Non-mitochondrial calcium ion regulation in rat ventricular myocytes

Abstract

Ca 2+ exchange has been measured in a suspension of rat ventricular myocytes treated with digitonin or saponin to render the sarcolemma permeable to small molecules and ions. Two fractions of exchange were identified, one that was attributed to the mitochondrial component of the cell and the other to a non-mitochondrial fraction. Mitochondrial Ca 2+ uptake was blocked by sodium azide and depended on respiratory substrates whereas non-mitochondrial uptake occurred independently of these molecules but was dependent on ATP and creatine phosphate. Non-mitochondrial Ca 2+ uptake could be induced at a Ca 2+ concentration below 1 um and the initial rate increased with concentration up to 100 um Uptake could be reversed by sulmazole (a caffeine-like substance) and this reversal in turn inhibited by ryanodine. These properties suggest that the major locus for non-mitochondrial Ca 2+ exchange is at the sarcoplasmic reticulum. Ca 2+ exchange could be modulated by a number of agents, including carnosine, but was unaffected by others, including Na + , inositol trisphosphate and cyclic AMP. A kinetic model of the data is presented, which incorporates similar data of Ca 2+ uptake into the mitochondrial fraction. The rates of Ca 2+ exchange measured in these experiments suggest that these two components of the cell can reduce the sarcoplasmic Ca 2+ concentration rapidly enough to account for the observed transient nature of the isometric twitch. Furthermore, it is suggested that both non-mitochondrial and mitochondrial fractions of the cell could significantly contribute to tension relaxation in rat cardiac muscle.

Growing Old Too Early: Skeletal Muscle Single Fiber Biomechanics in Ageing R349P Desmin Knock-in Mice Using the MyoRobot Technology

“…RS served as release solution for Ca 2+ ions from the SR and was LR supplemented with 30 mM caffeine. All solutions were thawed from stocks at the day of experiments and freshly supplemented with creatine kinase (CK, Sigma-Aldrich/Merck KGaA, Darmstadt, Germany) to ∼300 U/ml or ∼3 U/well and sodium azide (0.1 M NaN 3 ), the latter to prevent mitochondrial Ca 2+ uptake ( [46]). To initially chemically permeabilize a single fiber, saponin was added to HR in a separate well of the MyoRobot rack to a concentration of 0.1% (w/v).…”

Total and free myoplasmic calcium during a contraction cycle: x‐ray microanalysis in guinea‐pig ventricular myocytes.

“…The systolic increase in ECamito was a short-lasting phenomenon which would not have been recorded when the preparations were shock-frozen at the peak of contraction (Table 2), and EPMA of XCamyo timed at 30-45 ms after start of excitation has not been reported up to now. However, significant uptake and egress of mitochondrial calcium during the cardiac cycle has been calculated by extrapolation of measurements of calcium shifts in suspensions of isolated ventricular myocytes (Fry, Powell, Twist & Ward, 1984;Fry, Harding & Miller, 1989). One is tempted to speculate that the transient changes of XCamito are involved in the calcium regulation of mitochondrial enzymes during the contraction cycle (Krause et al 1987;McCormack, Halestrap & Denton, 1990).…”

Growing old too early, automated assessment of skeletal muscle single fiber biomechanics in ageing R349P desmin knock-in mice using the MyoRobot technology

“…RS served as release solution for Ca 2+ ions from the SR and was LR supplemented with 30 mM caffeine. All solutions were thawed from stocks at the day of experiments and freshly supplemented with creatine kinase (CK, Sigma/Roche, Germany) to ~300 U/ml or ~3 U/well and sodium azide (0.1 M NaN 3 ), the latter to prevent mitochondrial Ca 2+ uptake Fry et al (1989) . To initially chemically permeabilize a single fiber, saponin was added to HR in a separate well of the MyoRobot rack to a concentration of 0.1% (w/v).…”