Characterization of "depolarization"-induced calcium release from sarcoplasmic reticulum in vitro with the use of membrane potential probe.
In the triad, the complex of transverse (T) tubule and sarcoplasmic reticulum (SR) Ca2+ release is induced from SR by mediation of the T-tubule. We report here evidence that this Ca2+ release is produced by depolarization of the T-tubule moiety. Thus, we found that the amount of [14C]SCN- taken up by T-tubules and triads (but not that by SR) increased upon incubation with (K, Na) gluconate, Mg ATP, indicating that the T-tubule was polarized making the lumenal side (equivalent to the extracellular side of an intact muscle fiber) more positive. Upon mixing with choline chloride, the procedure to induce Ca2+ release, [14C]SCN- uptake decreased, indicating that the T-tubule became depolarized. Activation of the T-tubule polarization by Na+ and prevention of it by digoxin [inhibitor of the (Na+, K+) pump], respectively, led to activation and inhibition of choline chloride-induced SR Ca2+ release.
Ikemoto
N
N
Department of Muscle Research, Boston Biomedical Research Institute, MA 02114.
Antoniu
B
B
Kang
J J
JJ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002794:Choline / Q000494:pharmacology; D004077:Digoxin / Q000494:pharmacology; D007700:Kinetics; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D013861:Thiocyanates / Q000378:metabolism
D002250:Carbon Radioisotopes; D013861:Thiocyanates; D004077:Digoxin; D012964:Sodium; D002794:Choline; D002118:Calcium