Els W J, Liu X, Helman S I
Department of Molecular and Integrative Physiology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Am J Physiol. 1998 Jul;275(1):C120-9. doi: 10.1152/ajpcell.1998.275.1.C120.
Activation of protein kinase C with phorbol 12-myristate 13-acetate (PMA) caused complex transient perturbations of amiloride-sensitive short-circuit Na+ currents (INa) in A6 epithelia and frog skins that were tissue and concentration dependent. A noninvasive channel blocker pulse method of noise analysis (18) was used to investigate how PMA caused time-dependent changes of apical membrane epithelial Na+ channel (ENaC) single-channel currents, channel open probabilities (Po), and channel densities (NT). In A6 epithelia, 5 and 50 nM PMA caused within 7 min concentration-dependent sustained decreases of Po (approximately 55% below control, 50 nM) and rapid compensatory transient increases of NT within 7 min ( approximately 220% above control, 50 nM), resulting in either small transient increases of INa at 5 nM PMA or small biphasic decreases of INa at 50 nM PMA. In contrast to A6 epithelia, 50 and 500 nM PMA in frog skin caused after a delay of at least 10 min transient increases of NT to approximately 60-70% above control at 30-60 min. Unlike A6 epithelia, Po was increased approximately 15% above control within 7 min and remained within +/-10-15% of control for the duration of the 2-h experiments. Despite differences in the time courses of secondary inhibition of transport in A6 epithelia and frog skin, the delayed downregulation of transport was due to time-dependent decreases of NT from their preelevated levels in both tissues. Whereas Po is decreased within minutes in A6 epithelia as measured by noise analysis or by patch clamp (8), the discrepancy in regulation of NT in A6 epithelia as measured by noise analysis and patch clamp is most likely explained by the inability of on-cell patches formed before treatment of tissues with PMA to respond to regulation of their channel densities.
用佛波醇12 -肉豆蔻酸酯13 -乙酸酯（PMA）激活蛋白激酶C会引起A6上皮细胞和蛙皮中amiloride敏感的短路Na⁺电流（INa）出现复杂的瞬时扰动，这种扰动具有组织和浓度依赖性。采用一种非侵入性通道阻断剂脉冲噪声分析方法（18）来研究PMA如何引起顶端膜上皮Na⁺通道（ENaC）单通道电流、通道开放概率（Po）和通道密度（NT）的时间依赖性变化。在A6上皮细胞中，5 nM和50 nM的PMA在7分钟内引起浓度依赖性的Po持续下降（比对照组50 nM时低约55%），并在7分钟内引起NT快速的补偿性瞬时增加（比对照组50 nM时高约220%），导致5 nM PMA时INa出现小的瞬时增加，或50 nM PMA时INa出现小的双相下降。与A6上皮细胞不同，蛙皮中50 nM和500 nM的PMA在至少延迟10分钟后，在30 - 60分钟时引起NT瞬时增加至比对照组高约60 - 70%。与A6上皮细胞不同，Po在7分钟内比对照组增加约15%，并在2小时的实验过程中保持在对照组的±10 - 15%范围内。尽管A6上皮细胞和蛙皮中转运的二次抑制时间进程存在差异，但转运的延迟下调是由于两种组织中NT从其预先升高的水平出现时间依赖性下降。通过噪声分析或膜片钳测量，A6上皮细胞中的Po在几分钟内下降（8），而通过噪声分析和膜片钳测量的A6上皮细胞中NT调节的差异很可能是由于在用PMA处理组织之前形成的贴壁膜片无法对其通道密度的调节做出反应。
