Excitation-contraction coupling in cardiac Purkinje fibers. Effects of caffeine on the intracellular [Ca2+] transient, membrane currents, and contraction.
Open Access
- 1 March 1984
- journal article
- research article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 83 (3), 417-433
- https://doi.org/10.1085/jgp.83.3.417
Abstract
The effects of caffeine on tension, membrane potential, membrane currents, and intracellular [Ca2+], measured as the light emitted by the Ca2+-activated photoprotein aequorin, were studied in canine cardiac Purkinje fibers. An initial, transient, positive inotropic effect of caffeine was accompanied by a transient increase in the second component of the aequorin signal (L2) but not the first (L1). In the steady state, 4 or 10 mM caffeine always decreased twitch tension and greatly reduced both L1 and L2. At a concentration of 2 mM, caffeine usually reduced but occasionally increased the steady state twitch tension. However, 2 mM caffeine always reduced both L1 and L2. Caffeine eliminated the diastolic oscillations of intracellular [Ca2+] induced by high extracellular [Ca2+]. In voltage-clamp experiments, 10 mM caffeine reduced the transient outward current and the peak tension elicited by step depolarization from a holding potential of -45 mV. In the presence of 20 mM Cs+, 10 mM caffeine reduced slow inward current. However, the time course of this reduction was far slower than that in tension and light observed in separate experiments. The simplest explanation of the results is that caffeine inhibits the sequestration of Ca2+ by the sarcoplasmic reticulum. The results also suggest that in Purkinje fibers caffeine increases the sensitivity of the myofilaments to Ca2+.This publication has 38 references indexed in Scilit:
- Excitation-contraction coupling in cardiac Purkinje fibers. Effects of cardiotonic steroids on the intracellular [Ca2+] transient, membrane potential, and contraction.The Journal of general physiology, 1984
- Analysis of caffeine action in single trabeculae of the frog heartProceedings of the Royal Society of London. B. Biological Sciences, 1981
- Calcium Transients During Excitation-Contraction Coupling in Mammalian Heart: Aequorin Signals of Canine Purkinje FibersScience, 1980
- Influence of chloride, potassium, and tetraethylammonium on the early outward current of sheep cardiac Purkinje fibers.The Journal of general physiology, 1979
- Interaction between Caffeine and Adenosine on the Membrane Current and Tension Component in the Bullfrog Atrial MuscleThe Japanese Journal of Physiology, 1979
- Inactivation without facilitation of calcium conductance in caesium-loaded neurones of AplysiaNature, 1978
- CALCIUM‐INDUCED RELEASE OF CALCIUM FROM THE SARCOPLASMIC RETICULUM OF SKINNED CELLS FROM ADULT HUMAN, DOG, CAT, RABBIT, RAT, AND FROG HEARTS AND FROM FETAL AND NEW‐BORN RAT VENTRICLES*Annals of the New York Academy of Sciences, 1978
- Role of intracellular calcium in the transient outward current of calf Purkinje fibresNature, 1977
- Excitation-Contraction Coupling of Isolated Cardiac Fibers with Disrupted or Closed Sarcolemmas: CALCIUM-DEPENDENT CYCLIC AND TONIC CONTRACTIONSCirculation Research, 1972
- EFFECTS OF CAFFEINE ON THE MEMBRANE POTENTIALS AND CONTRACTILITY OF THE GUINEA PIG ATRIUMThe Japanese Journal of Physiology, 1972