sq-23377 and lanthanum-chloride

Carrot callus was centrifuged at 10 g and compared to callus growing at 1 g on agar in the presence of increasing sodium chloride concentrations. Growth after 14 days was enhanced in the centrifuged samples versus samples kept at 1 g. This effect was not found when the samples were grown on potassium chloride. At 50 mM NaCl, the calcium ionophore ionomycin was applied to centrifuged and noncentrifuged callus samples. In both experiments, the growth of callus increased with increasing ionomycin concentrations but under 10 g this increase was more enhanced. As inhibitors of calcium influx, lanthanum and gadolinium chloride were chosen in the presence of 50 mM NaCl. Both inhibitors inhibited growth at 1 g at low concentrations of around 2 microM, whereas the centrifuged samples were not or much less so inhibited. We tested an involvement of actin by application of cytochalasin D to callus grown in the presence of 50 mM NaCl. In both types of samples, growth at 1 g and growth at 10 g, cytochalasin D enhanced growth but the effect was clearly stronger at 10 g than at 1 g. As increased halotolerance was only observed in the presence of increased sodium ions, not potassium ions, and as halotolerance is known to be induced by an influx of calcium, the data suggest that a calcium influx induced by hypergravity and possibly modulated by actin caused the observed increase in halotolerance at 10 g.

Topics: Actin Cytoskeleton; Adaptation, Physiological; Calcium Signaling; Centrifugation; Chlorides; Cytochalasin D; Daucus carota; Dose-Response Relationship, Drug; Gadolinium; Gravity Sensing; Hypergravity; Ionomycin; Ionophores; Lanthanum; Mechanotransduction, Cellular; Potassium Chloride; Sodium Chloride

In human platelets and other non-excitable cell types depletion of the intracellular calcium stores promotes calcium entry across the plasma membrane. Although the mechanism of this store-mediated calcium entry remains uncertain, it has been suggested that a tyrosine phosphorylation step could be involved. In support of this hypothesis various tyrosine kinase inhibitors have been shown to reduce store-mediated calcium entry in platelets, although this inhibition is never complete. Here we investigate the properties of store-mediated calcium entry in human platelets during the time course of its activation. Our data suggest that at least two pathways may contribute to store-mediated calcium entry in these cells. An early component, activated soon after the initiation of Ca2+ store depletion, is insensitive to trivalent cations, SKF 96365 and tyrosine kinase inhibitors. This is followed by a second component which is inhibited by La3+, SKF 96365 and by tyrosine kinase inhibitors. These results suggest a role for tyrosine kinases in generating only the later stages of store-mediated calcium entry in platelets and may explain the incomplete inhibition of this pathway by inhibitors of tyrosine kinases.

Topics: Androstadienes; Biological Transport; Blood Platelets; Calcium; Calcium Channel Blockers; Calcium Signaling; Chelating Agents; Econazole; Egtazic Acid; Enzyme Inhibitors; Humans; Imidazoles; Ionomycin; Ionophores; Lanthanum; Manganese; Phosphorylation; Protein-Tyrosine Kinases; Thapsigargin; Tyrosine; Wortmannin

In fura-2-loaded bovine adrenal chromaffin cells, 0.5 microM angiotensin II (AII) stimulated a 185 +/- 19 nM increase of intracellular-free calcium [( Ca2+]i) approximately 3 s after addition. The time from the onset of the response until achieving 50% recovery (t 1/2) was 67 +/- 10 s. Concomitantly, AII stimulated both the release of 45Ca2+ from prelabeled cells, and a 4-5-fold increase of [3H]inositol 1,4,5-trisphosphate [( 3H]Ins(1,4,5)P3) levels. In the presence of 50 microM LaCl3, or when extracellular-free Ca2+ [( Ca2+]o) was less than 100 nM, AII still rapidly increased [Ca2+]i by 95-135 nM, but the t 1/2 for recovery was then only 23-27 s. In medium with 1 mM MnCl2 present, AII also stimulated a small amount of Mn2+ influx, as judged by quenching of the fura-2 signal. When [Ca2+]o was normal (1.1 mM) or low (less than 60 nM), 1-2 microM ionomycin caused [Ca2+]i to increase 204 +/- 26 nM, while also releasing 45-55% of bound 45Ca2+. With low [Ca2+]o, ionomycin pretreatment abolished both the [Ca2+]i increase and 45Ca2+ release stimulated by AII. However, after ionomycin pretreatment in normal medium, AII produced a La3+-inhibitable increase of [Ca2+]i (103 +/- 13 nM) with a t 1/2 of 89 +/- 8 s, but no 45Ca2+ release. No pretreatment condition altered AII-induced formation of [3H]Ins(1,4,5)P3. We conclude that AII increased [Ca2+]i via rapid and transient Ca2+ mobilization from Ins(1,4,5)P3- and ionomycin-sensitive stores, accompanied (and/or followed) by Ca2+ entry through a La3+-inhibitable divalent cation pathway. Furthermore, the ability of AII to activate Ca2+ entry in the absence of Ca2+ mobilization (i.e. after ionomycin pretreatment) suggests a receptor-linked stimulus other than Ca2+ mobilization initiates Ca2+ entry.

Topics: Adrenal Glands; Angiotensin II; Animals; Calcium; Calcium Radioisotopes; Cations, Divalent; Cattle; Chlorides; Chromaffin System; Egtazic Acid; Extracellular Space; Inositol 1,4,5-Trisphosphate; Intracellular Fluid; Ionomycin; Lanthanum; Manganese; Manganese Compounds; Spectrometry, Fluorescence