The oppositely directed Ca2+ and Na+ transmembrane transport in algal cells |
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Authors: | Fatima G. Karimova Ekaterina E. Kortchouganova Igor A. Tarchevsky Madina R. Iagoucheva |
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Affiliation: | (1) Laboratory of Protein Metabolism, Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, Kazan |
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Abstract: | Summary The countertransport of Ca2+ and Na+ across the membranes of the unicellular fresh-water algaChlamydomonas reinhardtii CW-15 and twoDunaliella species differing in salt tolerance was studied. All algae used are devoid of cell walls. The calcium uptake by twoDunaliella species depended markedly on the intracellular sodium concentration. This calcium uptake was accompanied by Na+ release. For 15 and 30 s after artificial gradient formation (Naint+ greater than Naext+) the ratio of released Na+ to absorbed Ca2+ was 31 and 41, respectively. For the extremely halotolerantD. salina, the apparent Michaelis constant of the Ca2+ uptake was 33 M, and for the marine halotolerant algaD. maritima, it was equal to 400 M, presuming more efficient Na+-for-Ca2+ exchange inD. salina cells. Ouabain, an inhibitor of Na+/K+-ATPase, suppressed Na+ transfer by 25%, whereas the agents blocking Ca2+-channels did not affect the transport of Ca2+ and Na+. The oppositely directed transmembrane Ca2+ and Na+ transfer was shown to depend on the external concentrations of Na+ and H+. In the fresh-water algaC. reinhardtii CW-15 (Naext+ greater than Naint+), the direction of Ca2+ and Na+ fluxes across the plasma membrane was opposite to those described for Dunaliella cells. The results obtained point to the ability of the Na+-Ca2+ exchanger function in plasma membranes of algal cells. |
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Keywords: | Dunaliella Calcium Sodium Transport Na+-Ca2+ exchanger Algae |
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