Electrophysiological study on the physiological roles of the oscillatory release of calcium from the sarcoplasmic reticulum in myocardium.

心肌肌浆网振荡释放钙的生理作用的电生理学研究。

基本信息

批准号：
61570048
负责人：
EHARA Tsuguhisa
金额：
$ 1.47万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

The electrical and mechanical activities related to the oscillatory release of Ca from the sarcoplasmic reticulum (SR) were studied in muscle preparations and single myocytes isolated from guinea-pig ventricles. In partially depolarized papillary muscles, rapid stimulation (1 Hz) in the presence of <beta>-adrenergic stimulants induced oscillatory afterpotentials (OAP) and aftercontractions (AC) which were produced by the oscillatory release of Ca from SR. Mg ions at concentrations of 5-12 mM were found to suppress these OAP and AC. However, Mg potentiated the twitch contractions, and this effect was due to suppression of the oscillatory release of Ca from SR during diastole. Thus, the Ca oscillation at SR appeared to decrease the amount of Ca in SR avaliable for twitch. Since microscopic Ca oscillations may be present even in normal myocardium, the above results suggest that such oscillaltions can be an important mechanism regulating the amount of Ca in SR as well as the cellular Ca ho … More meostasis, provided there is a link between these oscillations and the Ca-extruding function of the sarcolemma. In voltage-clamped isolated myocytes, high concentrations (15-25 mM) of caffeine, which releases Ca from SR, were found to induce pulse-like small (20-30 pA at the resting potential) inward currents. These currents appeard to be activated by the intracellular Ca, since Ca injection into the cell or application of large depolarizations which produced a tonic tension enhanced them. The currents were Na-dependent but could flow in the presence of Li instead of Na. The pulse-like development suggested that the currents were generated in the membrane sites which distributed relatively scarcely in the sarcolemma. The most probable sites are those facing the juxtamembranous SR. observed currents might reflect one aspect of the functional coupling of the sarcolemma and SR. We are now further studying the nature of these currents. Another type of the Ca-activated electrical event was also noted in isolated myocytes with the patch clamp technique. This was the current through the Ca-activated non-specific cation channel, and its properties were quantiatively analyzed. This current contributes to the Ca-mediated steady background conductance and does not generate pulse-like electrical events in the whole cell level. Less

在肌肉制剂和从豚鼠心室分离的单个肌细胞中，在存在快速刺激（1 Hz）的情况下，研究了与肌浆网（SR）中Ca振荡释放相关的电和机械活动。 β-肾上腺素能兴奋剂诱导振荡后电位（OAP）和后收缩（AC），这是由研究发现，浓度为 5-12 mM 的 SR 中的 Ca 离子振荡释放可抑制这些 OAP 和 AC，然而，Mg 会增强抽搐收缩，这种作用是由于舒张期期间 SR 中的 Ca 离子振荡释放受到抑制。因此，SR 处的 Ca 振荡似乎减少了 SR 中可用于抽搐的 Ca 量，因为即使在 SR 处也可能存在微观 Ca 振荡。对于正常心肌，上述结果表明，这种振荡可能是调节 SR 中 Ca 量以及细胞 Ca 稳态的重要机制，前提是这些振荡与肌膜的 Ca 挤出功能之间存在联系。在电压钳位的分离肌细胞中，高浓度 (15-25 mM) 的咖啡因可从 SR 中释放 Ca，被发现会诱导脉冲状小脉冲 (20-30 pA 静息电位）内向电流似乎是由细胞内 Ca 激活的，因为 Ca 注入细胞或施加大的去极化会产生强直张力，这些电流是 Na 依赖性的，但可以在细胞内流动。脉冲状的发展表明电流是在肌膜中分布相对较少的位置产生的，最可能的位置是面向观察到的近膜 SR 的位置。电流可能反映了肌膜和 SR 功能耦合的一个方面，我们现在正在使用膜片钳技术在分离的心肌细胞中进一步研究这些电流的性质。电流通过 Ca 激活的非特异性阳离子通道，并对其特性进行了定量分析，该电流有助于 Ca 介导的稳定背景电导，并且不会在整个细胞水平产生脉冲状电事件。