### Abstract

Ca^{2+} activated isometric tension in mechanically skinned rat ventricular fibers were measured in solutions containing 3X10^{-5} M, 1X10^{-4} M, 1X10^{-3} M, and 2X10^{-3} M free MgATP^{2-}. In addition all solutions contained 7 mM EGTA, 70 mM K^{+}, Cl^{-}, 50 μM Mg^{2+}, 15 mM creatine phosphate, creatine phosphokinase, imidazole and varying amounts of Ca^{2+} (pH = 7.0, ionic strength = 0.15 M, T = 21°C). For each [MgATP^{2-}] the mean percent of maximum tension was plotted vs pCa and sigmoid curves were fit using the Hill equation. Increasing [MgATP^{2-}] shifted the pCa vs percent maximum tension relationship in the direction of increasing Ca^{2+} required for activation. The pCa which produced 50% of maximum tension was 5.8, 5.3, 5.4, 5.5 for 3X10^{-5} M, 1X10^{-4} M, 1X10^{-3} M, and 2X10^{-3} M MgATP^{2-} solutions. The Hill coefficients (1.19, 1.24, 2.20, 2.99) and the steepness of the curves increased as the [MgATP^{2-}] was elevated. This change in steepness accounts for the slightly lower [Ca^{2+}] needed for half maximum tension as the [MgATP^{2-}] is increased to millimolar levels. The shift in the pCa vs percent tension relationship as [MgATP^{2-}] is changed from 3X10^{-5} M to 1X10^{-4} M is consistent with the hypothesis of Weber and co workers that a critical number of rigor bridges can affect the requlatory properties of troponin. The increases in slope at higher MgATP^{2-} levels suggest that even in the absence of rigor bridges the Ca^{2+} sensitivity may be affected by the formation of a critical number of force generating bridges.

Original language | English |
---|---|

Journal | Biophysical Journal |

Volume | 15 |

Issue number | 2 II |

State | Published - Dec 1 1975 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Biophysics

### Cite this

**Effects of magnesium adenosine triphosphate on submaximal calcium activated tension in skinned cardiac cells.** / Best, P. M.; Kerrick, W. Glenn.

Research output: Contribution to journal › Article

*Biophysical Journal*, vol. 15, no. 2 II.

}

TY - JOUR

T1 - Effects of magnesium adenosine triphosphate on submaximal calcium activated tension in skinned cardiac cells

AU - Best, P. M.

AU - Kerrick, W. Glenn

PY - 1975/12/1

Y1 - 1975/12/1

N2 - Ca2+ activated isometric tension in mechanically skinned rat ventricular fibers were measured in solutions containing 3X10-5 M, 1X10-4 M, 1X10-3 M, and 2X10-3 M free MgATP2-. In addition all solutions contained 7 mM EGTA, 70 mM K+, Cl-, 50 μM Mg2+, 15 mM creatine phosphate, creatine phosphokinase, imidazole and varying amounts of Ca2+ (pH = 7.0, ionic strength = 0.15 M, T = 21°C). For each [MgATP2-] the mean percent of maximum tension was plotted vs pCa and sigmoid curves were fit using the Hill equation. Increasing [MgATP2-] shifted the pCa vs percent maximum tension relationship in the direction of increasing Ca2+ required for activation. The pCa which produced 50% of maximum tension was 5.8, 5.3, 5.4, 5.5 for 3X10-5 M, 1X10-4 M, 1X10-3 M, and 2X10-3 M MgATP2- solutions. The Hill coefficients (1.19, 1.24, 2.20, 2.99) and the steepness of the curves increased as the [MgATP2-] was elevated. This change in steepness accounts for the slightly lower [Ca2+] needed for half maximum tension as the [MgATP2-] is increased to millimolar levels. The shift in the pCa vs percent tension relationship as [MgATP2-] is changed from 3X10-5 M to 1X10-4 M is consistent with the hypothesis of Weber and co workers that a critical number of rigor bridges can affect the requlatory properties of troponin. The increases in slope at higher MgATP2- levels suggest that even in the absence of rigor bridges the Ca2+ sensitivity may be affected by the formation of a critical number of force generating bridges.

AB - Ca2+ activated isometric tension in mechanically skinned rat ventricular fibers were measured in solutions containing 3X10-5 M, 1X10-4 M, 1X10-3 M, and 2X10-3 M free MgATP2-. In addition all solutions contained 7 mM EGTA, 70 mM K+, Cl-, 50 μM Mg2+, 15 mM creatine phosphate, creatine phosphokinase, imidazole and varying amounts of Ca2+ (pH = 7.0, ionic strength = 0.15 M, T = 21°C). For each [MgATP2-] the mean percent of maximum tension was plotted vs pCa and sigmoid curves were fit using the Hill equation. Increasing [MgATP2-] shifted the pCa vs percent maximum tension relationship in the direction of increasing Ca2+ required for activation. The pCa which produced 50% of maximum tension was 5.8, 5.3, 5.4, 5.5 for 3X10-5 M, 1X10-4 M, 1X10-3 M, and 2X10-3 M MgATP2- solutions. The Hill coefficients (1.19, 1.24, 2.20, 2.99) and the steepness of the curves increased as the [MgATP2-] was elevated. This change in steepness accounts for the slightly lower [Ca2+] needed for half maximum tension as the [MgATP2-] is increased to millimolar levels. The shift in the pCa vs percent tension relationship as [MgATP2-] is changed from 3X10-5 M to 1X10-4 M is consistent with the hypothesis of Weber and co workers that a critical number of rigor bridges can affect the requlatory properties of troponin. The increases in slope at higher MgATP2- levels suggest that even in the absence of rigor bridges the Ca2+ sensitivity may be affected by the formation of a critical number of force generating bridges.

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M3 - Article

VL - 15

JO - Biophysical Journal

JF - Biophysical Journal

SN - 0006-3495

IS - 2 II

ER -