Ion trap (biology)

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In biology, an ion trap describes the accumulation of substances in cells or cell compartments due to the different solubility of, due to acid-base reactions , electrically charged molecules ( ions ) and the uncharged, neutral substances. Such weak bases are normally concentrated in compartments which react more acidic than the rest of the environment. However, it can also happen that substances in the basic environment, such as breast milk , accumulate; this is sometimes referred to as an “inverse” ion trap.

Ion trap in the vacuole of plant cells

The central vacuole in plant cells has a more acidic environment than the surrounding cytoplasm ( pH value about 5 to 6). Soluble, uncharged substances can penetrate the membrane surrounding the vacuole (the tonoplast ) relatively easily. If the substance within the vacuole is protonated in an acidic environment , the uncharged molecule becomes an ion with a positive electrical charge. Due to the higher polarity of the ion, it can no longer pass through the ( lipophilic ) membrane. This mechanism allows uncharged molecules to flow into the vacuole, but no longer leave it as charged ions, which means that the vacuole acts as a trap. An enrichment by a factor of 1000 is possible via the mechanism until the few uncharged molecules remaining in the acidic environment create a diffusion equilibrium with the environment.

The ion trap mechanism was at times given great importance in living cells in order to accumulate poisonous alkaloids in the vacuole. It is characterized by the fact that it has a non-specific effect and does not require a special ion channel that requires ATP, i.e. it enriches it passively. It is now clear that most of the accumulation processes in the vacuole of plant cells cannot be based on such passive mechanisms.

Traditionally, the ion trap is used for a classic dye reaction with the dye neutral red . Neutral red is uncharged and yellowish in color in the basic and neutral range and turns red in acid as a (positively charged, protonated) cation . The accumulation of the dye molecules in the vacuole gives it an intense color. The dye can thus be used as a living dye, since it is shielded in the vacuole and does not cause the cell to die, even in high concentrations. The reaction can be used, for example, to detect living cells (since the special environment of the central vacuole is only maintained through active transport processes and is quickly equalized in dead cells). It can also be used to test whether the tonoplasts are still intact, for example if cells have been artificially fragmented. The color reaction is also carried out as a simple student experiment in schools. Since the neutral red dye, like acridine orange , which can be used in a very similar way , also fluoresces , the test can also be used for applications such as fluorescence microscopy . It is also possible to test the pH in compartments of living cells.

Ion traps in animal cells and tissues

Similar to the central vacuole of plant cells, the dye neutral red can also passively accumulate and color in the lysosomes , special organelles in animal cells that contain acidic digestive enzymes. The neutral red test is used to test whether the cells are intact and alive.

In addition to cell organelles, cells or entire tissues can act as ion traps in animal organisms, including humans. What is feared is the effect of over-acidic tissue ( acidosis ), for example as a result of an inflammatory reaction, as an ion trap for local anesthetics . The protonated molecules of the anesthetic can then no longer penetrate membranes and can thus accumulate in the extracellular matrix and thus reach locally unhealthy high concentrations. Similarly, a, hypercapnia -mentioned local increase of the acid-acting carbon dioxide -content particularly well perfused tissue acidify selectively in which then accumulate local anesthetics. This can damage nerve cells in the central nervous system. Since the inside of the nerve cells also has a more acidic effect than the surrounding environment due to the sodium ion channels, the substances can also selectively accumulate in nerve cells.

In a reversal of the reaction, some substances, due to the same mechanism, selectively accumulate in the weakly basic breast milk. In the blood plasma, polar molecules present as ions are fixed in the more basic milieu of breast milk. This can lead to infants being exposed to higher doses than the maternal organism.

Individual evidence

  1. ↑ on the mechanism cf. Stefan Trapp (2003): Plant Uptake and Transport Models for Neutral and Ionic Chemicals. Environmental Science and Pollution Research 11:33 doi: 10.1065 / espr2003.08.169
  2. ^ Gudrun Hoffmann-Thoma (2001): The vacuole. Recycling and disposal in the plant cell. Biology in Our Time 31 (5): 313-322.
  3. ↑ Nobukazu Shitan, Kazufumi Yazaki (2013): New Insights into the Transport Mechanisms in Plant vacuoles. International Review of Cell and Molecular Biology 305: 383-434.
  4. ^ Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger - Textbook of Plant Sciences. Springer Spectrum, 37th completely revised & updated edition, Berlin & Heidelberg 2014. ISBN 978-3-642-54434-7 (print); ISBN 978-3-642-54435-4 (eBook), on page 39.
  5. ^ Maria Mulisch, Ulrich Welsch (founded by Benno Romeis ): Romeis - microscopic technology. 19th edition, Springer Spectrum, Berlin and Heidelberg 2015. ISBN 978-3-642-55189-5 . Cape. 4.2.3.5 Enrichment of neutral red in acidic cell compartments (ion trap), on pages 83–84.
  6. ↑ Ion trap - substance transport through the biomembrane teacher training in Baden-Württemberg, competence-oriented teaching: biology, course level.
  7. ^ Sarah Schoor, Shiu-Cheung Lung, Dustin Sigurdson and Simon DX Chuong: Fluorescent Staining of Living Plant Cells. Chapter 9 in Edward Chee Tak Yeung, Claudio Stasolla, Michael John Sumner, Bing Quan Huang (Editors): Plant Microtechniques and Protocols. Springer Cham Heidelberg etc. 2015. ISBN 978-3-319-19943-6 .
  8. ↑ Kenneth M. Hargreaves & Karl Keizer (2002): Local anesthetic failure in endodontics: Mechanisms and Management. Endodontic Topics 1: 26-39.
  9. ↑ Peter H. Tonner, Lutz Hein: Pharmacotherapy in anesthesia and intensive medicine: Basics and clinical concepts. Springer-Verlag, 2011. ISBN 978-3-540-79156-0 . on page 171.
  10. Jump up ↑ Niels Eijkelkamp, ​​John E. Linley, Mark D. Baker, Michael S. Minett, Roman Cregg, Robert Werdehausen, François Rugiero, John N. Wood (2012): Neurological perspectives on voltage-gated sodium channels. Brain 135 (9): 2585-2612. doi: 10.1093 / brain / aws225 (open access)
  11. Jump up ↑ Arturo Anadón, Maria Rosa Martínez-Larrañaga, Eva Ramos, Victor Castellano: Transfer of drugs and xenobiotics through milk. Chapter 6 in Ramesh C. Gupta (editor): Reproductive and Developmental Toxicology. Elsevier, Amsterdam etc. 2011. ISBN 978-0-12-382032-7 doi: 10.1016 / B978-0-12-382032-7.10006-2