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The effects of La3+ and charged amphiphiles on sarcolemma-bound Ca2+ in isolated cardiomyocytes
J Mol Cell Cardiol 19 (Supplement III) (1987)
310
Ca2+-ENTRY BLOCKERS PROTECT AGAINST OUABAIN-INDUCED SHAPE CHANGES IN ISOLATED CARDIOMYOCYTES. L. Ver Donck, G. Vandeplassche, M. Borgers. Laboratory of Cell Biology, Department of Life Sciences, Janssen Pharmaceutiea Research Laboratories, B-2340 Beerse, BelEium. Cardiac ~lycoside intoxication has been suEgested to be caused by intracellular Ca2+-accumulation (Ca2+-overload). We investiEated the degenerative chanEes induced by toxic doses of ouabain on electrically paced isolated cardiomyoeytes and the effects of various Ca2+-entry blockers. Cardiomyocytes displayed vigorous synchronous contractions resultinE in hypercontracture of all cells within 20 min after ouabain addition. The time course of cellular shape chanEes could be influenced by varyinE the ouabain concentration, the extracellular Ca 2+concentration and the pacing frequency. Flunarizine, cinnarizine and R 56 865 afforded considerable protection. The slow channel blockers verapamil, nicardipine and nifedipine were also protective. The latter drugs however interfered stronEly with the electrical excitability of cardiomyocytes, suEgestin E that their neEative inotropic effect is responsible for the protection. Cinnarizine, flunarizine and R 56 865, on the other hand, have no inotropic effects and allow normal excitability of cardiomyocytes. These 'results suEEest that Ca2+-entry blockers with no affinity for the slow channels protect aEainst ouabain-intoxication by preventinE intracellular Ca2+-overload without a loss in cardiac centractiliy.
311
THE EFFECTS OF La 3+ AND CHARGED ~d~PHIPHILES ON SARCOLEf~A-BOUND Ca 2+ IN ISOLATED CARDIOMYOCYTES. L. Vet Donck, G. Vandeplassche, M. Borgers. Laboratory of Cell Biology, Department of Life Sciences, Janssen Pharmaceutica Research Laboratories, B-2340 Beerse, Belgium. A large fraction of the rapidly exchangeable component of cellular Ca 2+ important in control of myocardial force development, has been shown by Langer and c o - w o r k e ~ 0 be bound to sarcolemmal sites : La 3+, cationic and anionic amphiphiles were shown to modulate force development and sarcolemmal Ca2+-binding. We investigated the effects of La 3+ and charged amphiphiles on cytochemically demonstrable sarcolemma-bound Ca2+-pools in cardiomyocytes (PPA : phosphate-pyroantimonate method). Control cells displayed 20 nm thick electrondense particles, representing Ca 2+, which were exclusively confined to the sarcolemmal bilayer, sarcolemmal vesicles, T-tubuli and gap-junctions, similar as in intact cardiac tissue. Cardiomyocytes incubated with 1 mM LaCl 3 lost all precipitate. When cells were incubated with the anionic amphiphiles dodecylsulphate or phospholipase D, sarcolemmal Ca2+-binding was largely preserved. Incubation with the cationic amphiphiles polymyxin B or dodecyltrimethylamine resulted in loss of sarcolemma-bound Ca 2+ and induced shape changes of cardiomyocytes. These results suggest that the cytochemically displayed and La3+-displacable sarcolemma-associated Ca 2+ might be identical to the pool that possibly participates in excitation-contraction coupling.
312 RESPONSES TO I SOPRENALI NE AND CALCIUM I N MYOCYTES I SOLATED FROM THE HEARTS OF ADRIAMYCIN-TREATED RABBITS. G. Vescovo, M.S. Kirby, S.E. Harding, R.B. Wanless, I.S. Anand, P.A. Poole-Wilson. The Cardiothoracic Institute, 2, BeaumontStreet, London, W] N 2DX, England. Rabbits were given 1 mg/kg adriamycin i.v. twice weekly for 7 weeks. Haemodynamic measurements on conscious animals showed that cardiac failure was produced by this procedure. Myocytes were isolated from the hearts of control and adriamycin-treated rabbits. Measurementsof contraction of superfused, electrically-stimulated cells were made using a video camera and edge-detection monitor. Contraction amplitude and rate of change of sarcomere length in 1ram calcium did not differ between control and adriamycin-treated groups. In 8mM calcium, sarcomere shortening of cells fi'om adrlamycin-treated animals was 0.199 +- 0.016 (n=7), significantly less than the 0.255+0.013 (n=7) of controls (p
S.104
310
Ca2+-ENTRY BLOCKERS PROTECT AGAINST OUABAIN-INDUCED SHAPE CHANGES IN ISOLATED CARDIOMYOCYTES. L. Ver Donck, G. Vandeplassche, M. Borgers. Laboratory of Cell Biology, Department of Life Sciences, Janssen Pharmaceutiea Research Laboratories, B-2340 Beerse, BelEium. Cardiac ~lycoside intoxication has been suEgested to be caused by intracellular Ca2+-accumulation (Ca2+-overload). We investiEated the degenerative chanEes induced by toxic doses of ouabain on electrically paced isolated cardiomyoeytes and the effects of various Ca2+-entry blockers. Cardiomyocytes displayed vigorous synchronous contractions resultinE in hypercontracture of all cells within 20 min after ouabain addition. The time course of cellular shape chanEes could be influenced by varyinE the ouabain concentration, the extracellular Ca 2+concentration and the pacing frequency. Flunarizine, cinnarizine and R 56 865 afforded considerable protection. The slow channel blockers verapamil, nicardipine and nifedipine were also protective. The latter drugs however interfered stronEly with the electrical excitability of cardiomyocytes, suEgestin E that their neEative inotropic effect is responsible for the protection. Cinnarizine, flunarizine and R 56 865, on the other hand, have no inotropic effects and allow normal excitability of cardiomyocytes. These 'results suEEest that Ca2+-entry blockers with no affinity for the slow channels protect aEainst ouabain-intoxication by preventinE intracellular Ca2+-overload without a loss in cardiac centractiliy.
311
THE EFFECTS OF La 3+ AND CHARGED ~d~PHIPHILES ON SARCOLEf~A-BOUND Ca 2+ IN ISOLATED CARDIOMYOCYTES. L. Vet Donck, G. Vandeplassche, M. Borgers. Laboratory of Cell Biology, Department of Life Sciences, Janssen Pharmaceutica Research Laboratories, B-2340 Beerse, Belgium. A large fraction of the rapidly exchangeable component of cellular Ca 2+ important in control of myocardial force development, has been shown by Langer and c o - w o r k e ~ 0 be bound to sarcolemmal sites : La 3+, cationic and anionic amphiphiles were shown to modulate force development and sarcolemmal Ca2+-binding. We investigated the effects of La 3+ and charged amphiphiles on cytochemically demonstrable sarcolemma-bound Ca2+-pools in cardiomyocytes (PPA : phosphate-pyroantimonate method). Control cells displayed 20 nm thick electrondense particles, representing Ca 2+, which were exclusively confined to the sarcolemmal bilayer, sarcolemmal vesicles, T-tubuli and gap-junctions, similar as in intact cardiac tissue. Cardiomyocytes incubated with 1 mM LaCl 3 lost all precipitate. When cells were incubated with the anionic amphiphiles dodecylsulphate or phospholipase D, sarcolemmal Ca2+-binding was largely preserved. Incubation with the cationic amphiphiles polymyxin B or dodecyltrimethylamine resulted in loss of sarcolemma-bound Ca 2+ and induced shape changes of cardiomyocytes. These results suggest that the cytochemically displayed and La3+-displacable sarcolemma-associated Ca 2+ might be identical to the pool that possibly participates in excitation-contraction coupling.
312 RESPONSES TO I SOPRENALI NE AND CALCIUM I N MYOCYTES I SOLATED FROM THE HEARTS OF ADRIAMYCIN-TREATED RABBITS. G. Vescovo, M.S. Kirby, S.E. Harding, R.B. Wanless, I.S. Anand, P.A. Poole-Wilson. The Cardiothoracic Institute, 2, BeaumontStreet, London, W] N 2DX, England. Rabbits were given 1 mg/kg adriamycin i.v. twice weekly for 7 weeks. Haemodynamic measurements on conscious animals showed that cardiac failure was produced by this procedure. Myocytes were isolated from the hearts of control and adriamycin-treated rabbits. Measurementsof contraction of superfused, electrically-stimulated cells were made using a video camera and edge-detection monitor. Contraction amplitude and rate of change of sarcomere length in 1ram calcium did not differ between control and adriamycin-treated groups. In 8mM calcium, sarcomere shortening of cells fi'om adrlamycin-treated animals was 0.199 +- 0.016 (n=7), significantly less than the 0.255+0.013 (n=7) of controls (p
S.104