Localisation of intracellular calcium stores in the striated muscles of the jellyfish Polyorchis penicillatus: possible involvement in excitation-contraction coupling.
When jellyfish striated muscles were stimulated directly, the amplitude of contractile tension increased as the stimulation frequency increased. Application of 10 mmol l(-1) caffeine reduced the amplitude of contractile tension and abolished this facilitatory relationship, indicating that calcium stores participate in excitation-contraction 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 excitation-contraction coupling.
Lin
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Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9.
Spencer
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D000818:Animals; D002118:Calcium / Q000032:analysis* / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000032:analysis; D011232:Chemical Precipitation; D004558:Electric Stimulation; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000737:chemistry* / Q000502:physiology* / Q000648:ultrastructure; D011192:Potassium Dichromate; D012508:Sarcolemma / Q000737:chemistry; D037401:Scyphozoa
D000252:Calcium-Transporting ATPases; D002118:Calcium; D011192:Potassium Dichromate