Effect of Mg2+ and ATP on depolarization-induced Ca2+ release in isolated triads.
The effect of different free Mg2+ and ATP concentrations on depolarization-induced Ca2+ release in isolated skeletal muscle triadic vesicles was examined by simultaneously monitoring direct effects on ryanodine receptors from either isolated or coupled terminal cisternae. Free Mg2+ was increased to concentrations of 11-14 microM, 81 microM, 175-181 microM, and 1 mM while total ATP concentration was kept constant or MgATP concentration was kept constant. We observed the following. 1) Increasing MgATP reduces the measurable Ca2+ release from isolated vesicles by stimulating the Ca(2+)-ATPase in the terminal cisternae. 2) Half-maximal inhibition of functionally coupled ryanodine receptors during depolarization-induced Ca2+ release is observed at 1 mM Mg2+, whereas half-maximal inhibition of the nondepolarized ryanodine receptor is seen at 75 microM Mg2+ at the same free ATP and MgATP concentrations. 3) Two separate time constants for Ca2+ release were obtained for nondepolarized ryanodine receptors with free Mg2+ at 14 microM and free ATP at 6.1 mM; this may represent triadic ryanodine receptors vs. isolated terminal cisternae ryanodine receptors.
Ritucci
N A
NA
Department of Physiology and Biophysics, Wright State University, Dayton, Ohio 45435, USA.
Corbett
A M
AM
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D004594:Electrophysiology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D009124:Muscle Proteins / Q000378:metabolism / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D011817:Rabbits; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium