1887

Abstract

Cells of the cyanobacterium sp. PCC 6803 are equipped with a mechanosensitive ion channel MscL that is located in their plasma membrane. However, the exact function of the channel in this freshwater cyanobacterium is unknown. This study shows that cells of are capable of releasing Ca in response to depolarization of the plasma membrane by the K ionophore valinomycin in the presence of K or by tetraphenylphosphonium (TPP). A fluorescent dye, diS-C-(5), sensitive to membrane potential and the metallochromic Ca indicator arsenazo III were used to follow the plasma membrane depolarization and the Ca release, respectively. The Ca release from wild-type cells was temperature-dependent and it was strongly inhibited by the Ca channel blocker verapamil and by the mechanosensitive channel blocker amiloride. In MscL-deficient cells, Ca release was about 50 % of that from the wild-type cells. The mutant cells had lost temperature sensitivity of Ca release completely. However, verapamil and amiloride inhibited Ca release from these cells in same manner as in the wild-type cells. This suggests the existence of additional Ca transporters in , probably of a mechanosensitive nature. Evidence for the putative presence of intracellular Ca stores in the cells was obtained by following the increase in fluorescence intensity of the Ca indicator chlortetracycline. These results suggest that the MscL of might operate as a verapamil/amiloride-sensitive outward Ca channel that is involved in the plasma-membrane depolarization-induced Ca release from the cells under temperature stress conditions.

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2003-05-01
2020-04-10
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