Effects of alkaline pH on sarcoplasmic reticulum Ca2+ release and Ca2+ uptake.
Alkalinization-induced Ca2+ release from isolated frog or rabbit sarcoplasmic reticulum vesicles appears to consist of two distinct components: 1) a direct activation of ruthenium red-sensitive Ca2+ release channels in terminal cisternae and 2) an increased ruthenium red-insensitive Ca2+ efflux through some other efflux pathway distributed throughout the sarcoplasmic reticulum. The first of these releases exhibits an alkalinization-induced inactivation process and does not depend on the ruthenium red-insensitive form of Ca2+ release as a triggering agent for secondary Ca(2+)-induced Ca2+ release. Both releases are inhibited when the extravesicular (i.e. cytoplasmic) free [Ca2+] is reduced. This may reflect an increased sensitivity of the Ca2+ release channels to Ca2+ at alkaline pH. The pH sensitivity of the ruthenium red-sensitive Ca2+ release channels could be of significance during excitation-contraction coupling. The ruthenium red-insensitive form of Ca2+ release is less likely to be physiologically relevant, but it probably has contributed greatly to reports of alkalinization-induced decreases in net sarcoplasmic reticulum Ca2+ uptake, particularly under conditions where oxalate supported Ca2+ uptake is much less affected, as here.
Dettbarn
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C
Department of Physiology and Biophysics, University of Texas Medical Branch, Galveston 77550.
Palade
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P
D000585:Aminacrine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002451:Cell Compartmentation; D002474:Cell-Free System; D004229:Dithiothreitol / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism*; D010539:Permeability; D011817:Rabbits; D011898:Ranidae; D012430:Ruthenium Red / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013748:Tetracaine / Q000494:pharmacology
D015220:Calcium Channels; D013748:Tetracaine; D012430:Ruthenium Red; D001464:Barium; D000585:Aminacrine; D000252:Calcium-Transporting ATPases; D005978:Glutathione; D002118:Calcium; D004229:Dithiothreitol