title: Effects of quinine on the isometric tension and intracellular calcium movements in single giant muscle fibres.
abstract: The effects of the alkaloid quinine on the tension response and intracellular calcium movements of giant muscle fibres are reported. Under voltage clamp conditions, the isometric tension showed an early transient increase (approx. 1.6 fold), and a subsequent decline to negligible values in response to a constant step depolarization. At rest and under voltage clamp condition, fibres injected with the Ca-indicator aequorine showed a 40% increase in aequorine light output, while no change was observed in tension response. We interpret these results as due to the calcium releasing action of quinine both on the SR membrane, and at the diadic level where calcium ions are crucial for the E-C coupling process.
mesh_terms: D000331:Aequorin / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D007537:Isometric Contraction; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction; D009132:Muscles / Q000187:drug effects* / Q000378:metabolism; D011803:Quinine / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D001468:Thoracica / Q000502:physiology*
chemical_list: D007473:Ion Channels; D000331:Aequorin; D011803:Quinine; D002118:Calcium