrograms/ml E. coli (0111:B4) LPS and/or 5 micrograms/ml CAM in RPMI 1640 medium at 37 degrees C for 1 or 4 hr. NK cells labeled with monoclonal anti-Leu-11a (CD16) antibody and colloidal gold-conjugated anti-mouse IgG were processed for cytochemical localization of Ca2(+)-ATPase and Ca2+. Ca2(+)-ATPase was localized in the plasma membrane of NK cells, and its activity was suppressed by LPS but was enhanced by CAM. However, no apparent changes in the enzyme reaction were observed when cells were exposed to CAM concomitantly with LPS or stimulated with LPS before CAM. Apparent reduction of the enzyme reaction was observed when LPS stimulation was preceded by CAM. Ca2(+)-ATPase reaction in mitochondria was observed only in NK cells exposed to CAM. Computer image analysis showed no changes in the intracellular Ca2+ in NK cells treated with LPS for 1 hr, whereas a significant increase in Ca2+ was found in cells exposed to LPS for 4 hr. The intracellular Ca2+ significantly decreased in NK cells treated with CAM or with a combination of LPS and CAM as compared to that of controls (p less than 0.05). The results indicate that CAM is capable of blocking or reversing the inhibitory effect of LPS on Ca2(+)-ATPase, and suggest that in human NK cells the plasma membrane-associated Ca2(+)-ATPase is responsible for extrusion of intracellular Ca2+.     

Studies on the population kinetics of the Walker carcinoma by autoradiography and pulse cytophotometry.

The proliferation parameters of the Walker carcinoma were estimated from both in vivo and in vitro measurements. tthe transplantable Walker carcinoma 256 was grown in male inbred BD1 rats. During exponential growth, 5--6 days after transplantation, a PLM curve was performed, yielding estimates of TC approximately equal to 18-0 hr, TS approximately equal to 6-4 hr, TG2+M approximately equal to 4-1 hr. With the double labelling technique in vitro under 2-2 atm oxygen we obtained: TC approximately equal to 18-2 hr, TS approximately equal to 8-2 hr, TG2+M approximately equal to 2-0 hr. From pulse cytophotometry DNA content histograms the fractions of cells in the cell cycle phases were calculated using a computer program: fG1 approximately equal to (47-6 +/- 1-1)%, fS approximately equal to (34-1 +/- 1-0)%, fG2+M approximately equal to (18-3 +/- 1-5)%. These fractions remained constant between the fifth and the twelfth day after transplantation. At that time the tumour growth had already slowed down appreciably. The growth fraction determined by repetitive labelling was 0.96 on the fifth and 0-93 on the seventh and eleventh day. The cell loss factor was phi approximately equal to 17% during exponential tumor growth and increased to about 100% between the tenth and twelfth day. The agreement of the cell kinetic data determined by autoradiography from solid tumours in vivo (PLM, continuous labelling) and autoradiography as well as pulse cytophotometry from in vitro experiments (excised material) was satisfactory.     

Inhibition of Mg2+ and Na(+)-K+ ATPases in selected tissues of fish, Cyprinus carpio under fenvalerate toxicity.

The changes in the magnesium adenosine triphosphatase (Mg2+ ATPase) and sodium-potassium adenosine triphosphatase (Na(+)-K+ ATPase) in gill, brain, liver and muscle tissues of freshwater fish, Cyprinus carpio at 6, 12, 24 and 48 hr exposure periods were studied after subjecting to sublethal concentration (10 micrograms/lit) of fenvalerate. Mg2+ ATPase and Na(+)-K+ ATPase activities were inhibited in all the tissues of fenvalerate exposed fish. The per cent inhibition increased with increase in the period of exposure and the possible reasons for the inhibition patterns are discussed.     

KINETICS OF THE INNER ENAMEL EPITHELIUM IN THE ADULT RAT INCISOR

Rats were injected with tritiated thymidine and sacrificed at various time intervals up to 24 hr. the extracted incisors were decalcified, cut sagittally, dipped into liquid emulsion exposed for 14 days, developed and stained. the counting consisted of an exact mapping and numbering of the cells.
The inner enamel epithelium consists of two compartments: proliferative and mature cells. the first may be further subdivided into blasts and metablasts. Each dividing blast yields one blast and one metablast. the metablasts continue to divide further, at least once, yielding again two metablasts.
The kinetic parameters of this population are: generation time 22 hr, synthesis time 4.5 hr, mitotic time 30 min, G₂ time 2 hr and G₁ time 15 hr. the daily cell production of the proliferative compartment equals its size.     

Short-term effects of mercury on survival, behaviour, bioaccumulation and ionic pattern in the catfish (Clarias lazera)

1. The fresh-water fish, Clarias lazera, was exposed to 13 lethal and sublethal concentrations of mercury. 2. The median tolerance limit (TLm) at different exposure periods, 24, 48, 72 and 96 hr, appears to be as follows: 0.96, 0.88, 0.81 and 0.72 ppm Hg2+/l, respectively. 3. From the subacute tests, the maximum acceptable toxicant concentration (MATC) for this fish was between 0.10 and 0.22 ppm Hg2+/l. 4. Behavioural changes, tissue Hg2+ distribution and serum ionic patterns were recorded during both the acute and subacute exposure periods.