The effects of caffeine on sodium transport, membrane potential, mechanical tension and ultrastructure in barnacle muscle fibres

• Published in: The Journal of physiology 1974-10, Vol.242 (1), p.1-34
• Main Authors: Bittar, E. Edward, Hift, Helen, Huddart, Henry, Tong, Edmund
• Format: Article
• Language: English
• Subjects: Acetates - pharmacology; Animals; Arthropoda; Biological Transport, Active - drug effects; Caffeine - antagonists & inhibitors; Caffeine - pharmacology; Calcium - pharmacology; Calcium Chloride - pharmacology; Chelating Agents - pharmacology; Cyclic AMP - pharmacology; Cyclic GMP - pharmacology; Dose-Response Relationship, Drug; Glycols - pharmacology; Hydrogen-Ion Concentration; In Vitro Techniques; Membrane Potentials - drug effects; Microscopy, Electron; Muscle Contraction - drug effects; Myofibrils - drug effects; Myofibrils - ultrastructure; Ouabain - pharmacology; Phenytoin - pharmacology; Phosphoric Diester Hydrolases - pharmacology; Procaine - pharmacology; Sodium - metabolism; Stimulation, Chemical; Thoracica - physiology
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/jphysiol.1974.sp010691

1. The effects of graded concentrations of caffeine on the Na efflux were investigated. External application of 10 m M caffeine usually caused a biphasic response, viz. a fall, followed by a rise in the Na efflux. 1 and 5 m M caffeine usually caused stimulation. Only the stimulatory phase of this response depended on the presence of external Ca 2+ . 2. Internal application of 100 m M caffeine caused a small rise in the Na efflux, the magnitude of which was independent of external Ca 2+ and comparable to that obtained with external application of 1 m M caffeine. This action, however, could be greatly augmented by pre-treating the fibre with 5 × 10 -5 M ouabain. 3. The rise in Na efflux caused by external application of 10 m M caffeine could be greatly augmented by pre-treating the fibre with 5 × 10 -5 M ouabain. The observed stimulatory response was biphasic, more so in the absence of external Ca 2+ . Restoration of external Ca 2+ following the onset of the second stimulatory phase resulted in further rise of the Na efflux. Measurements of the Na efflux during treatment with graded concentrations of ouabain and 10 m M caffeine showed that the rate coefficient for Na efflux varied with the ouabain concentration in the range 10 -8 -10 -4 M . Measurements of the ouabain-insensitive Na efflux before and during treatment with 10 m M caffeine in bathing media containing varying concentrations of Ca, disclosed the existence of two Ca 2+ -thresholds, one in the 0-2·5 m M range and the other in the 12·5-15 m M range. 4. Comparisons were made between the effects on the Na efflux of 10 m M caffeine followed by external acidification, and external acidification, followed by 10 m M caffeine. The magnitude of the response of the ouabain-insensitive Na efflux to external acidification before treatment with 10 m M caffeine was greater than that found when external acidification followed external application of the alkaloid. It also was considerably greater than that of the response to external application of 10 m M caffeine before external acidification. 5. External application of 10 m M procaine prevented 10 m M caffeine from stimulating the Na efflux, and from inducing contractures. Internal application of 100 m M -EGTA reduced the response of the Na efflux to 10 m M caffeine, and also prevented the fibre from contracting. External application of 10 -4 M diphenylhydantoin reduced the response of the Na efflux to 10 m M caffeine but failed to prevent the development o