Mechanosensitive Ca2+ release from intracellular stores in Nitella flexilis.
We found previously that the cytoplasmic drop isolated from internodal cells of Nitella flexilis releases Ca2+ in response to hypotonic treatment and named the phenomenon hydration-induced Ca2+ release (HICR). The HICR is assumed to be a result of activation of Ca2+ permeable channels in the membrane of Ca2+ stores in a stretch-activated manner. To prove this idea, mechanical stimulus was applied to the drop by means of shooting isotonic/hypnotic medium or silicon oil into the drop, or compressing the drop. All these mechanical stimuli induced a rapid increase in the Ca2+ concentration of the drop. The chloroplast fraction isolated from the cytoplasmic drop released Ca2+ on compression, while the chloroplast-free cytoplasm did not. In Chara corallina, the cytoplasmic drop, which shows a very weak HICR, also responded weakly to the mechanical stimulus, but the chloroplast fraction was inert. When chloroplasts from Chara were added to the chloroplast-free cytoplasm of N. flexilis, the cytoplasm recovered the mechanoresponse. Starch grains were as effective as chloroplasts. The data indicate that Ca2+ permeable channels in the membrane of Ca2+ stores in N. flexilis are really mechano-sensitive.
Kikuyama
M
M
Biological Laboratory, The University of the Air, 2-11 Wakaba, Mihama-ku, Chiba, 261-8586 Japan.
Tazawa
M
M
D002118:Calcium / Q000378:metabolism*; D000460:Chlorophyta / Q000502:physiology*; D002736:Chloroplasts / Q000187:drug effects / Q000502:physiology; D003593:Cytoplasm / Q000502:physiology; D007038:Hypotonic Solutions / Q000494:pharmacology; D007424:Intracellular Fluid / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology
D007038:Hypotonic Solutions; D002118:Calcium