Mechanisms associated with the negative inotropic effect of deuterium oxide in single rat ventricular myocytes.
Deuterium oxide (D2O) is known to cause a negative inotropic effect in muscle although the mechanisms associated with this response in cardiac muscle are not well understood. We studied the effects of D2O in single rat ventricular myocytes in order to characterise the mechanisms associated with its negative inotropic effect and to assess its possible use as an acute modulator of microtubules. D2O rapidly reduced the magnitude of contraction in rat ventricular myocytes, and there was some recovery of contraction in the presence of D2O. Colchicine, an agent known to depolymerise microtubules, did not modify the effect of D2O. D2O decreased the L-type Ca2+ current (ICa), measured under whole cell and perforated patch clamp conditions. Slowing of the time to peak and a delay in inactivation of ICa were observed. Intracellular calcium ([Ca2+]i) and sodium ([Na+]i) were measured using the fluorescent indicators fura-2 and SBFI, respectively. The fall in contraction upon exposure to D2O was not associated with a fall in the [Ca2+]i transient; this response is indicative of a reduction in myofilament Ca2+ sensitivity. Both the [Ca2+]i transient and [Na+]i increased during the partial recovery of contraction in the presence of D2O. We conclude that a decrease in the myofilament sensitivity for Ca2+ and a reduction in Ca2+ influx via ICa are principally responsible for the negative inotropic effect of D2O in cardiac muscle. We found no evidence to explain the negative inotropic effect of D2O in terms of microtubule proliferation. In addition we suggest that acute application of D2O is not a useful procedure for the investigation of the role of microtubules in excitation-contraction coupling in cardiac muscle.
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School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK and Laboratoire de Physiologie des cellules Cardiaques et Vasculaires, CNRS, UMR 6542, Faculte des Sciences, Tours 37200, France.
Brette
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Haroon
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White
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D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000502:physiology; D002469:Cell Separation; D017666:Deuterium Oxide / Q000494:pharmacology*; D004553:Electric Conductivity; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D016257:Fura-2; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D008870:Microtubules / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology; D009994:Osmolar Concentration; D051381:Rats; D012964:Sodium / Q000378:metabolism; D016276:Ventricular Function / Q000187:drug effects*
D001572:Benzofurans; D020746:Calcium Channels, L-Type; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; C061665:sodium-binding benzofuran isophthalate; D012964:Sodium; D017666:Deuterium Oxide; D002118:Calcium; D016257:Fura-2