| Summary: | An internodal cell of Nitella flexilis treated with 10 mM KC1 was vacuole-perfused with an isotonic solution containing ethyleneglycol-bis-(rβ-aminoethylether) N,N,N,N -tetraacetic acid (EGTA) and its content including cytoplasm was squeezed out into a vessel and covered with silicone oil. When the hypotonic solution was added into the cytoplasmic drop which had been mixed with aequorin, a significant increase in the light emission from aequorin was detected with the photomultiplier, indicating a release of Ca2+ from some cell organdies storing Ca2+. This increase in the light emission was strongly inhibited by treating cells with 0.1 mM HgCl 2 which is known to inhibit water channels in the plasma membrane. The inhibition was completely recovered by washing HgCl 2 with 2-mer-captoethanol. This suggests that water channels may exist in the membrane of Ca2+ stores and play an essential role in the hydration-induced Ca2+ release.
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