Sub-second quenched-flow/X-ray microanalysis shows rapid Ca2+ mobilization from cortical stores paralleled by Ca2+ influx during synchronous exocytosis in Paramecium cells

Hardt, Martin; Plattner, Helmut

Sub-second quenched-flow/X-ray microanalysis shows rapid Ca2+ mobilization from cortical stores paralleled by Ca2+ influx during synchronous exocytosis in Paramecium cells

Dateien

Sub_second_quenched_flow.pdfGröße: 545.81 KBDownloads: 306

Datum

2000

Autor:innen

Hardt, Martin

Plattner, Helmut

Projekt

Funktionell-ultrastrukturelle Analyse des Exocytose-Prozesses (Sekretausschleusung)

Sammlungen

Biologie

Publikationstyp

Zeitschriftenartikel

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European Journal of Cell Biology. 2000, 79(200), pp. 642-652. ISSN 0171-9335. Available under: doi: 10.1078/0171-9335-00087

Zusammenfassung

Though only actual local free Ca2+ concentrations, [Ca2+], rather than total Ca concentrations, [Ca], govern cellular responses, analysis of total calcium fluxes would be important to fully understand the very complex Ca2+ dynamics during cell stimulation. Using Paramecium cells we analyzed Ca2+ mobilization from cortical stores during synchronous (¡Ü80 ms) exocytosis stimulation, by quenched-flow/cryofixation, freeze-substitution (modified for Ca retention) and X-ray microanalysis which registers total calcium concentrations, [Ca]. When the extracellular free calcium concentration, [Ca2+]e, is adjusted to 30 nM, i.e. slightly below the normal free intracellular calcium concentration, [Ca2+]i=65 nM, exocytosis stimulation causes release of 52% of calcium from stores within 80 ms. At higher extracellular calcium concentration, [Ca2+]e=500 ¦ÌM, Ca2+ release is counterbalanced by influx into stores within the first 80 ms, followed by decline of total calcium, [Ca], in stores to 21% of basal values within 1 s. This includes the time required for endocytosis coupling (350 ms), another Ca2+-dependent process. To confirm that Ca2+ mobilization from stores is superimposed by rapid Ca2+ influx and/or uptake into stores, we substituted Sr2+ for Ca2+ in the medium for 500 ms, followed by 80 ms stimulation. This reveals reduced Ca signals, but strong Sr signals in stores. During stimulation, Ca2+ is spilled over preformed exocytosis sites, particularly with increasing extracellular free calcium, [Ca2+]e. Cortically enriched mitochondria rapidly gain Ca signals during stimulation. Balance calculations indicate that total Ca2+ flux largely exceeds values of intracellular free calcium concentrations locally required for exocytosis (as determined previously). Our approach and some of our findings appear relevant also for some other secretory systems.

Fachgebiet (DDC)

570 Biowissenschaften, Biologie

Schlagwörter

Calcium, exocytosis, microanalysis, Paramecium, secretion

Zitieren

ISO 690

HARDT, Martin, Helmut PLATTNER, 2000. Sub-second quenched-flow/X-ray microanalysis shows rapid Ca2+ mobilization from cortical stores paralleled by Ca2+ influx during synchronous exocytosis in Paramecium cells. In: European Journal of Cell Biology. 2000, 79(200), pp. 642-652. ISSN 0171-9335. Available under: doi: 10.1078/0171-9335-00087

BibTex

@article{Hardt2000Subse-7889,
  year={2000},
  doi={10.1078/0171-9335-00087},
  title={Sub-second quenched-flow/X-ray microanalysis shows rapid Ca2+ mobilization from cortical stores paralleled by Ca2+ influx during synchronous exocytosis in Paramecium cells},
  number={200},
  volume={79},
  issn={0171-9335},
  journal={European Journal of Cell Biology},
  pages={642--652},
  author={Hardt, Martin and Plattner, Helmut}
}

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