Activation of Ca2+ release in isolated sarcoplasmic reticulum

Abstract

The relationship between Ca2+ release from sarcoplasmic reticulum, induced by elevated pH, tetraphenylboron (TPB-) or chemical modification, and the change in the surface charge of the membranes as measured by the fluorescence intensity of anilinonaphthalene sulfonate (ANS) is examined. The simulated Ca2+ release is inhibited by dicyclohexylcarbodiimide and external Ca2+. TPB-, but not tetraphenylarsonium (TPA+), causes a decrease in ANS- fluorescence, with 50% decrease occurring at about 5 microM TPB-. The decrease in ANS- fluorescence as well as the inhibition of Ca2+ accumulation induced by TPB- are prevented by TPA+. A linear relationship between the decrease in membrane surface potential and the extent of the Ca2+ released by TPB- is obtained. Similar levels of [3H]TPB-bound to sarcoplasmic reticulum membranes were obtained regardless of whether or not the vesicles have taken up Ca2+. The inhibition of Ca2+ accumulation and the [3H]TPB- incorporation into the membranes were correlated. Ca2+ release from sarcoplasmic reticulum, by pH elevation, chemical modification or by addition of NaSCN (0.2 to 0.5 M) or the Ca2+ ionophore ionomycin, is also accompanied by a decrease in ANS- fluorescence intensity. However, chemical modification and elevated pH affects the surface potential much less than SCN- or TPB- do. These results suggest that the enhancement of Ca2+ release by these treatments is not due to a general effect on the membrane surface potential, but rather through the modification of a specific protein. They also suggest that membrane surface charges might play an important role in the control mechanism of Ca2+ release.

Trypsinized Cerebellar Inositol 1,4,5-Trisphosphate Receptor

“…IP 3 (1 M) and Ca 2ϩ ionophore A23187 (4 M) were added when the [Ca 2ϩ ] was ϳ220 nM. Trypsin (ϩϩ) microsomes showed no significant reduction in A23187-releasable Ca 2ϩ store size (estimated from A23187-induced Ca 2ϩ release; AICR) as well as AICU activity, a finding consistent with data that the SERCA/ Ca 2ϩ pump in the SR is relatively resistant to limited trypsinolysis (34). However, as the digestion time was extended, the active AICU activity tended to be attenuated, since it took longer to settle the [Ca 2ϩ ] level to ϳ220 nM in trypsin(ϩϩ) microsomes than in trypsin(Ϫ) microsomes (Fig.…”

High‐affinity Ca2+‐binding site inhibiting Ca2+ release from sarcoplasmic reticulum

“…We have studied Ca 2÷ release in unfractionated native SR membranes and have developed several different conditions for activation of Ca 2÷ release [4][5][6][7]19]. This Ca2+-release system is present in all structural regions of the SR membranes, and apparently operates via a channel different from the junctional Ca2+-release channel.…”

“…Recent studies indicate that there is more than one Ca2+-release system in the sarcoplasmic reticulum, involving two or more types of divalent cation channels [6,7,[9][10][11][12][13][14][15][16]. These channels differ …”

“…Ca 2÷ release from the sarcoplasmic reticulum (SR) plays an important role in excitationcontraction coupling [1]. Using skinned muscle fibers and isolated SR membranes, various treatments and stimuli, such as addition of Ca 2+ [2], depolarization of the membrane [3], alteration in pH [4] or surface charge [5], chemical modifications of the membranes [6,7], or the presence of inositol trisphosphate [8], have been shown to induce Ca 2+ release.…”

“…Recent studies indicate that there is more than one Ca2+-release system in the sarcoplasmic reticulum, involving two or more types of divalent cation channels [6,7,[9][10][11][12][13][14][15][16]]. These channels differ trans-l,2-diamino-cyclohexane-N,N,N',N'-tetraacetic acid; RR, ruthenium red; TPB-, tetraphenylboron; SR, sarcoplasmic reticulum in: their divalent cation conductivity and specificity, their distribution in the different structural regions of the SR membrane, and also in their activation mechanism.…”