Panet R, Fixler R, Snyder D, Raz S, Atlan H, Eilam Y, Hasin Y
Department of Medical Biophysics and Nuclear Medicine, Hadassah University Hospital, Jerusalem, Israel.
J Cell Physiol. 1990 Oct;145(1):24-9. doi: 10.1002/jcp.1041450105.
In this study we have characterized the bumetanide-sensitive K+/Na+/Cl- cotransport in cultured rat cardiac myocytes. 1) It carries about 10% of the total K+ influx. 2) It is sensitive to furosemide (Ki0.5 = 10(-6)M) and bumetanide (Ki0.5 = 10(-7)M). 3) It is strongly dependent on the extracellular concentrations of Na+ and Cl-. 4) It carries out influx of both ions, K+ and Na+. A therapeutic concentration of ouabain (10(-7) M) stimulated the bumetanide-sensitive K+ influx (as measured by 86Rb+), in the cultured myocytes, with no effect on the bumetanide-resistant K+ influx, which was mediated mostly by the Na+/K+ pump. Stimulation of the bumetanide-sensitive Rb+ influx by a low ouabain concentration was strongly dependent on Na+ and Cl- in the extracellular medium. A low concentration of ouabain (10(-7) M) was found to increase the steady-state level of cytosolic Na+ by 15%. This increase was abolished by the addition of bumetanide or furosemide. These findings suggest that ouabain, at a low (10(-7) M) concentration, induced its positive inotropic effect in rat cardiac myocytes by increasing Na+ influx into the cells through the bumetanide-sensitive Na+/K+/Cl- cotransporter. In order to examine this hypothesis, we measured the effect of bumetanide on the increased amplitude of systolic cell motion induced by ouabain. Bumetanide or furosemide, added to cultured cardiac myocytes, inhibited the increased amplitude of systolic cell motion induced by ouabain. Neither bumetanide nor furosemide alone has any significant effect on the basal amplitude of systolic cell motion. We propose that stimulation of bumetanide-sensitive Na+ influx plays an essential role in the positive inotropic effect in rat cardiac myocytes induced by low concentration of ouabain.
在本研究中，我们已对培养的大鼠心肌细胞中布美他尼敏感的K⁺/Na⁺/Cl⁻共转运体进行了特性描述。1）它介导约10%的总K⁺内流。2）它对呋塞米（Ki0.5 = 10⁻⁶M）和布美他尼（Ki0.5 = 10⁻⁷M）敏感。3）它强烈依赖于细胞外Na⁺和Cl⁻的浓度。4）它介导K⁺和Na⁺两种离子的内流。治疗浓度的哇巴因（10⁻⁷M）刺激培养心肌细胞中布美他尼敏感的K⁺内流（通过⁸⁶Rb⁺测量），而对主要由Na⁺/K⁺泵介导的布美他尼抵抗性K⁺内流无影响。低浓度哇巴因对布美他尼敏感的Rb⁺内流的刺激强烈依赖于细胞外培养基中的Na⁺和Cl⁻。发现低浓度哇巴因（10⁻⁷M）可使细胞内Na⁺的稳态水平增加15%。添加布美他尼或呋塞米可消除这种增加。这些发现表明，低浓度（10⁻⁷M）的哇巴因通过布美他尼敏感的Na⁺/K⁺/Cl⁻共转运体增加Na⁺流入细胞，从而在大鼠心肌细胞中诱导其正性肌力作用。为了检验这一假设，我们测量了布美他尼对哇巴因诱导的收缩期细胞运动幅度增加的影响。添加到培养心肌细胞中的布美他尼或呋塞米可抑制哇巴因诱导的收缩期细胞运动幅度增加。单独的布美他尼和呋塞米对收缩期细胞运动的基础幅度均无显著影响。我们提出，刺激布美他尼敏感的Na⁺内流在低浓度哇巴因诱导的大鼠心肌细胞正性肌力作用中起重要作用。
