Monteith G R, Blaustein M P
Department of Physiology, University of Maryland School of Medicine, Baltimore MD, USA.
Brain Res. 1998 Jun 8;795(1-2):325-40. doi: 10.1016/s0006-8993(98)00224-8.
The Na+ pump is crucial for the regulation of [Na+]i (the intracellular Na+ concentration) in all cells. Three Na+ pump alpha subunit isoforms, alpha1, alpha2 and alpha3, are expressed in rat hippocampal neurons, and alpha1 and alpha2 are expressed in glia, but the significance of these isoforms is not understood. We exploited the different ouabain affinities of the Na+ pump alpha subunit isoforms in rat (alpha1, low ouabain affinity; alpha2 and alpha3, high ouabain affinity) to probe their possible physiological roles. Low and intermediate doses (1-10 microM) of ouabain and its readily reversible analog, dihydroouabain, altered the spontaneous elevations of [Ca2+]i (the intracellular Ca2+ concentration) in neurons and induced [Ca2+]i transients in glia. Complete inhibition of all Na+ pump isoforms (>/=100 microM ouabain) caused sustained increases in global neuronal [Ca2+]i in rat neuronal/glial hippocampal co-cultures and transient [Ca2+]i increases in surrounding glia. High dose ouabain was also associated with increased [Na+]i and [H+]i in neurons and glia. In contrast, 1 microM ouabain (a concentration that completely inhibits only alpha2 and alpha3) was not associated with sustained increases in global neuronal [Ca2+]i or the sustained derangements in [Na+]i and [H+]i observed with high dose ouabain. Reduction of [K+]o to 1 mM suppressed the spontaneous [Ca2+]i oscillations in neurons and induced Ca2+ transients in some glia; removal of external K+ induced sustained elevation of neuronal [Ca2+]i. These studies indicate that the alpha1 isoform is the 'housekeeper' required for maintenance of the global Na+ gradient. As suggested by their restricted plasmalemmal distribution, the high ouabain-affinity Na+ pump isoforms may have more specific roles in neurons and glia.
钠泵对于调节所有细胞内的[Na⁺]i（细胞内钠离子浓度）至关重要。三种钠泵α亚基同工型，即α1、α2和α3，在大鼠海马神经元中表达，α1和α2在神经胶质细胞中表达，但这些同工型的意义尚不清楚。我们利用大鼠钠泵α亚基同工型不同的哇巴因亲和力（α1，低哇巴因亲和力；α2和α3，高哇巴因亲和力）来探究它们可能的生理作用。低剂量和中等剂量（1 - 10微摩尔）的哇巴因及其易于逆转的类似物双氢哇巴因，改变了神经元中[Ca²⁺]i（细胞内钙离子浓度）的自发升高，并在神经胶质细胞中诱导了[Ca²⁺]i瞬变。完全抑制所有钠泵同工型（≥100微摩尔哇巴因）导致大鼠神经元/神经胶质海马共培养物中全局神经元[Ca²⁺]i持续升高，以及周围神经胶质细胞中[Ca²⁺]i短暂升高。高剂量哇巴因还与神经元和神经胶质细胞中[Na⁺]i和[H⁺]i升高有关。相比之下，1微摩尔哇巴因（仅完全抑制α2和α3的浓度）与全局神经元[Ca²⁺]i的持续升高或高剂量哇巴因所观察到的[Na⁺]i和[H⁺]i的持续紊乱无关。将[K⁺]o降低到1毫摩尔抑制了神经元中自发的[Ca²⁺]i振荡，并在一些神经胶质细胞中诱导了Ca²⁺瞬变；去除细胞外钾离子诱导神经元[Ca²⁺]i持续升高。这些研究表明，α1同工型是维持全局钠梯度所需的“管家”。正如它们局限于质膜分布所暗示的那样，高哇巴因亲和力的钠泵同工型可能在神经元和神经胶质细胞中具有更特定的作用。
