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Localisation of intracellular calcium stores in the striated muscles of the jellyfish Polyorchis penicillatus: possible involvement in excitationcontraction coupling
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9 and Bamfield Marine Station, Bamfield, British Columbia, Canada V1R 1B
*Author for correspondence (e-mail: aspencer{at}bms.bc.ca)
Accepted July 31, 2001
When jellyfish striated muscles were stimulated directly, the amplitude of contractile tension increased as the stimulation frequency increased. Application of 10 mmol l1 caffeine reduced the amplitude of contractile tension and abolished this facilitatory relationship, indicating that calcium stores participate in excitationcontraction coupling. Calcium stores were identified ultrastructurally using enzymatic histochemistry to localize CaATPases, and potassium dichromate to precipitate calcium. Electron energy-loss spectroscopy was used to verify the presence of calcium in precipitates. Both CaATPase and calcium were localised in membrane-bound vesicles beneath the sarcolemma. We concluded that sub-sarcolemmal vesicles could act as calcium stores and participate in excitationcontraction coupling.
Key words: calcium stores, excitationcontraction coupling, jellyfish, Polyorchis penicillatus, caffeine, CaATPase.
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