Jong D S, Pape P C, Chandler W K, Baylor S M
Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut 06510-8026.
J Gen Physiol. 1993 Aug;102(2):333-70. doi: 10.1085/jgp.102.2.333.
Cut fibers from Rana temporaria and Rana pipiens (striation spacing, 3.9-4.2 microns) were mounted in a double Vaseline-gap chamber and studied at 14 degrees C. The Ca indicator purpurate-3,3' diacetic acid (PDAA) was introduced into the end pools and allowed to diffuse into the optical recording site. When the concentration at the site exceeded 2 mM, step depolarizations to 10 mV were applied and the [Ca] transient measured with PDAA was used to estimate Ca release from the sarcoplasmic reticulum (SR) (Baylor, S. M., W. K. Chandler, and M. W. Marshall. 1983. Journal of Physiology. 344:625-666). With depolarization, the rate of SR Ca release increased to an early peak and then rapidly decreased several-fold to a quasi-steady level. The total amount of Ca released from the SR at the time of peak rate of release appeared to be independent of SR Ca content, consistent with the idea that a single activated channel might pass, on average, a fixed number of ions, independent of the magnitude of the single channel flux. A possible explanation of this property is given in terms of locally induced Ca inactivation of Ca release. The solution in the end pools was then changed to one with PDAA plus fura-2. SR Ca release was estimated from the [Ca] transient, as before, and from the delta [Cafura-2] signal. On average, 2-3 mM fura-2 increased the quasi-steady level of the rate of SR Ca release by factors of 6.6 and 3.8, respectively, in three fibers from Rana temporaria and three fibers from Rana pipiens. The peak rate of release was increased in five of the six fibers but to a lesser extent than the quasi-steady level. In all fibers, the amplitude of the free [Ca] transient was markedly reduced. These increases in the rate of SR Ca release are consistent with the idea that Ca inactivation of Ca release develops during a step depolarization to 10 mV and that 2-3 mM fura-2 is able to reduce this inactivation by complexing Ca and thereby reducing free [Ca]. Once the concentration of fura-2 becomes sufficiently large, a further increase reduces the rate of SR Ca release. On average, 5-6 mM fura-2 increased the quasi-steady rate of release, compared with 0 mM fura-2, by 6.5 and 2.9, respectively, in four fibers from Rana temporaria and three from Rana pipiens.(ABSTRACT TRUNCATED AT 400 WORDS)
从林蛙（Rana temporaria）和豹蛙（Rana pipiens）（肌节间距为3.9 - 4.2微米）获取的肌纤维被安装在双凡士林间隙池中，并在14摄氏度下进行研究。将钙指示剂紫尿酸-3,3'-二乙酸（PDAA）引入端池，并使其扩散到光学记录部位。当该部位的浓度超过2 mM时，施加10 mV的阶跃去极化，并用PDAA测量的[Ca]瞬变来估计肌浆网（SR）的钙释放（贝勒，S.M.，W.K.钱德勒和M.W.马歇尔。1983年。《生理学杂志》。344:625 - 666）。随着去极化，SR钙释放速率增加到一个早期峰值，然后迅速下降几倍至一个准稳态水平。在释放速率峰值时从SR释放的钙总量似乎与SR钙含量无关，这与单个激活通道平均可能通过固定数量离子的观点一致，而与单通道通量大小无关。根据局部诱导的钙释放失活对此特性给出了一种可能的解释。然后将端池中的溶液换成含有PDAA加fura - 2的溶液。如前所述，从[Ca]瞬变以及从δ[Cafura - 2]信号估计SR钙释放。平均而言，在来自林蛙的三根肌纤维和来自豹蛙的三根肌纤维中，2 - 3 mM的fura - 2分别使SR钙释放速率的准稳态水平提高了6.6倍和3.8倍。在六根纤维中的五根中，释放峰值速率有所增加，但增加幅度小于准稳态水平。在所有纤维中，游离[Ca]瞬变的幅度明显降低。SR钙释放速率的这些增加与以下观点一致：在阶跃去极化至10 mV期间会发生钙释放的钙失活，并且2 - 3 mM的fura - 2能够通过络合钙从而降低游离[Ca]来减少这种失活。一旦fura - 2的浓度变得足够高，进一步增加反而会降低SR钙释放速率。平均而言，与0 mM fura - 2相比，在来自林蛙的四根肌纤维和来自豹蛙的三根肌纤维中，5 - 6 mM的fura - 2分别使释放的准稳态速率提高了6.5倍和2.9倍。（摘要截选至400字）
