The roles of aquaporin water channels in the regulation of water transport across the plasma membrane of heart muscle cells.

水在动物细胞质膜上处于热力学平衡状态。当体内或体外渗透压改变时，会发生快速的跨膜水流动，恢复平衡。本研究旨在研究(1)大鼠和豚鼠心肌细胞的渗透压和水运输特性；(2)蛋白磷酸化对肌膜水运输的调节；(3)心肌电生理活动随细胞体积的变化。1.用非等渗液(0.5-4倍正常渗透压)灌流可引起细胞快速和可逆的肿胀或收缩。通过对细胞表面尺寸(20-30μm-S在35℃时)的视频显微镜分析获得的渗透水渗透系数(P_F)比特殊的水运输组织(例如肾小管、红细胞)的渗透系数小10-20倍；其阿累尼乌斯活化能(测量水通量的能量屏障)为…更低的自由水扩散值([大约等于]4千卡摩尔；-1)2.用巯基氧化剂Hg2+&gt；处理后，Pf降低约80%，而巯基还原试剂二硫苏糖醇可拮抗Hg2+&gt；体积敏感离子转运体的抑制剂(Dids、Gd^&lt；3+&Gt；和哇巴因)改变了渗透细胞肿胀的大小，但对P_f.3影响不大。用Forsklin激活腺苷环化酶(FSK)可引起P_f(EC_1；50&GT；0.5μM)的剂量依赖性增加，而腺苷环化酶失活类似物1，9-二脱氧-FSK对P_F_f无明显影响。用磷酸二酯酶抑制剂3-异丁基-1-甲基黄嘌呤和膜通透性二丁酰cAMP模拟FSK的刺激作用。用M受体激动剂Ach或PKA抑制剂H-89处理可拮抗FSK引起的P_F.5升高。这些数据表明，渗透诱导的跨哺乳动物心肌细胞质膜的水通量主要通过水孔，并通过PKA介导的机制进行调节，该机制可能涉及水通道水通道蛋白的磷酸化。水的重新分配改变了细胞体积，从而稀释/浓缩了细胞质成分，并有助于改变电(膜电位和离子电流)和收缩活动。较少

Water is in thermodynamic equilibrium across the plasma membrane of animal cells. When internal or external osmolality is altered, rapid transmembrane water flow occurs and the equilibrium is restored. In this research aimed at investigating (I) osmometric and water-transporting properties of rat and guinea-pig heart cells, (ii) regulation of sarcolemmal water transport by protein phosphorylation and (iii) cell volume-dependent changes in cardiac electrophysiological activities, several lines of new findings were obtained :1. Superfusion with anisosmotic solution (0.5-4 times normal osmolality) caused a rapid and reversible cell swelling or shrinkage. The osmotic water permeability coefficients (P_f) obtained by videomicroscopic analysis of cell surface dimensions (20-30 μm-s^<-1> at 35℃) was 10-20 times smaller than that of specialized water-transporting tissues (e.g., renal tubules, erythrocytes) ; its Arrhenius activation energy, a measure of the energy barrier to water flux, was as … More low as the value for free water diffusion (【approximately equal】4 kcal mol^<-1>).2. Treatment with Hg^<2+>, a sulfhydryl-oxidizing reagent, reduced P_f by 【approximately equal】80%, and the sulfhydryl-reducing reagent dithiothreitol antagonized the inhibitory action of Hg^<2+>. Inhibitors of volume-sensitive ion transports (DIDS, Gd^<3+>, and ouabain) modified the size of osmotic cell swelling but had little effect on P_f.3. Activation of adenylate cyclase with forskolin (FSK) caused a dose-dependent increase in P_f (EC_<50> 0.5 μM), whereas the adenylate cyclase-inactive analogue 1,9-dideoxy-FSK had no significant effect on P_f.4. Stimulatory action of FSK was mimicked by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and the membrane permeable dibutyryl-cAMP. Treatment with the muscarinic agonist Ach or the PKA inhibitor H-89 antagonized the FSK-induced increase in P_f.5. These data indicate that osmotically-induced water flux across the plasma membrane of mammalian heart cells occurs mainly through aqueous pores and is regulated via a PKA-mediated mechanism that may involve phosphorylation of the water channel aquaporin. Redistribution of water changes cell volume, thereby diluting/concentrating the cytoplasmic constituents, and contributes to modified electrical (membrane potential and ionic currents) and contractile activities. Less