ELECTRICAL AND CONTRACTILE PROPERTIES OF MUSCLE

在脊椎动物的抽搐肌纤维中，收缩通常由 横向管状系统的膜的去极化。 这 导致钙从肌浆网（SR）内部移动 进入肌浆，在那里它可以与肌钙蛋白上的Ca调节位点结合 从而发生收缩。 研究的长期目标 了解控制SR CA的因素 release. 这些因素之一是管两端的电压 膜，其由电压传感器（二氢吡啶）监测。 受体）帽位于管状膜中。 结构 这种传感器的运动重排引起膜内 电荷移动电流，可以用电压钳检测 法 控制SR Ca释放的另一个因素是游离Ca的值。 [Ca]无论是在大量的肌浆溶液或附近的肌浆 SR释放位点的表面。 钙诱导的钙释放可能起作用 在一些SR钙通道的激活和钙失活中， 钙释放可能发挥作用，关闭SR钙通道，一旦足够的 钙被释放出来，与肌钙蛋白上的大多数钙调节位点结合。 了解这些过程对于了解 骨骼肌被激活。 实验将在青蛙切断的肌纤维上进行 安装在双凡士林间隙室中。 将引发SR Ca释放 通过动作电位或电压钳刺激。 在大多数 在实验中，释放的量和时间过程将用 EGTA-酚红法。 膜内变化电流 将用电压钳方法测量运动。 钙释放 单个SR CA通道将用fluo-3荧光在 激光扫描共聚焦显微镜，作为“钙火花。“一些 实验应该回答的问题是： A.钙释放的钙失活是否显著降低了 在正电压阶跃期间SR Ca释放？ B。钙释放的钙失活是否减少或消除， SR的含量降低了吗？ C.膜内变化运动是如何调节 关闭Ca释放（在不存在Ca失活效应的情况下 释放（？ D.钙释放的钙失活是否有助于关闭 动作电位或电压后复极化过程中的钙释放 SR钙含量正常的纤维中的脉搏？ E.重新激活的SR Ca通道是否能够使Ca失活 释放？ 如果是这样的话，是一个单一的remed通道，屏蔽EGTA从 邻近开放通道的游离[Ca]增加，能够发展 钙释放的钙失活？ F.骨骼肌单个SR钙通道能否记录钙火花 肌肉？ 如果是这样，它们的空间分布是什么，电压是如何 影响它们的频率，它们能持续多久

In vertebrate twitch muscle fibers, contraction is normally activated by a depolarization of the membranes of the transverse tubular system. This leads to a movement of Ca from inside the sarcoplasmic reticulum (SR) into myoplasm where it can bind to the Ca-regulatory sites on troponin so that contraction can occur. The long-term objectives of the research in this application are to understand the factors that control SR CA release. One of these factors is the voltage across the tubular membranes, which is monitored by a voltage sensor (the dihydropyrydine receptor) hat is located in the tubular membranes. Structural rearrangements of movements of this sensor give rise to intramembranous charge movement currents, which can be detected with the voltage-clamp method. Another factor that controls SR Ca release is the value of free [Ca], either in the bulk myoplasmic solution or near the myoplasmic surface of the SR release sites. Ca-induced Ca release may play a role in the activation of some of the SR Ca channels and Ca inactivation of Ca release may play a role in shutting off SR Ca channels once sufficient Ca has been released to bind most of the Ca-regulatory sites on troponin. Understanding these processes is fundamental to understanding how skeletal muscle is activated. The proposed experiments will be carried out on frog cut twitch fibers mounted in a double Vaseline-gap chamber. SR Ca release will be elicited by either action-potential or voltage-clamp stimulation. In most experiments, the amount and time course of release will be measured with the EGTA-phenol red method. Currents from intramembranous change movement will be measured with the voltage-clamp method. Ca release from single SR CA channels will be measured with fluo-3 fluorescence in a laser scan confocal microscope, as "calcium sparks." Some of the questions that the experiments should answer are: A. Does Ca inactivation of Ca release markedly reduce the peak rate of SR Ca release during a positive voltage step? B. Is Ca inactivation of Ca release reduced or eliminated when the Ca content of the SR is reduced? C. How does intramembranous change movement regulate the turning on and turning off of Ca release (in the absence of effects of Ca inactivation of Ca release)? D. Does Ca inactivation of Ca release contribute to the turning off of Ca release during repolarization after an action potential or voltage pulse in a fiber with normal SR Ca content? E. Are reprimed SR Ca channels able to develop Ca inactivation of Ca release? If so, is a single reprimed channel, shielded by EGTA from increases in free [Ca] from neighboring open channels, able to develop Ca inactivation of Ca release? F. Can calcium sparks be recorded from single SR Ca channels in skeletal muscle? If so, what is their spatial distribution, how does voltage affect their frequency, and how long do they last?