St Louis P J, Sulakhe P V
Can J Biochem. 1976 Nov;54(11):946-56. doi: 10.1139/o76-137.
Sarcolemma isolated from guinea pig heart ventricles possessed ATP-dependent Ca2+ binding and accumulation (+ oxalate) activities which were not inhibited by sodium azide, oligomycin, or ruthenium red. Ca2+ binding and accumulation by sarcolemma were sensitive to pH, the optimum being about pH 6.8. The concentrations of ATP required for half-maximal binding and accumulation were 94.3 and 172 muM, respectively. Mg2+ up to 5 mM significantly enhanced both activities but was inhibitory at higher concentrations (greater than 10 mM). Sarcolemmal Ca2+ binding and accumulation were stimulated 100% by K+, half-maximal enhancement occurring at 5-10 mM K+. Ca2+ binding and accumulation were both saturable processes and the respective apparent Km values for Ca2+ were 16.4 and 14.3 muM. Ca2+ binding by sarcolemma was a rapid process and the bound Ca2+ was released upon depletion of ATP in the medium. It is suggested that the sarcolemmal Ca2+ transport system may well be of significance in regulation of the contraction-relaxation cycle of cardiac muscle.
从豚鼠心脏心室分离得到的肌膜具有依赖ATP的Ca2+结合和积累（+草酸盐）活性，这些活性不受叠氮化钠、寡霉素或钌红的抑制。肌膜的Ca2+结合和积累对pH敏感，最适pH约为6.8。半最大结合和积累所需的ATP浓度分别为94.3和172μM。高达5 mM的Mg2+显著增强了这两种活性，但在更高浓度（大于10 mM）时具有抑制作用。肌膜Ca2+结合和积累受到K+的100%刺激，在5-10 mM K+时出现半最大增强。Ca2+结合和积累都是可饱和过程，Ca2+的各自表观Km值分别为16.4和14.3μM。肌膜的Ca2+结合是一个快速过程，并且当培养基中的ATP耗尽时，结合的Ca2+会释放出来。有人认为，肌膜Ca2+转运系统在调节心肌收缩-舒张周期中可能具有重要意义。
