Joshi C, Fernandez J M
Department of Physiology, University of Pennsylvania, Philadelphia 19104-6085.
Biophys J. 1988 Jun;53(6):885-92. doi: 10.1016/S0006-3495(88)83169-2.
We have studied the admittance of patch-clamped mast cells during exocytosis and found that they are adequately described by a four parameter equivalent circuit. On the basis of these measurements, we show that, contrary to current belief, when using a phase sensitive detector, small capacitance changes due to exocytosis or endocytosis should be studied by measuring current 90 degrees out of phase, relative to the component that corresponds to changes in series resistance. We have extended the theory on phase-detectors to include the errors in the estimation of step changes of membrane capacitance. We show that the measured capacitance of a secretory granule can be up to 80% smaller than its true value, during the course of a typical mast cell degranulation. We also describe a software-based phase-detector that simplifies capacitance measurements.
我们研究了胞吐过程中膜片钳记录的肥大细胞的导纳，发现用一个四参数等效电路就能对其进行充分描述。基于这些测量结果，我们表明，与当前的认知相反，当使用相敏探测器时，由于胞吐或胞吞作用引起的小电容变化，应该通过测量相对于与串联电阻变化相对应的分量相位相差90度的电流来进行研究。我们扩展了相敏探测器的理论，以纳入膜电容阶跃变化估计中的误差。我们表明，在典型的肥大细胞脱颗粒过程中，测得的分泌颗粒电容可能比其真实值小80%。我们还描述了一种基于软件的相敏探测器，它简化了电容测量。
