Effects of external calcium reduction on the kinetics of potassium contractures in frog twitch muscle fibres

The Journal of Physiology
G Cota, E Stefani

Abstract

1. The amplitude and time course of K contractures (Cl- constant) of single twitch muscle fibres of the frog have been analysed in three external Ca2+ concentrations. 2. The resting potential, effective resistance, threshold for the Na current and K-induced depolarizations were not modified by replacing 1.8 mM-Ca2+ by 3 mM-Mg2+ in absence (low-Ca saline: 3-6 micro M-Ca2+) or in the presence of 5 mM-EGTA (Ca-free saline: less than or equal to 10(-9) M-Ca2+). 3. The tension development during the initial phase of K contractures was independent of external Ca2+ while the amplitude, the duration and the time constant of spontaneous relaxation decreased progressively as Ca2+ concentration was diminished. 4. When the concentration of Mg2+ was increased to 5 mM in Ca-free saline K contractures were slower and smaller than those in 3 mM-Mg2+. 5. In Ca-free saline the activation curve (peak tension vs. logarithm of external K+ concentration) shifted by 3-5 mV towards more positive potentials while the inactivation curve (peak tension of the test contracture vs. logarithm of external K+ concentration during the conditioning period) shifted by 16-18 mV towards more negative potentials. Both curves became steeper in Ca-free saline. 6. The ...Continue Reading

Citations

Apr 1, 1990·Pflügers Archiv : European journal of physiology·C CognardG Raymond
Jan 1, 1992·Progress in Biophysics and Molecular Biology·A F Dulhunty
Jan 1, 1985·Progress in Biophysics and Molecular Biology·J CailléO Rougier
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Sep 1, 1995·Pflügers Archiv : European journal of physiology·M PattersonG Raymond
Jul 1, 1989·Pflügers Archiv : European journal of physiology·D Feldmeyer
May 23, 2014·The Journal of Biological Chemistry·Francisco AltamiranoJosé R López
Jun 1, 1992·Journal of Muscle Research and Cell Motility·M C GarciaJ A Sanchez
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