运动对人红细胞膜影响的研究——Na~+、k~+—ATP酶活性在运动中的变化

本文重点研究了运动对红细胞膜Na~+、K~+—ATP酶活性的影响,结果提示:运动时若供能不足,将引起细胞渗透压的改变,使红细胞处于不稳定状态,这可能是运动性贫血和筋疲力竭运动后红细胞溶血作用增强的原因之一。     

Verapamil和Mn~（2＋）对缺氧及缺氧复氧心肌细胞内pH的影响

采用荧光探针ＢＣＥＣＦ／ＡＭ结合计算机图像处理技术测定不同时间的缺氧和缺氧复氧单心肌细胞内ｐＨ的变化以及Ｃａ２＋通道阻滞剂Ｖｅｒａｐａｍｉｌ和Ｎａ＋－Ｃａ２＋交换抑制剂Ｍｎ２＋对其的影响。结果显示随着缺氧时间的延长，细胞内ｐＨ也逐渐降低。复氧开始４０ｍｉｎ内，细胞内ｐＨ并未恢复正常。Ｖｅｒａｐａｍｉｌ能减轻缺氧细胞内酸化程度并使其接近正常水平（Ｐ＞０．０５），却未能减轻缺氧复氧细胞内的酸化。无论是缺氧或缺氧复氧心肌细胞，Ｍｎ２＋均未能减轻细胞内的酸化程度。本实验结果提示缺氧和缺氧复氧时细胞内酸化途径并非完全一致。ＶｅｒａＰａｍｉｌ抑制缺氧细胞内ｐＨ下降是其保护缺氧心肌作用的机制之一。     

Amiloride-sensitive Na+/H+ exchange in erythrocytes of patients with NIDDM: a prospective study

Summary Intensive treatment of non-insulin-dependent diabetes mellitus (NIDDM) decreases the rate of microvascular complications, but is associated with increased incidence of cardiovascular morbidity. Enhanced permeability of plasma membranes for sodium (e. g. sodium-hydrogen exchange, NHE) may predict the subset of diabetic patients for whom intensive modalities of treatment are indicated despite their potential risk. However, the accuracy of NHE as a marker of microangiopathy has not been assessed. In this study NHE as initial velocity of amiloride-inhibited H^{+ efflux from erythrocytes (pH} _i 6.35–6.45) into an Na ⁺ -containing medium (pH_o 7.95–8.05), was estimated during 8 years of follow-up in 138 non-microalbuminuric diabetic patients (74 women, 64 men, age 52 ± 4 years) treated with antihyperglycaemic drugs for 14 ± 2 years. Appearance of microalbuminuria, overt proteinuria, azotaemia and retinopathy was assessed annually. Enhanced erythrocyte NHE predicted diabetic nephropathy alone and in association with a family history of hypertension and/or nephropathy with a sensitivity of 86 and 93 %, respectively. No association was found between NHE and retinopathy in NIDDM. It is concluded that assessment of erythrocyte NHE can identify a subset of patients likely to develop renal damage, for whom an aggressive treatment approach might be considered. [Diabetologia (1997) 40: 302–306] Received: 14 June 1996 and in final revised form: 8 November 1996     

C-peptide revisited – new physiological effects and therapeutic implications

Recent studies have demonstrated that replacement of C-peptide to normal physiological concentrations in insulin-dependent diabetic (IDDM) patients on a short-term basis (1–3 h) results in decreased glomerular hyperfiltration, augmented glucose utilization and improved autonomic nervous function. More prolonged administration (1–3 months) of C-peptide to IDDM patients is accompanied by improvements in both renal and autonomic nervous function. Moreover, both in-vitro and in-vivo studies indicate that C-peptide may have a role in the regulation of insulin secretion. The effects of C-peptide may in part be explained by its ability to stimulate Na⁺,K⁺-ATPase activity. In conclusion, the combined findings indicate that C-peptide is a biologically active hormone. The possibility that C-peptide therapy in IDDM patients may be beneficial should be considered.     

Role of skeletal muscle sodium pumps in the adaptation to potassium deprivation

Skeletal muscle is specialized to lose K⁺ to the extracellular fluid during potassium deprivation which buffers the fall in plasma K⁺ concentration. While it remains to be determined whether K⁺ efflux from muscle is altered during K⁺ deprivation, active K⁺ uptake driven by sodium pumps is significantly depressed. The activity of sodium pumps in skeletal muscle does not increase during K⁺ depletion despite elevated intracellular Na⁺, a strong stimulus to increase activity in other cells. There is a decrease in the total pool size of sodium pump αβ heterodimers during potassium deprivation. The α2 (not the α1) sodium pump isoform is specifically decreased and β1 and/or β2 decreases in a muscle-fibre-dependent manner. The specific loss of K⁺ from skeletal muscle is probably a consequence of the fact that the α2 isoform predominates in this tissue. In tissues such as heart, where α2-type pumps are only a minor fraction of the sodium pumps, the activity of the ubiquitous α1 isoform maintains intracellular Na⁺ and K⁺ at control levels, despite the fact that α2 levels decrease by 50%. Analysis of the time course of change in α2 mRNA vs. protein during K⁺ deprivation indicates that there is both a decrease in α2 synthesis and an increase in α2 degradation. The apparent time-lag during potassium deprivation between the early decreases in both surface α2-type sodium pump number (assessed by ³H-ouabain binding) and intracellular K⁺, and the later decrease in total pool size of α2, suggests the hypothesis that there may be an early internalization of α2-type sodium pumps to endosomal pools, followed by a degradation of these internalized pumps, contributing to the decrease in total α2 pool size. The signals mediating this specific response to hypokalemia, and those mediating the restoration of muscle K⁺ stores remain to be determined.     

被动活动对失神经支配骨骼肌超微结构及酶组织化学影响

目的　研究被动活动对失神经支配骨骼肌组织学、超微结构及Na ,K -ATP酶和Ca-ATP酶活性的影响。方法　选用SD大鼠 ,建立双侧下肢失神经支配腓肠肌的实验模型 ,被动活动右下肢 ,观察肌细胞的组织学 ,超微结构及Na,K -ATP酶和Ca -ATP酶活性变化。结果　被动活动侧肢体肌细胞直径及截面积较对照侧下降速度明显减慢 ;被动活动延缓肢体肌细胞的线粒体 ,肌质网退变 ;Na ,K -ATP酶活性下降速度被动活动侧较对照侧慢 2 3 5 3% ;Ca -ATP酶活性下降速度被动活动侧较对照侧慢 13 10 %。结论　被动活动肢体对失神经支配骨骼肌的组织学、超微结构及酶组织化学的各项指标均有保护作用 ,是延缓肌肉萎缩发生与发展的有效手段     

Parathyroid Hormone,Prostaglandin E2, and 1,25-Dihydroxyvitamin D3 Decrease the Level of Na+-Ca2+ Exchange Protein in Osteoblastic Cells

We previously described Na⁺-Ca²⁺ exchange in osteoblastic rat osteosarcoma cells (UMR-106) and demonstrated that Na⁺-dependent Ca²⁺ transport was inhibited by 24-hour treatment of cells with parathyroid hormone (PTH), prostaglandin E₂ (PGE₂), or 1,25(OH)₂D₃. To determine whether this inhibition of Na⁺-Ca²⁺ exchange is at the level of exchanger protein synthesis we have examined exchanger protein levels using immunoblot analysis. UMR-106 cells were treated for 24 hours with or without PTH, PGE₂, or 1,25(OH)₂D₃. Plasma membrane fractions (7500 g) were obtained and proteins were separated by SDS-PAGE, transferred to nylon membranes, and immunoblotted with a polyclonal antibody to the canine cardiac Na⁺-Ca²⁺ exchanger. In rat cardiac membranes, we detected 125 and 75 kD bands, similar to findings for the canine exchanger. In the osteoblastic UMR cell membranes, a specific band was detected at 90 kD that decreased 65% after treatment of cells with PTH. Inhibition by PTH was dose dependent, was maximal with 10⁻⁷ M PTH, and required 16–24 hour treatment time. Similar inhibition was observed after a 24 hour treatment with 10⁻⁶ M PGE₂ or 10⁻⁸ M 1,25(OH)₂D₃. These results demonstrate the presence of a specific protein in UMR cells that cross-reacts with antibody directed against the cardiac Na⁺-Ca²⁺ exchanger. Thus, the previously reported inhibition of Na⁺-Ca²⁺ exchange activity by calcemic agents in osteoblasts appears to be due to regulation of exchanger protein levels in these osteoblastic cells. Received: 5 February 1996 / Accepted: 18 October 1996     

Pharmacological differentiation of synergistic contribution of L-type Ca2+ channels and Na+/H+ exchange to the positive inotropic effect of phenylephrine,endothelin-3 and angiotensin II in rabbit ventricular myocardium

The present study was designed to delineate pharmacologically the role of sarcolemmal L-type Ca²⁺ channels and Na⁺/H⁺ exchange in the positive inotropic effect (PIE) of phenylephrine mediated by alpha-1 adrenoceptors, endothelin (ET) and angiotensin II (Ang II) that stimulate phosphoinositide (PI) hydrolysis in the rabbit ventricular muscle. The PIE of these receptor agonists was compared with the PIE of isoprenaline that accumulates cyclic AMP. For this purpose, we investigated the influence of a Ca²⁺ antagonist, verapamil, and of an inhibitor of Na⁺/H⁺ exchange, 5-(N-ethyl-N-isopropyl) amiloride (EIPA), alone or in combination, on the cumulative concentration-response curve (CRC) for phenylephrine (with 0.3 μM bupranolol), ET-3 and Ang II in isolated right ventricular papillary muscles of the rabbit, which were electrically stimulated at 1 Hz in Krebs-Henseleit solution at 37°C. Verapamil at 0.3 and 1 μM decreased the basal force of contraction to 37.0 ± 4.0% and 13.2 ± 1.1% of the control, respectively, while EIPA even at 10 μM affected the basal force to much less extent and decreased it to 87.0 ± 1.4%. Verapamil (0.3 and 1 μM) and EIPA (1 and 10 μM), when used alone, each significantly attenuated but did not abolish the PIEs induced by phenylephrine, ET-3 and Ang II, while the simultaneous administration of verapamil (1 μM) and EIPA (10 μM) consistently and almost completely inhibited the PIE induced by these receptor agonists. By contrast, the PIE of isoprenaline was retained even in the presence of verapamil and EIPA. These results indicate that both the influx of Ca²⁺ ions through L-type Ca²⁺ channels and activation of Na⁺/H⁺ exchange contribute synergistically to the PIE that is mediated by alpha-1 adrenergic, ET and Ang II receptor agonists, while these mechanisms are not essential for the beta-adrenoceptor-mediated PIE. Received: 20 February 1996 / Accepted: 20 August 1996     

人参皂甙Rb1降低细胞内Ca2+作用的机制

使用荧光探针Fura-2/AM,采用双波长荧光分光光度法观察到,人参皂甙Rb₁(10,50,100μmol·L^-1)能剂量依赖性减少新生鼠脑细胞内钙浓度,并能增加由硫酸亚铁及半胱氨酸所降低的膜流动性,Rb₁(10μmol·L^-1)能使离体大鼠尾动脉去甲肾上腺素量—效曲线右移,最大效应降低;Rb₁(10,100μmol·L^-1)能降低离体鼠基底动脉5-HT所引起的收缩。使用全细胞膜片钳技术发现人参皂甙Rb₁(50,100μmol·L^-1)对钙电流无明显影响;Rb₁在低剂量能增加大鼠突触体Na⁺-K⁺ATPase及Ca²⁺-Mg²⁺ATPase活性。从而揭示Rb₁降低胞内钙含量可能通过增加ATP酶活性而产生。