Intravesicular calcium transient during calcium release from sarcoplasmic reticulum.
The time course of changes in the intravesicular Ca2+ concentration ([Ca2+]i) in terminal cisternal sarcoplasmic reticulum vesicles upon the induction of Ca2+ release was investigated by using tetramethylmurexide (TMX) as an intravesicular Ca2+ probe. Upon the addition of polylysine at the concentration that led to the maximum rate of Ca2+ release, [Ca2+]i decreased monotonically in parallel with Ca2+ release. Upon induction of Ca2+ release by lower concentrations of polylysine, [Ca2+]i first increased above the resting level, followed by a decrease well below it. The release triggers polylysine, and caffeine brought about dissociation of calcium that bound to a nonvesicular membrane segment consisting of the junctional face membrane and calsequestrin bound to it, as monitored with TMX. No Ca2+ dissociation from calsequestrin-free junctional face membranes or from the dissociated calsequestrin was produced by release triggers, but upon reassociation of the dissociated calsequestrin and the junctional face membrane, Ca2+ dissociation by triggers was restored. On the basis of these results, we propose that the release triggers elicit a signal in the junctional face membrane, presumably in the foot protein moiety, which is then transmitted to calsequestrin, leading to the dissociation of the bound calcium; and in SR vesicles, to the transient increase of [Ca2+]i, and subsequently release across the membrane.
Ikemoto
N
N
Department of Muscle Research, Boston Biomedical Research Institute, Massachusetts 02114.
Antoniu
B
B
Kang
J J
JJ
Mészáros
L G
LG
Ronjat
M
M
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002155:Calsequestrin / Q000378:metabolism; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009114:Murexide / Q000031:analogs & derivatives / Q000378:metabolism; D011107:Polylysine / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D002155:Calsequestrin; D008565:Membrane Proteins; C026042:tetramethylmurexide; D011107:Polylysine; D002110:Caffeine; D009114:Murexide; D002118:Calcium