Morrissette J, Xu L, Nelson A, Meissner G, Block B A
Hopkins Marine Station, Stanford University, Pacific Grove, California 93950, USA.
Am J Physiol Regul Integr Comp Physiol. 2000 Nov;279(5):R1889-98. doi: 10.1152/ajpregu.2000.279.5.R1889.
Two distinct skeletal muscle ryanodine receptors (RyR1s) are expressed in a fiber type-specific manner in fish skeletal muscle (11). In this study, we compare [(3)H]ryanodine binding and single channel activity of RyR1-slow from fish slow-twitch skeletal muscle with RyR1-fast and RyR3 isolated from fast-twitch skeletal muscle. Scatchard plots indicate that RyR1-slow has a lower affinity for [(3)H]ryanodine when compared with RyR1-fast. In single channel recordings, RyR1-slow and RyR1-fast had similar slope conductances. However, the maximum open probability (P(o)) of RyR1-slow was threefold less than the maximum P(o) of RyR1-fast. Single channel studies also revealed the presence of two populations of RyRs in tuna fast-twitch muscle (RyR1-fast and RyR3). RyR3 had the highest P(o) of all the RyR channels and displayed less inhibition at millimolar Ca(2+). The addition of 5 mM Mg-ATP or 2.5 mM beta, gamma-methyleneadenosine 5'-triphosphate (AMP-PCP) to the channels increased the P(o) and [(3)H]ryanodine binding of both RyR1s but also caused a shift in the Ca(2+) dependency curve of RyR1-slow such that Ca(2+)-dependent inactivation was attenuated. [(3)H]ryanodine binding data also showed that Mg(2+)-dependent inhibition of RyR1-slow was reduced in the presence of AMP-PCP. These results indicate differences in the physiological properties of RyRs in fish slow- and fast-twitch skeletal muscle, which may contribute to differences in the way intracellular Ca(2+) is regulated in these muscle types.
两种不同的骨骼肌兰尼碱受体（RyR1s）以纤维类型特异性方式在鱼类骨骼肌中表达（11）。在本研究中，我们比较了鱼类慢肌骨骼肌中RyR1-slow与快肌骨骼肌中分离出的RyR1-fast和RyR3的[³H]兰尼碱结合及单通道活性。Scatchard图表明，与RyR1-fast相比，RyR1-slow对[³H]兰尼碱的亲和力较低。在单通道记录中，RyR1-slow和RyR1-fast具有相似的斜率电导。然而，RyR1-slow的最大开放概率（P(o)）比RyR1-fast的最大P(o)低三倍。单通道研究还揭示了金枪鱼快肌中存在两种RyR群体（RyR1-fast和RyR3）。RyR3在所有RyR通道中具有最高的P(o)，并且在毫摩尔级Ca²⁺浓度下表现出较少的抑制作用。向通道中添加5 mM Mg-ATP或2.5 mM β,γ-亚甲基腺苷5'-三磷酸（AMP-PCP）可增加两种RyR1的P(o)和[³H]兰尼碱结合，但也导致RyR1-slow的Ca²⁺依赖性曲线发生偏移，使得Ca²⁺依赖性失活减弱。[³H]兰尼碱结合数据还表明，在AMP-PCP存在下，Mg²⁺对RyR1-slow的抑制作用降低。这些结果表明鱼类慢肌和快肌骨骼肌中RyR的生理特性存在差异,这可能导致这些肌肉类型中细胞内Ca²⁺调节方式的差异。
