Serum parameters of Adriatic sturgeon Acipenser naccarii (Pisces: Acipenseriformes): effects of temperature and stress

Data on the concentrations of some blood constituents of captive Adriatic sturgeon, Acipenser naccarii, a primitive bony fish, are reported. Serum osmolality, Na⁺, K⁺, Cl⁻, Ca²⁺, cortisol, glucose and total protein concentrations were measured. The effects of anaesthesia, temperature, crowding and prolonged handling stress were tested on a group of 12 4-year-old sturgeons sampled repeatedly. The anaesthetic dose of MS 222 (140 mg l⁻¹) induced significant osmolality elevation in the sturgeon. After exposure to colder temperature (17 versus 25°C), cortisol and Cl⁻ concentrations significantly decreased. The cultured sturgeon did not seem susceptible to crowding and prolonged handling stress, since neither the serum cortisol and glucose levels nor the other blood parameters were affected by these stressors. Results are compared with the few available data on other chondrostean fish and with those on teleosts.     

Cold-induced cytosolic free calcium ion concentration changes in wheat

Relatively little is known about changes in the cytosolic free calcium ion concentration ([Ca²⁺]_c) in monocotyledonous plants. Therefore, we produced transgenic winter wheat lines stably expressing the calcium-sensitive photoprotein aequorin constitutively in the cytosol. [Ca²⁺]_c was detected in vivo by luminometry, and [Ca²⁺]_c elevations were imaged at video rate. Experiments with the transgenic seedlings focused on potential changes in [Ca²⁺]_c during cold exposure. Temperature-induced changes in [Ca²⁺]_c were found to be more dependent on the change in temperature (dT dt⁻¹) than on the absolute value of temperature. [Ca²⁺]_c increased only at cooling rates higher than 8°C min⁻¹, indicating that an overall cellular [Ca²⁺]_c increase is of minor relevance as a signal for cold acclimation in wheat under ecological conditions. The results are discussed with regard to the so-called ‘calcium signature hypothesis’.     

Effects of growth conditions on exopolysaccharide production by Cyanospira capsulata

Batch cultures of Cyanospira capsulata, a heterocystous cyanobacterium possessing a thick polysaccharidic capsule, were characterized by increasing viscosity owing to the continuous release of a soluble polysaccharide (EPS) into the culture medium. Both capsulated trichomes and solubilized EPS contributed to the flow properties of whole cultures. A typical pseudoplastic behaviour, the more marked the more aged were the cultures, was evidenced.The production of EPS was investigated under different growth conditions by changing some nutritional and physical parameters known to affect the synthesis of exopolysaccharides in algae and cyanobacteria. Among the factors tested (Ca²⁺, Mg²⁺ or PO₄⁻⁴ deficiencies, salinity and pH) only Mg²⁺ shortage caused a significant enhancement of the EPS production. Under continuous illumination in open ponds, the EPS productivity of batch cultures on standard mineral medium was about 5·8 g m⁻² day⁻¹, whereas under Mg²⁺ deficiency with a consequent increase of the cultures' viscosity     

Specific cation modulation of anion transport across the human erythrocyte membrane

The specific modulation by three cations, Ca²⁺, Mg²⁺, and tetracaine of the equilibrium exchange of SO₄²⁻ across the erythrocyte membrane was investigated. While external calcium had no effect on SO₄²⁻ exchange, internal calcium, and external calcium in the presence of 10 μM A23187 were found to be potent inhibitors of the exchange reaction. The apparent inhibition constants (K₁) for Ca²⁺ were calculated to be 6.1 μM and 5 μM for the above two conditions, respectively.Unlike Ca²⁺, Mg²⁺ was shown to be a weak activator of SO₄²⁻ exchange with an apparent dissociation constant of 3.6 μM. Competition experiments demonstrated that the Ca²⁺ and Mg²⁺ sites associated with anion transport are distinct and noninteracting.Tetracaine, a cation at neutral pH, was also found to be an inhibitor of SO₄²⁻ exchange with an apparent K₁ of 0.8 mM. Although tetracaine was observed to displace calcium from non-specific sites on the erythrocyte membrane, it showed no effect on the apparent inhibition constant of Ca²⁺ for SO₄²⁻ exchange. Thus, the Ca²⁺ and tetracaine sites also appear to be independent. The difficulty of situating three mutually independent sites on a single subunit protein, i.e., band 3, is considered.Using the experimental data obtained from five individuals, the concentration of free calcium in the red cell cytoplasm was calculated to range from 0.2 to 0.7 μM. This concentration was sufficient to reduce SO₄²⁻ exchange only 3–8%. It was concluded that calcium inhibition of anion exchange, and, hence, impairment of CO₂ transport, may be physiologically significant only in senescent cells and in certain types of anemia where calcium concentrations are significantly increased.     

Microfluorometric analysis of Cl permeability and its relation to oscillatory Ca signalling in glucose-stimulated pancreatic β-cells

The cytoplasmic concentrations of Cl⁻([Cl⁻]_i) and Ca²⁺ ([Ca²⁺]_i) were measured with the fluorescent indicators N-(ethoxycarbonylmethyl)-6-methoxyquinilinum bromide (MQAE) and fura-2 in pancreatic β-cells isolated from ob/ob mice. Steady-state [Cl⁻]_i in unstimulated β-cells was 34 mM, which is higher than expected from a passive distribution. Increase of the glucose concentration from 3 to 20 mM resulted in an accelerated entry of Cl⁻ into β-cells depleted of this ion. The exposure to 20 mM glucose did not affect steady-state [Cl⁻]_i either in the absence or presence of furosemide inhibition of Na⁺, K⁺, 2 Cl⁻ co-transport. Glucose-induced oscillations of [Ca²⁺]_i were transformed into sustained elevation in the presence of 4,4′ diisothiocyanato-dihydrostilbene-2,2′-disulfonic acid (H₂DIDS). A similar effect was noted when replacing 25% of extracellular Cl⁻ with the more easily permeating anions SCN⁻, I⁻, NO₃⁻ or Br⁻. It is concluded that glucose stimulation of the β-cells is coupled to an increase in their Cl⁻ permeability and that the oscillatory Ca²⁺ signalling is critically dependent on transmembrane Cl⁻ fluxes.     

Stimulation of Ca efflux by N-formyl chemotactic peptides in guinea-pig peritoneal macrophages

Effects of N-formyl chemotactic peptides on the Ca²⁺ influx and efflux were investigated in guinea-pig peritoneal macrophages using an isotope tracer. fMet-Leu-Phe did not enhance the influx of ⁴⁵Ca²⁺ into macrophages, whereas it stimulated the efflux of ⁴⁵Ca²⁺ from macrophages at concentrations ranging from 10⁻¹⁰ M to 10⁻⁷ M. fMet-Met-Met and fMet-Leu also stimulated the ⁴⁵Ca²⁺ efflux, albeit at much higher concentrations, while there was no stimulation with fMet. The mitochondrial inhibitors, oligomycin and NaN₃, did not modify the ⁴⁵Ca²⁺ efflux induced by the chemoattractants, yet they did induce the release of ⁴⁵Ca²⁺ from the mitochondria. On the other hand, higher concentrations of the calmodulin antagonists, chlorpromazine and trifluoperazine, induced the release of ⁴⁵Ca²⁺ from the NaN₃-insensitive Ca²⁺ store site and mimicked the enhancement of the ⁴⁵Ca²⁺ efflux by N-formyl chemotactic peptides. Thus, N-formyl chemotactic peptides appear to increase the levels of intracellular free Ca²⁺ in guinea-pig peritoneal macrophages, probably by inducing the release of Ca²⁺ from the NaN₃-insensitive Ca²⁺ store site.     

Vanadate inhibition of the Ca-ATPase from human red cell membranes

1. (1) VO₃⁻ combines with high affinity to the Ca²⁺-ATPase and fully inhibits Ca²⁺-ATPase and Ca²⁺-phosphatase activities. Inhibition is associated with a parallel decrease in the steady-state level of the Ca²⁺-dependent phosphoenzyme.

2. (2) VO₃⁻ blocks hydrolysis of ATP at the catalytic site. The sites for VO₃⁻ also exhibit negative interactions in affinity with the regulatory sites for ATP of the Ca²⁺-ATPase.

3. (3) The sites for VO₃⁻ show positive interactions in affinity with sites for Mg²⁺ and K⁺. This accounts for the dependence on Mg²⁺ and K⁺ of the inhibition by VO₃⁻. Although, with less effectiveness, Na⁺ substitutes for K⁺ whereas Li⁺ does not. The apparent affinities for Mg²⁺ and K⁺ for inhibition by VO₃⁻ seem to be less than those for activation of the Ca²⁺-ATPase.

4. (4) Inhibition by VO₃⁻ is independent of Ca²⁺ at concentrations up to 50 μM. Higher concentrations of Ca²⁺ lead to a progressive release of the inhibitory effect of VO₃⁻.

Activators of the ATP-dependent surface reaction in the apical cell membrane of the bull-sperm head, causing head-to-head association

Mg²⁺, Ca²⁺ and Mn²⁺ were found to act as activators of the ATP-dependent surface reaction, leading to head-to-head association in bull spermatozoa. Ca²⁺ was more efficient than Mg²⁺, while Zn²⁺, like Na⁺ + K⁺ in combination with Mg²⁺, seemed to have no such effect. High ionic strength induced head-to-head association, as did higher concentrations of Mg²⁺ and Ca²⁺ than those necessary for the activation of ATP, Ca²⁺ acting in a lower conc. than Mg²⁺. To this effect was added that of the ATP-dependent reaction when ATP was also present. As activators, Mg²⁺ and Ca²⁺ did not potentiate each other; their effects were cumulative when the ions acted together.When the ATP concentration within the range 1 × 10⁻⁵ to 8 × 10⁻⁵ M was increased stepwise in the presence of 2 × 10⁻⁵ M Mg²⁺ or Ca²⁺, the association resulting from each single concentration step progressively increased. At low cation concentrations, the increase was about the same for the two cations: at higher concentrations it was much steeper in the presence of Ca²⁺ than in that of Mg²⁺. In the latter case, it was not statistically significant above 4 × 10⁻⁵ M ATP.Increasing the cation concentration in the range 1 × 10⁻⁵ to 4 × 10⁻⁵ M in the presence of 2 × 10⁻⁵ M ATP produced an immediate high increase in association, which was followed by a lower increase. The optimum concentration ratio for Mg²⁺:ATP was at least 1:1 and for Ca²⁺: ATP at least 1.5:1.Oubain, containing enone structure, abolishes association.     

Remediation of depleted soils by addition of ion exchange resins

Parallel investigations with fertility were carried out in standard garden soil with ion exchange substrate BIONA 111 as well with mixtures in different proportions. The ion exchange substrate was a mixture of ion exchange resins saturated in certain proportions with a complete set of biogenic ions. Plant productivity in the ion exchange substrate in a 6-week vegetation period was 950 g/kg of the green biomass compared with 29 g/kg in soil. Productivity linearly depended on the mass fraction of the ion exchange substrate in the mixtures with the garden soil. Addition of 1% of the ion exchange substrate is sufficient for starting vegetation in completely depleted soil and barren sand. Addition of different ionic forms of ion exchange resins (K⁺, Ca²⁺+Mg²⁺+K⁺, NO₃⁻, NO₃⁻+H₂PO₄²⁻+SO₄²⁻) caused pronounced positive effects on soil productivity though these effects were less significant than those of ion exchange substrate. Addition of ion exchange substrates can be an efficient means for remediation of destroyed soils and fruitless rocks.     

Dual effect of adrenalin on sugar transport in rat diaphragm muscle

The effect of adrenalin on the membrane transport of the non-metabolized sugar, 3-methylglucose, was studied in isolated “intact” rat hemidiaphragms and related to simultaneously occurring changes in the internal levels of Na⁺, ATP, glucose-6-P, glycerol formation and ⁴⁵Ca uptake and loss. Basal sugar transport was inhibited by low (10⁻⁸−10⁻⁵ M) concentrations of adrenalin; this was antagonized by propranolol and practolol. High concentrations (10⁻⁴−10⁻³ M) stimulated sugar transport, and this was blocked by propranolol and butoxamine and was dependent on external Ca²⁺. These results suggest interaction with two different classes of adrenergic receptors, possibly of β₁ and β₂ types. Both low and high concentrations increased Na⁺ and K⁺ gradients by a practolol-sensitive effect. Isoproterenol behaved identically but phenylephrine had only the two practolol-sensitive effects on sugar and ion transport. Insulin did not interfere with inhibition of sugar transport and decrease in internal Na⁺ but prevented stimulation of sugar transport. Under anoxia adrenalin had no effect on sugar transport but led to greater Na⁺ gain by tissue. Addition of 3.0 mM palmitate decreased inhibition of sugar transport without changing receptor specificity. ATP was decreased and lipolysis enchanged by high adrenalin but glucose-6-P was increased by the low concentration as well. Influx of ⁴⁵Ca was decreased by low and increased by high adrenalin; ⁴⁵Ca efflux was also differentially affected. The results indicate that inhibition and stimulation of sugar transport depend on different receptors and that the latter response may override the former. The data are consistent with the earlier postulated regulatory role of sarcoplasmic Ca²⁺ on sugar transport in muscle, with adrenalin affecting Ca²⁺ fluxes and distribution both directly and indirectly.     

The amount of acetylcholine mobilisable Ca in single smooth muscle cells measured with the exogenous cytoplasmic Ca buffer, Indo-1

Single smooth muscle cells from guinea pig urinary bladder were voltage clamped with patch electrodes containing 1 mM Indo-1. As Indo-1 entered the cell, Δ[Ca²⁺]_i in response to Ca²⁺, influx with I_Ca (1 s steps to -10 mV) was progressively decreased. ΔF₄₁₀ was used as a measure of the Ca²⁺ amount bound to Indo-1. Within less than 2 min after establishment of the whole-cell configuration, the fraction of Ca²⁺ entering the cell with I_Ca which binds to Indo-1 became constant, suggesting that Indo-1 completely overrides the endogenous Ca²⁺ buffers. Under these conditions, ΔF₄₁₀ was satisfactorily fitted with the time integral of I_Ca during 1 s long steps. Acetylcholine (ACh, 50 μM) was rapidly applied to Indo-1 loaded cells to induce IP₃-induced Ca²⁺ release (IICR), which peaked within about 1 s. From ΔF₄₁₀ in response to I_Ca and ACh and from the time integral of I_Ca the amount of Ca²⁺ released during IICR was estimated to be 680 attomole (680 × 10⁻¹⁸ mole), corresponding to 230 μM for 3 pl of accessible cytoplasmic volume.     

The α1-adrenergic receptor in human erythrocyte membranes mediates interaction in vitro of epinephrine and thyroid hormone at the membrane Ca-ATPase

Membrane Ca²⁺-ATPase activity was stimulated in vitro separately by T₄ (10⁻¹⁰ M) and by epinephrine (10⁻⁶ M). In the presence of a fixed concentration of T₄, additions of 10⁻⁸ and 10⁻⁶ M epinephrine reduced the T₄ effect on the enzyme. β-Adrenergic blockade with propranolol (10⁻⁶ M) prevented stimulation by epinephrine of Ca²⁺-ATPase activity, but did not prevent the suppressive action of epinephrine on T₄-stimulable Ca²⁺-ATPase. In contrast α₁-adrenergic blockade with unlabelled prazosin restored the effect of T₄ on Ca²⁺-ATPase activity in the presence of epinephrine. Like propranolol, prazosin prevented enhancement of enzyme activity by epinephrine in the absence of thyroid hormone. Neither prazosin nor propranolol had any effect on the stimulations by T₄ of red cell Ca²⁺-ATPase in the absence of epinephrine. Analysis of radiolabelled prazosin binding to human red cell membranes revealed the presence of a single class of high-affinity binding sites (K_d, 1.2 × 10⁻⁸ M; B_max, 847 fmol/mg membrane protein). Thus, the human erythrocyte membrane contains α₁-radrenergic receptor sites that are capable of regulating Ca²⁺-ATPase activity.     

Antagonistic effect of calcium, zinc and selenium against cadmium induced chromosomal aberrations and micronuclei in root cells of Hordeum vulgare

The antagonistic effect of calcium (Ca²⁺), zinc (Zn²⁺) and selenium (Se⁴⁺) at different concentrations (10⁻²–10⁻⁶ M) against cadmium (Cd²⁺) induced genotoxic effects in root cells of Hordeum vulgare were studied. The results showed that 10⁻³–10⁻⁵ M could induce chromosomal aberrations and micronuclei formation. But in the treatment with 10⁻²–10⁻⁶ M of Ca²⁺, Zn²⁺ and Se⁴⁺ together with Cd²⁺ (10⁻³–10⁻⁵ M), respectively, the frequencies of chromosomal aberrations and micronuclei effectively decreased after 48 h of treatment. The treatment with 10⁻⁴–10⁻⁶ M of Ca²⁺ together with 10⁻⁴–10⁻⁵ M Cd²⁺, 10⁻⁶ M of Zn²⁺ together with 10⁻⁵ M Cd²⁺ and 10⁻⁶ M of Se⁴⁺ together with 10⁻⁵ M Cd²⁺ suggested rather obvious antagonistic effects. The order of the antagonisms of Ca²⁺, Se⁴⁺ and Zn²⁺ against Cd²⁺ toxicity was Ca²⁺>Se⁴⁺>Zn²⁺. The degree of antagonisms of Ca²⁺, Se⁴⁺ and Zn²⁺ against Cd²⁺ related to their concentration ratio.     

Effects of neuropathy on high-voltage-activated Ca current in sensory neurones

Voltage-dependent Ca²⁺ channels (VDCCs) have emerged as targets to treat neuropathic pain; however, amongst VDCCs, the precise role of the Ca_V2.3 subtype in nociception remains unproven. Here, we investigate the effects of partial sciatic nerve ligation (PSNL) on Ca²⁺ currents in small/medium diameter dorsal root ganglia (DRG) neurones isolated from Ca_V2.3(−/−) knock-out and wild-type (WT) mice. DRG neurones from Ca_V2.3(−/−) mice had significantly reduced sensitivity to SNX-482 versus WT mice. DRGs from Ca_V2.3(−/−) mice also had increased sensitivity to the Ca_V2.2 VDCC blocker ω-conotoxin. In WT mice, PSNL caused a significant increase in ω-conotoxin-sensitivity and a reduction in SNX-482-sensitivity. In Ca_V2.3(−/−) mice, PSNL caused a significant reduction in ω-conotoxin-sensitivity and an increase in nifedipine sensitivity. PSNL-induced changes in Ca²⁺ current were not accompanied by effects on voltage-dependence of activation in either Ca_V2.3(−/−) or WT mice. These data suggest that Ca_V2.3 subunits contribute, but do not fully underlie, drug-resistant (R-type) Ca²⁺ current in these cells. In WT mice, PSNL caused adaptive changes in Ca_V2.2- and Ca_V2.3-mediated Ca²⁺ currents, supporting roles for these VDCCs in nociception during neuropathy. In Ca_V2.3(−/−) mice, PSNL-induced changes in Ca_V1 and Ca_V2.2 Ca²⁺ current, consistent with alternative adaptive mechanisms occurring in the absence of Ca_V2.3 subunits.     

Seasonal changes of ionic concentrations in the vacuolar sap of Chara vulgaris L. growing in a brackish water lake

Summary The composition of the vacuolar sap of Chara vulgaris growing in a brackish water lake was estimated weekly over 2 years (1984–1985). The ionic concentrations of the main cations Na⁺, K⁺, Ca²⁺, and Mg²⁺ and the anion Cl^- varied depending on cell age, developmental state, and season. The average of all measurements (in mM) was Na⁺: 35, K⁺: 106, Ca²⁺: 7, Mg²⁺: 23, Cl^-: 101, SO _2- ⁴ : 20, and PO _3- ⁴ : 5. At the onset of growth in May/June the ionic content was lower compared to the mean value for the year, steadily increasing until it reached its maximum above the annual mean in winter. During the period of fructification (sexual reproduction: formation of antheridia and oogonia), when up to 100 mM sucrose was accumulated in the vacuolar sap, ionic content was lowest. This resulted in a fairly constant osmotic potential throughout the year. Mg²⁺ and Ca²⁺ concentrations were correlated with the physiological age of the cells.     

Calcium-dependent adenylate cyclase of pituitary tumor cells

Effects of Ca²⁺ and calmodulin on the adenylate cyclase activity of a prolactin and growth hormone-producing pituitary tumor cell strain (GH₃) were examined. The adenylate cyclase activity of homogenates was stimulated approx. 60% by submicromolar free Ca²⁺ concentrations and inhibited by higher (μM range) concentrations of the cation. A 2–3-fold stimulation of the activity in response to Ca²⁺ was observed at physiologic concentrations of KCl, with both the stimulatory and inhibitory responses occurring at respectively higher free Ca²⁺ concentrations. Calmodulin in incubations at low KCl concentrations increased the enzyme activity at all Ca²⁺ concentrations tested. In incubations conducted at physiologic KCl concentrations, both the inhibitory and stimulatory responses to Ca²⁺ were shifted by calmodulin to lower respective concentrations of the cation, without significant change occurring in the maximal rate of enzymic activity at optimal free Ca²⁺. Mg²⁺ concentrations in the incubation also influenced the Ca²⁺ concentration dependence of adenylate cyclase; at high Mg²⁺ more Ca²⁺ was required to obtain maximal activity. Trifluoperazine inhibited adenylate cyclase of GH₃ cells only in the presence of Ca²⁺; as Ca²⁺ concentrations in the assay were increased, higher drug concentrations were required to inhibit the enzyme. Ca²⁺ was also observed to reduce the extent of enzyme destabilization which occurred during pretreatments at warm temperatures. Vasoactive intestinal polypeptide and phorbol myristate acetate, which stimulate prolactin secretion in intact GH₃ cells, enhanced enzyme activity 4- and 2.5-fold, respectively, without added Ca²⁺. Increasing free Ca²⁺ concentrations reduced the enhancement by VIP and eliminated the stimulation by PMA.     

Major ions,nutrients and primary productivity in volcanic neotropical streams draining rainforest and pasture catchments at Los Tuxtlas,Veracruz, Mexico

Six streams in the Los Tuxtlas region, a volcanic area in southeastern Mexico, were characterized chemically and biologically. Temperature, pH, conductivity, ions (Ca²⁺, Mg²⁺, Na⁺, K⁺, CaCO^– ₃ and SO^2- ₄), nutrients (NO^– ₃, NH⁺ ₄, total P and PO^–3 ₄), and chlorophyll a from epilithon were measured every other month from September 1996 to July 1997. The streams studied had a consistent pattern of cation dominance (Na⁺>Ca²⁺>Mg²⁺>K⁺), and ionic concentrations varied little during the year of study; nutrients, however, showed strong temporal variability. The ion chemistry of the streams was influenced by bedrock weathering according to the Gibbs Model. The streams are chiefly mesotrophic, but their primary production may be limited by nitrogen based on the N:P ratio. Streams differed in chlorophyll a concentrations and their productivity changed temporally. They were among the most mineral-rich tropical streams, and both their ion concentration levels and cationic patterns coincided with other neotropical volcanic streams. Although there was a pattern in which ion concentrations of the streams were negatively related to the proportion of conserved vegetation and positively related to the proportion of pastures and croplands, the relationships were not statistically significant. We concluded that differences in the major ions of the streams studied were caused by the great heterogeneity in geology and soil types, as well as by geothermal activity in the area. Temporal changes in nutrients were related to biological processes in the streams that influenced primary productivity. Moreover, the influence of land use might be hidden by the strong effect of this heterogeneity on the streams studied.     

Effects of intracellular Ca2+ chelation on the light response in Drosophila photoreceptors

In order to test the hypothesis that excitation in Drosophila photoreceptors is mediated by Ca²⁺ released from internal stores, the Ca²⁺ buffers EGTA, BAPTA and di-bromo-BAPTA (DBB) were introduced into dissociated photoreceptors via whole-cell recording pipettes. All buffers were preloaded with Ca²⁺ to provide the same free Ca²⁺ concentration (250 nM). EGTA (up to 18 mM free buffer) had only weak effects upon voltage-clamped flash responses in normal Ringer's solution (1.5 mM Ca ₀ ²⁺ ), and no effect in Ca²⁺-free solution. The maximum BAPTA concentration tested (14.4 mM free BAPTA) reduced the initial rate of rise by ca. 5000-fold in normal Ringer's solution; by ca. 500-fold in Ca²⁺free solution; and only ca. 60-fold in the absence of Mg²⁺, which preferentially blocks one component of the light-sensitive current. Although BAPTA delayed the time-to-peak in normal Ringer's solution, responses in Ca²⁺ free Ringer's solution were accelerated. These results support the role of Ca²⁺ influx in regulating sensitivity and response kinetics; however, in view of the high concentrations required to attenuate responses in Ca²⁺ free Ringer's solution, the role of Ca²⁺ release in excitation remains unclear. DBB was ca. 2–3 fold more potent than BAPTA, and at concentrations > 5 mM had a qualitatively different action, greatly delaying the time-to-peak. This suggests DBB may have distinct pharmacological actions or access to compartments inaccessible to BAPTA.The only current activated by introducing 5–500 M Ca²⁺ (buffered with nitrilo-triacetic acid) was electrogenic Na⁺/Ca²⁺ exchange. When this was blocked by removing Nao ₀ ⁺ , a novel cationic conductance was activated. However, its properties did not resemble those the light-activated conductance, and thus do not support the hypothesis that Ca²⁺ is sufficient for excitation.Abbreviations BAPTA bis-(o-aminophenoxy)-ethane-N,N,N-tetracetic acid - DBB Di-bromo-bapta - NTA nitrilo-triacetic acid - InsP ₃ inositol 1,4,5-trisphosphate     

Implications of calcium nutrition on the response of Phaseolus vulgaris L. to salinity

The effect of Ca²⁺ level in the growth medium on the response of germination and early seedling growth of Phaseolus vulgaris to NaCl salinity was investigated. When NaCl concentration was increased germination and early seedling growth was decreased. The addition of Ca²⁺ to the media increased both germination percentage and seedling growth. Chloride concentrations were not affected by the level of Ca²⁺. Potassium and Ca²⁺ concentrations and transport from roots to shoots were decreased by NaCl, but were restored by increasing Ca²⁺ in the medium. The opposite was true for Na⁺. Leakage of NO₃ ^- and H₂PO₄ ^- was increased by salinity and reduced by high Ca²⁺ in the medium. The results are discussed in terms of the beneficial effects of calcium for plant growth under saline conditions.     

Ca signalling in exocrine acinar cells: the diffusional properties of cellular inositol 1,4,5-trisphosphate and its role in the release of Ca

The correlation between acetylcholine induced changes in the intracellular free, Ca²⁺ concentration ([Ca²⁺]_i), and the inositol 1,4,5-trisphosphate (Ins(1,4,5)P₃) content in isolated acini from the rat parotid and lacrimal glands was investigated. Applying digital image processing on Fura-2 loaded acini, we observed that Ca²⁺ increases either simultaneously throughout the acinar configurations or that occasionally, the rise near the lumen can precede the rise near the basal part by 50–100 ms. Measurements on cell suspensions revealed a correlation between changes in [Ca²⁺]_i and changes in the cellular Ins(1,4,5)P₃ content, and it is concluded that in the individual cells Ins(1,4,5)P₃ is released to the cytosol within the first second after stimulation. Applying a diffusion coefficient for cytoplasmic Ins(1,4,5)P₃ of 2.83 × 10⁻⁶ cm²/s (Allbritton et al., 1992, Science, 258, 1812–1815), we have calculated the concentration profile for this messenger in a sphere with a radius of 10 μm where Ins(1,4,5)P₃ is released in the center following a monoexponential function with a rate constant of 4 s⁻¹. Assuming that Ins(1,4,5)P₃ concentrations of 1 or 5% of the maximum value is able to release Ca²⁺, we calculated that Ca²⁺ waves can appear at a rate of 100 or 40 μm/s. The present data are consistent with Ins(1,4,5)P₃ being a cellular messenger, that by diffusion, initiates the Ca²⁺ release from the cellular pools within the first fraction of a second.