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

在豚鼠心室分离的肌肉制剂和单个肌细胞中，研究了与钙离子从肌浆网（SR）振荡释放相关的电和机械活动。在部分去极化的乳头肌中，< β >-肾上腺素能兴奋剂存在的快速刺激（1hz）诱导振荡后电位（OAP）和后收缩（AC），这是由SR中Ca的振荡释放产生的。5-12 mM浓度的Mg离子抑制了这些OAP和AC。然而，Mg增强了抽动收缩，这种效果是由于舒张期SR中Ca的振荡释放受到抑制。因此，SR处的Ca振荡似乎减少了SR中可用于抽搐的Ca量。由于即使在正常心肌中也可能存在微观钙振荡，上述结果表明，如果这些振荡与肌膜的钙挤出功能之间存在联系，则这种振荡可能是调节SR中钙含量以及细胞钙含量的重要机制。在电压夹紧的分离肌细胞中，高浓度（15-25 mM）的咖啡因（从SR中释放Ca）被发现诱导脉冲样的小（静息电位20-30 pA）内向电流。这些电流似乎是由细胞内的钙激活的，因为钙注入细胞或应用产生张力的大去极化增强了它们。这些电流依赖于Na，但可以在Li而不是Na存在的情况下流动。脉冲样的发育表明电流产生于相对较少分布于肌膜的膜部位。观察到的电流可能反映了肌膜和sr功能耦合的一个方面。我们现在正在进一步研究这些电流的性质。用膜片钳技术在分离的肌细胞中也观察到另一种钙激活的电事件。这是通过ca激活的非特异性阳离子通道的电流，并对其性质进行了定量分析。该电流有助于钙介导的稳定背景电导，并且不会在整个细胞水平上产生脉冲样电事件。少

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