Blayney L, Thomas H, Muir J, Henderson A
Circ Res. 1978 Oct;43(4):520-6. doi: 10.1161/01.res.43.4.520.
We studied the effects of caffeine on calcium transport by subcellular organelles isolated from rabbit myocardium. Caffeine increased myofibrillar basic and calcium-activated ATPase activity at 20 mM but not at lower concentrations. Mitochondrial and sarcoplasmic reticulum (SR) calcium accumulation was measured both by dual wavelength spectrophotometry with the calcium-sensitive dye, murexide, and by Millipore filtration with 45Ca. In mitochondria, caffeine impaired phosphate-assisted calcium transport but did not alter the closely related parameters of oxygen uptake, P/O ratio (nmol adenosine diphosphate consumed/n ats oxygen consumed, state 3 respiration) or limited calcium loading. In SR, caffeine impaired calcium accumulation. New methods were used to characterize calcium accumulation in the absence of oxalate according to first order reaction kinetics. Caffeine increased the rate constant while decreasing the calcium accumulated. It also increased the associated calcium-activated ATPase activity at low (30 mM) but not high (240 micrometer) external calcium concentration. In the presence of oxalate, caffeine decreased the rate of calcium accumulation, more with low than high calcium concentration. Net efflux of 45Ca from preloaded SR also was increased by caffeine. The findings indicate that caffeine impairs active calcium accumulation by making SR vesicle membranes more permeable to calcium.
我们研究了咖啡因对从兔心肌分离的亚细胞器钙转运的影响。咖啡因在20 mM时可增加肌原纤维碱性和钙激活的ATP酶活性，但在较低浓度时则无此作用。线粒体和肌浆网（SR）的钙积累通过使用钙敏染料紫脲酸铵的双波长分光光度法以及用45Ca进行微孔过滤来测量。在线粒体中，咖啡因损害了磷酸盐辅助的钙转运，但未改变氧摄取、P/O比（消耗的二磷酸腺苷纳摩尔数/消耗的氧纳特数，状态3呼吸）或有限的钙负载等密切相关参数。在SR中，咖啡因损害了钙积累。我们使用新方法根据一级反应动力学来表征在无草酸盐情况下的钙积累。咖啡因增加了速率常数，同时减少了积累的钙。在低（30 mM）而非高（240微米）外部钙浓度下，它还增加了相关的钙激活ATP酶活性。在有草酸盐存在的情况下，咖啡因降低了钙积累速率，低钙浓度时比高钙浓度时降低得更多。咖啡因还增加了预加载SR中45Ca的净流出量。这些发现表明，咖啡因通过使SR囊泡膜对钙更具通透性而损害了主动钙积累。
