葛根素对再灌注损伤心肌细胞内K^+/Na^+及Ca^(2+)浓度的影响

葛根素具有扩张冠状动脉和脑动脉，降低心肌耗氧量，限制心肌梗死范围的扩大，改善微循环及缓和的降压效果等作用〔１３〕。本研究从大鼠分离的、耐钙心肌细胞模型上观察葛根素对缺氧复氧损伤的保护作用。报告如下。１材料与方法１．１大鼠耐钙心肌细胞的分离：根据Ｆａｒ...

Na^+/K^+-ATPase α-subunit in swimming crab Portunus trituberculatus: molecular cloning, characterization, and expression under low salinity stress

Na^＋/K^＋-ATPases are membrane-associated enzymes responsible for the active transport of Na^＋ and K^＋ ions across cell membranes, generating chemical and electrical gradients. These enzymes＇ α-subunit provides catalytic function, binding and hydrolyzing ATP, and itself becoming phosphorylated during the transport cycle. In this study, Na^＋/K^＋-ATPase α-subunit eDNA was cloned from gill tissue of the swimming crab Portunus trituberculatus by reverse-transcription polymerase chain reaction （RT-PCR） and rapid amplification of eDNA end methods. Analysis of the nucleotide sequence revealed that the eDNA had a full-length of 3 833 base pairs （bp）, with an open reading frame of 3 120 bp, 5＇ untranslated region （UTR） of 317 bp, and 3＇ UTR of 396 bp. The sequence encoded a 1 039 amino acid protein with a predicted molecular weight of 115.57 kDa and with estimated pI of 5.21. It was predicted here to possess all expected features of Na^＋/K^＋-ATPase members, including eight transmembrane domains, putative ATP-binding site, and phosphorylation site. Comparison of arnino acid sequences showed that the P. tritubereulatus α-subunit possessed an overall identity of 75%-99% to that of other organisms. Phylogenetic analysis revealed that this α-subunit was in the same category as those of crustaceans. Quantitative real-time RT-PCR analysis indicated that this α-subunit＇s transcript were most highly expressed in gill and lowest in muscle. RT-PCR analysis also revealed that α-subunit expression in crab gill decreased after 2 and 6 h, but increased after 12, 24, 48, and 72 h. In addition, α-subunit expression in hepatopancreas of crab decreased after 2-72 h. These facts indicated that the crab＇s Na^＋/K^＋-ATPase α-subunit was potentially involved in the observed acute response to low salinity stress.

Ipomoea batatas HKT1 transporter homolog mediates K^+ and Na^+ uptake in Saccharomyces cerevisiae

Soil salinity causes the negative effects on the growth and yield of crops. In this study, two sweet potato （Ipomoea batatas L.） cultivars, Xushu 28 （X-28） and Okinawa 100 （O-100）, were examined under 50 and 100 mmol L-1 NaCI stress. X-28 cultivar is relatively high salt tolerant than O-100 cultivar. Interestingly, real-time quantitative polymerase chain reaction （RT-qPCR） results indicated that sweet potato high-affinity K^＋ transporter 1 （IbHKT1） gene expression was highly induced by 50 and 100 mmol L-1 NaCI stress in the stems of X-28 cultivar than in those of O-100 cultivar, but only slightly induced by these stresses in the leaves and fibrous roots in both cultivars. To characterize the function of IbHKT1 transporter, we performed ion-flux analysis in tobacco transient system and yeast complementation. Tobacco transient assay showed that IbHKT1 could uptake sodium （Na^＋）. Yeast complementation assay showed that IbHKT1 could take up K^＋ in 50 mmol L^-1 K^＋ medium without the presence of NaCI. Moreover, Na^＋ uptake significantly increased in yeast overexpressing IbHKTI. These results showed that IbHKT1 transporter could have K^＋-Na^＋ symport function in yeast. Therefore, the modes of action of IbHKT1 in transgenic yeast could differ from the mode of action of the other HKT1 transporters in class I. Potentially, IbHKT1 could be used to improve the salt tolerance nature in sweet potato.

Arsenic exposure decreases rhythmic contractions of vascular tone through sodium transporters and K^+ channels

Arsenic-contaminated drinking water is a public health problem in countries such as Taiwan, Bangladesh, United States, Mexico, Argentina, and Chile. The chronic ingestion of arsenic-contaminated drinking water increases the risk for ischemic heart disease, cerebrovascular disease, and prevalence of hypertension. Although toxic arsenic effects are controversial, there is evidence that a high concentration of arsenic may induce hypertension through increase in vascular tone and resistance. Vascular tone is regulated by the rhythmic contractions of the blood vessels, generated by calcium oscillations in the cytosol of vascular smooth muscle cells. To regulate the cytosolic calcium oscillations, the membrane oscillator model involves the participation of Ca2+ channels, calcium-activated K+ channels, Na+/Ca2+exchange, plasma membrane Ca2+-ATPase, and the Na+/K+-ATPase. However, little is known about the role of K+ uptake by sodium transporters [Na+/K+-ATPase or Na+-K+-2Cl-(NKCC1)] on the rhythmic contractions.Vascular rhythmic contractions, or vasomotion are a local mechanism to regulate vascular resistance andblood flow. Since vascular rhythmic contractions of blood vessels are involved in modulating the vascular resistance, the blood flow, and the systemic pressure,we suggest a model explaining the participation of the sodium pump and NKCC1 co-transporter in low dose arsenic exposure effects on vasomotion and vascular dysfunction.

Effect of Salinity on the Biosynthesis of Amines in Litopenaeus vannamei and the Expression of Gill Related Ion Transporter Genes

This study examined the effect of salinity on the expression of Na+/K+-ATPase(NKA) α-subunit and vacuolar-type H+-ATPase(V-ATPase) β-subunit gene in the gill of Litopenaeus vannamei. Semi-quantitative reverse transcription-polymerase chain reaction(RT-PCR) assay showed that the expression of NKA α-subunit and V-ATPase β-subunit gene was significantly influenced by salinity. It was found that the NKA activity significantly varied with salinity in time and dose dependent manner; whereas the V-ATPase activity did not. The abundance of NKA α-subunit gene transcript increased rapidly when the salinity decreased from 26 b to 21, and slowly when the salinity decreased from 26 to 31 within the first 24 h. When the salinity decreased from 26 to 21, the transcription of NKA α-subunit gene in gill epithelium was higher at 12 h than that at 0 h, which was consistent with the result of immunoblotting assay of NKA α-subunit. In addition, salinity had a significant time- and dose-dependent effect on the concentration of biogenic amines in both hemolymph and gill. As compared to other parameters, the concentration of dopamine(DA) and 5-hydroxytryptamine(5-HT) varied in different patterns when the salinity decreased from 26 to 21 or increased from 26 to 31, suggesting that DA and 5-HT played different regulatory roles in osmotic adaption and modulation of shrimp when salinity varies.

Changes in growth and osmoregulation during acclimation to saltwater in juvenile Amur sturgeon Acipenser schrenckii

We evaluated the ability of juvenile Amur sturgeon (Acipenser schrenckii) to osmoregulate and grow in saltwater. Hatchery-reared juveniles (mean weight 106.8 g, 5-month old) were transferred from freshwater to 10, 20, and 25 salinity saltwater over a period of 20 d. We measured the growth, serum osmolality, ion concentrations, and Na+/K+-ATPase activity. In addition, we prepared samples of gill tissue to quantify morphological changes in gill ultrastructure. Rearing in up to 25 saltwater for 30 d had no significant effect on growth. Similarly, serum osmolality and ion concentrations were similar to levels reported in other teleosts following acclimation to saltwater. Serum osmolality and Na+, Cl- concentrations increased significantly with the initial increase in salinity. Afterwards, levels tended to stabilize and then decrease. Serum K+ levels did not change during acclimation to saltwater. Gill Na+/K+-ATPase activity increased initially as salinity was increased. However, the activity later decreased and, finally stabilized at 3.7±0.1 μmol Pi/mg·prot·h in 25 saltwater (1.6 times higher than the level in those in freshwater). In fish that were held only in freshwater, the chloride cells were located in the interlamellar regions of the filament and at the base of the lamella. Following acclimation to 25 saltwater for 30 d, the number and size of chloride cells increased significantly. Our results suggest that juvenile Amur sturgeon is able to tolerate, and grow in, relatively high concentrations of saltwater.

A binding-block ion selective mechanism revealed by a Na/K selective channel

Mechanosensitive （MS） channels are extensively stud- ied membrane protein for maintaining intracellular homeostasis through translocating solutes and ions across the membrane, but its mechanisms of channel gating and ion selectivity are largely unknown. Here, we identified the Ynal channel as the Na^＋/K^＋ cation-selec- tive MS channel and solved its structure at 3.8 A by cryo- EM single-particle method. Ynal exhibits low conduc- tance among the family of MS channels in E. coil, and shares a similar overall heptamer structure fold with previously studied MscS channels. By combining structural based mutagenesis, quantum mechanical and electrophysiological characterizations, we revealed that ion selective filter formed by seven hydrophobic methionine （Ynal^Met158） in the transmembrane pore determined ion selectivity, and both ion selectivity and gating of Ynal channel were affected by accompanying anions in solution. Further quantum simulation and functional validation support that the distinct binding energies with various anions to Ynal^Met158 facilitate Na^＋/K^＋ pass through, which was defined as binding-block mechanism. Our structural and functional studies provided a new perspective for understanding the mechanism of how MS channels select ions driven by mechanical force.

Comprehensive screening and selection of okra (Abelmoschus esculentus) germplasm for salinity tolerance at the seedling stage and during plant ontogeny

The okra germplasm was screened for salinity tolerance at the seedling stage and during plant ontogeny. Substantial variation existed in okra for salinity tolerance at the seedling stage. An 80 mmol/L NaCI concentration was suitable for discriminating tolerant and non-tolerant okra genotypes. The pooled ranking of the genotypes, based on individual rankings for each trait （root and shoot length, germination percentage, and relative Na^＋ and K%＋） in individual NaCI concentrations, was effective for selecting tolerant genotypes. Genotypes selected at the seedling stage maintained their tolerance to NaCI during plant ontogeny, suggesting that screening of the germplasm entries and advanced breeding materials for salt tolerance at the seedling stage is effective. Among 39 okra genotypes, five were identified as the most tolerant genotypes and showed potential for use in breeding programs that focus on the development of salt-tolerant, high-yield okra cultivars.