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

水在动物细胞的质膜上处于热力学平衡。当内部或外部渗透压改变时，发生快速的跨膜水流并恢复平衡。本研究旨在研究（I）大鼠和豚鼠心脏细胞的渗透压和水转运特性，（ii）蛋白磷酸化对肌膜水转运的调节，（iii）心脏电生理活动的细胞体积依赖性变化，获得了几条新的发现：1。用等渗溶液（0.5-4倍正常渗透压）灌流引起快速和可逆的细胞肿胀或收缩。通过视频显微镜分析细胞表面尺寸（35℃时为20-30 μm-s-1）获得的渗透水渗透系数（P_f）<-1>比专门的水运输组织（例如，肾小管，红细胞）;其Arrhenius活化能，水通量的能量屏障的量度，为 ...更多信息 与自由水扩散的值一样低（[约等于]4 kcal mol/L<-1>）。用巯基氧化剂Hg^2+处理，使P_f降低[约等于] 80%，巯基还原剂二硫苏糖醇拮抗Hg^2+的抑制作用。体积敏感性离子转运抑制剂（DIDS、Gd^&lt;3+&gt;和哇巴因）改变了渗透性细胞肿胀的大小，但对P_f影响不大。用Forskolin（FSK）激活腺苷酸环化酶可引起P_f的剂量依赖性增加（EC_<50>0.5 μM），而腺苷酸环化酶失活类似物1，9-二脱氧-FSK对P_f无显著影响。磷酸二酯酶抑制剂3-异丁基-1-甲基黄嘌呤和膜渗透性二丁酰-cAMP模拟FSK的刺激作用。用毒蕈碱激动剂Ach或PKA抑制剂H-89治疗可拮抗FSK诱导的P_f.5增加。这些数据表明，通过哺乳动物心脏细胞的质膜的水通量主要通过水孔发生，并通过PKA介导的机制，可能涉及磷酸化的水通道水通道蛋白进行调节。水的重新分布改变细胞体积，从而稀释/浓缩细胞质成分，并有助于改变电（膜电位和离子电流）和收缩活动。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