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Cardiovascular Research 1995 30(3):357-362; doi:10.1016/S0008-6363(95)00053-4
© 1995 by European Society of Cardiology
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Copyright © 1995, European Society of Cardiology

Effects of thapsigargin on aequorin-injected and skinned preparations of ferret ventricular muscles

Tadashi Tanaka*, Kimiaki Komukai, Makoto Kawai, Etsuko Tanaka and Satoshi Kurihara

Department of Physiology, The Jikei University School of Medicine, 3-25-8 Nishishinbashi, Minato-ku, Tokyo 105, Japan

* Corresponding author. (+3)3433-1111, ext. 2221.

Objective: We investigated the effects of thapsigargin (TG) (0.1–1 µM) on the relation between intracellular Ca2+ concentration and tension in ferret papillary muscles using aequorin-injected and skinned preparations. Methods: Aequorin was injected into the superficial cells of ferret papillary muscles; the Ca2+ signals of aequorin and tension in twitch and those with the application of 15 mM caffeine were simultaneously measured. The alteration of Ca2+ sensitivity of the contractile elements was examined by measuring the pCa-tension relation in Triton-X-treated skinned preparations. Results: TG decreased the peak of the Ca2+ signal accompanied by a prolonged decay time. However, the tension was scarcely altered even at 1 µM TG. TG inhibited the caffeine-induced Ca2+ signal. Prolongation of decay of the Ca2+ signal by TG in twitch was further enhanced by isoprenaline (10 nM). The pCa-tension relation of the skinned preparation was slightly but significantly shifted to the right by TG. Conclusions: The apparent dissociation of the effects of TG on the Ca2+ signal and tension in intact preparations is not a result of alteration of the Ca2+ sensitivity of the myofilaments. The effects of TG in multicellular preparations are probably limited to the outer layer of the preparation. The slower time course of the Ca2+ signal induced by TG is due to the inhibition of Ca2+ uptake by sarcoplasmic reticulum, which is more significantly observed when the intracellular Ca2+ transient is increased by isoprenaline.

KEYWORDS Calcium sensitivity; Calcium transients; Contractile function; Catecholamines; Thapsigargin; Caffeine; Ferret ventricle


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