Donoso P, Prieto H, Hidalgo C
Departamento de Fisiología y Biofísica, Facultad de Medicina, Universidad de Chile, Santiago.
Biophys J. 1995 Feb;68(2):507-15. doi: 10.1016/S0006-3495(95)80212-2.
Triads isolated from frog and rabbit skeletal muscle were equilibrated with different external [Ca2+], ranging from 0.025 to 10 mM. Vesicular calcium increased with external [Ca2+] as the sum of a linear plus a saturable component; the latter, which vanished after calsequestrin removal, displayed Bmax values of 182 and 132 nmol of calcium/mg of protein, with Kd values of 1.21 and 1.14 mM in frog and rabbit vesicles, respectively. The effect of luminal [Ca2+] on release kinetics in triads from frog and rabbit skeletal muscle was investigated, triggering release with 2 mM ATP, pCa 5, pH 6.8. In triads from frog, release rate constant (k) values increased sixfold after increasing luminal [Ca2+] from 0.025 to 3 mM. In triads from rabbit, k values increased 20-fold when luminal [Ca2+] increased from 0.05 to 0.7 mM. In both preparations, k values remained relatively constant (10-12 s-1) at higher luminal [Ca2+], with a small decrease at 10 mM. Initial release rates increased with luminal [Ca2+] in both preparations; in triads from rabbit the increase was hyperbolic, and in triads from frogs the increase was sigmoidal. These results indicate that, although triads from frog and rabbit respond differently, in both preparations luminal [Ca2+] has a distinctive effect on release, presumably by regulating sarcoplasmic reticulum calcium channels.
从青蛙和兔子骨骼肌分离出的三联体与不同的细胞外[Ca2+]（范围从0.025到10 mM）进行平衡。囊泡钙随着细胞外[Ca2+]的增加而增加，呈现为线性成分与饱和成分之和；后者在肌钙蛋白去除后消失，在青蛙和兔子的囊泡中，其Bmax值分别为182和132 nmol钙/毫克蛋白质，Kd值分别为1.21和1.14 mM。研究了管腔[Ca2+]对青蛙和兔子骨骼肌三联体释放动力学的影响，在2 mM ATP、pCa 5、pH 6.8的条件下触发释放。在青蛙的三联体中，当管腔[Ca2+]从0.025 mM增加到3 mM时，释放速率常数（k）值增加了六倍。在兔子的三联体中，当管腔[Ca2+]从0.05 mM增加到0.7 mM时，k值增加了20倍。在两种标本中，在较高的管腔[Ca2+]下，k值保持相对恒定（10 - 12 s-1），在10 mM时略有下降。两种标本的初始释放速率均随管腔[Ca2+]增加；在兔子的三联体中增加呈双曲线，在青蛙的三联体中增加呈S形。这些结果表明，尽管青蛙和兔子的三联体反应不同，但在两种标本中管腔[Ca2+]对释放都有独特的影响，可能是通过调节肌浆网钙通道来实现的。
