Pang D C
Adv Myocardiol. 1980;1:43-53.
Calcium binding to fragmented sarcolemma isolated from dog heart was measured by an ultracentrifugation technique. Two classes of binding sites with dissociation constants of 4.2 x 10(-5) M and 1.2 x 10(-3) M were identified. The maximum number of high and low affinity sites were 15 and 452 nmol/mg, respectively. The effects of various cations and drugs on calcium binding were studied in the presence of 0.1 mM total calcium. All cations tested inhibited calcium binding to a certain degree. La3+ (1 mM) and Mn2+ (1 mM) abolished calcium binding to the sarcolemma. The other divalent cation, Mg2+, used at a concentration of 1 mM, produced a partial inhibition Na+ and K+ also depressed calcium binding, with Na+ being the more potent inhibitor. Verapamil produced a depression at concentrations as low as 10(-7) M and abolished calcium binding at 10(-3) M. The effects of these cations and drugs on fragmented sarcolemma appear different from those reported for the isolated sarcoplasmic reticulum. Thus it is unlikely that the calcium binding observed was caused by a contamination of the sarcolemmal preparation by the fragmented sarcoplasmic reticulum. In addition, the calcium binding seems to be on the sarcolemma itself, rather than to the remaining fragments of the basement membrane, because the calcium binding was not significantly modified by pretreatment with purified neuraminidase (0.25 U/g of sarcolemma).
采用超速离心技术测定了从犬心脏分离出的破碎肌膜的钙结合情况。鉴定出两类解离常数分别为4.2×10⁻⁵ M和1.2×10⁻³ M的结合位点。高亲和力和低亲和力位点的最大数量分别为15和452 nmol/mg。在总钙浓度为0.1 mM的情况下，研究了各种阳离子和药物对钙结合的影响。所有测试的阳离子均在一定程度上抑制钙结合。La³⁺（1 mM）和Mn²⁺（1 mM）使钙与肌膜的结合消失。另一种二价阳离子Mg²⁺，浓度为1 mM时，产生部分抑制作用。Na⁺和K⁺也降低钙结合，其中Na⁺是更有效的抑制剂。维拉帕米在低至10⁻⁷ M的浓度下就产生抑制作用，在10⁻³ M时使钙结合消失。这些阳离子和药物对破碎肌膜的作用似乎与报道的分离肌浆网的作用不同。因此，观察到的钙结合不太可能是由于破碎肌浆网污染肌膜制剂所致。此外，钙结合似乎是在肌膜本身，而不是在基底膜的剩余片段上，因为用纯化的神经氨酸酶（0.25 U/g肌膜）预处理并没有显著改变钙结合。
