脂质过氧化对人红细胞膜脂流动性的影响

研究枯稀过氧化氢/高铁血红素体系所产生的烷基过氧自由基对红细胞的损伤。测定了脂质过氧化的产物——丙二脂的生成,并证明阿魏酸钠对脂质过氧化的抑制。荧光偏振的结果指出,膜脂过氧化以后降低了膜脂的流动性。人红细胞用5DSA和16DSA标记并用ESR检测膜脂流动性,结果表明,序参数S几乎没有发生变化,旋转相关时间τ值的增加证明膜脂过氧化以后,疏水尾部的物理状态发生了改变。经脂质过氧化以后,红细胞膜中的不饱和脂防酸的减少,可能是降低膜脂流动性的原因之一。     

Single point mutations of the sodium channel drastically reduce the pore permeability without preventing its gating

1. Two mutants of the sodium channel II have been expressed inXenopus oocytes and have been investigated using the patch-clamp technique. In mutant E387Q the glutamic acid at position 387 has been replaced by glutamine, and in mutant D384N the aspartic acid at position 384 has been replaced by asparagine.2. Mutant E387Q, previously shown to be resistant to block by tetrodotoxin (Noda et al. 1989), has a single-channel conductance of 4 pS, that can be easily measured only using noise analysis. At variance with the wild-type, the openchannel current-voltage relationship of mutant E387Q is linear over a wide voltage range even under asymmetrical ionic conditions.3. Mutant D384N has a very low permeability for any of the following ions: Cl^–, Na⁺, K⁺, Li⁺, Rb⁺, Ca²⁺, Mg²⁺, NH₄ ⁺ , TMA⁺, TEA⁺. However, asymmetric charge movements similar to the gating currents of the Na⁺-selective wild-type are still observed.4. These results suggest that residues E387 and D384 interact directly with the pathway of the ions permeating the open channel.Abbreviations TTX tetrodotoxin; Na⁺, sodium; K⁺, potassium; - NFR normal frog Ringer - HEPES N-2-hydroxylethyl piperazine-N-2-ethanesulfonic acid - EGTA ethyleneglycol-bis(-amino-ethyl ether) N,N,N',N'-tetra acetic acid - TEA tetraethylammonium - TMA tetramethylammonium;I _g , gating current; , single-channel conductance     

Different modes of electrogenic Na+ absorption in the coprodeum of the chicken embryo: role of extracellular Ca2+

Summary Transepithelial electrogenic Na⁺ transport (I_Na) was investigated in the coprodeum of 20-days-old chicken embryos in Ussing chambers. Short circuit current (I_sc) and transepithelial resistance (R_t) were 14.7±4.8 A · cm^-2 (n=12) and 0.53±0.09 k · cm^-2 (n=12), respectively. I_Na was calculated from changes in I_sc by substitution of mucosal Na⁺ by (N-methyl-d-glucamine) (NMDG). I_sc inversed during Na⁺ removal, and I_Na was found to be 27.8±4.7 A · cm^-2 (n=12). Amiloride (100 mol · l^-1) inhibited only about 60% of I_Na. Analysis of I_sc fluctuations revealed a Lorentzian component in the power density spectrum with a corner frequency of about 57 Hz. This component was not correlated to I_Na, and its origin is still unclear. Removal of mucosal Ca²⁺ increased I_Na about 2.5-fold due to an increase of the amiloride-insensitive component of I_Na in additionally investigated adult tissues. The results clearly show that this is due to a non-selective cation channel with an apparent order of selectivity Cs⁺>Na⁺=K⁺>Rb⁺>Li⁺. The Ca²⁺ concentration required to block 50% of the I_sc was about 18 mol · l^-1. The I _sc ^Ca could also be supressed by other divalent cations such as Mg²⁺ and Ba²⁺. Additionally, an I_Na-linked Lorentzian component occurred which dominated the control spectrum with a significantly higher corner frequency (about 88 Hz). The results indicate that Na⁺ absorption in the coprodeum of the chicken embryo is more complex than in adult hens. However, the Ca²⁺ sensitivity of I_Na is similar to comparable effects described for other epithelia. This possibly reflects the existence of two types of amiloride-insensitive apical cation channels as pathways for Na⁺ absorption, which may be involved to differing degrees in ontogenetic developments of nonselective channels to Na⁺-specific ion channels.Abbreviations DPL direct-linear-plot method - slope of the back-ground noise component - EGTA ethylene glycol-bi(2-amino-ethylether)-N,N,N,N-tetraacetic acid - f frequency - f _c corner frequency of the Lorentzian noise component - G _t transepithelial conductance - HEPES N-hydroxyethylpiperazine-N-ethanesulfonic acid - I _sc short-circuit current - I _Na transepithelial sodium current - I _sc ^Ca Ca²⁺-sensitive short-circuit current - K _m ^Ca Michaelis-Menten constant for Ca²⁺ - K _B power density of the background noise component at f=1Hz - m mucosal - NMDG N-methyl-D-glucamine - R _t transepithelial resistance - s serosal - SEM standard error of mean - S(f) power density of the Lorentzian noise component - S _o plateau value of the Lorentzian noise component     

Steady-state sodium absorption and chloride secretion of colon and coprodeum,and plasma levels of osmoregulatory hormones in hens in relation to sodium intake

Summary The plasma levels of four osmoregulatory hormones and their target ion-transport systems in the lower intestines of the domestic fowl were determined in order to elucidate their interrelationship and their setpoints in relation to NaCl intake. White Plymouth Rock hens were adapted to six intake levels of NaCl (0.20±0.02–24.7±1.9 mmoles Na⁺·kg bw^–1·day^–1) for 6 weeks. The Na⁺ absorption and the Cl^– secretion of colon and coprodeum were characterized in vitro by the effects of hexoses, amino acids, amiloride, and theophylline on the short-circuit current (SCC) and electrical potential difference (PD). The NaCl-conserving system of the adult chicken is set at low intake levels of NaCl as the 80% range (quantitized by non-linear, logistic regression analyses) of the change in the plasma [ALDO], the amiloride-inhibitable Na⁺ absorption of coprodeum and colon ( SCC), occurred from 0.18 to 2.3, from 0.9 to 4.3, and from 1.2 to 7.3 mmoles Na⁺·kg bw^–1·day^–1, respectively. These results demonstrate that the amiloride-inhibitable Na⁺ absorption of coprodcum is more closely linked to plasma [ALDO] than that of colon. The aminoacid-Na⁺ coabsorption of colon increased over exactly the same range of Na⁺ intake as the colonic amiloride-inhibitable Na⁺ absorption decreased, whereas the hexose-Na⁺ coabsorption increased at higher levels of Na⁺ intake, from 2 to 11 mmoles Na⁺·kg bw^–1·day^–1. Both these Na⁺ absorption types had reached their maximums at 24.7 mmoles Na⁺·kg bw^–1·day^–1, whereas the plasma [AVT] and plasma [PRL], although significantly increased, apparently had not; their 80% range of change occurred from 9.9 to 99 mmoles Na⁺·kg bw^–1·day^–1, and the main changes in plasma osmolity were predicted to occur from 5.4 to 107 mmoles Na⁺·kg bw^–1·day^–1. These results suggest that these colonic and hormonal variables conserve osmotically-free water and operate at high NaCl intake. The theophylline-induced colonic Cl^– secretion did not change with NaCl intake, whereas the stimulation of SCC in coprodeum decreased with increasing NaCl intake: The main change occurred between 0 and 3.2 mmoles Na⁺·kg bw^–1·day^–1. Thus, all ion-transport capacity disappears in coprodeum with increased dietary NaCl intake, whereas colon maintains its ion-transport capacity (although the nature of the Na⁺ transport changes). It is suggested that hormones defending the extracellular volume and composition are regulated close to zero input and output of both NaCl and water, regardless of whether they are NaCl conserving or free-water conserving. Therefore, changes in their stable plasma concentrations occur at the extremes of tolerable range of NaCl intake.Abbreviation AA aminoacids - ALDO aldosterone - AMI amiloride - AVT arginine vasotocin - bw body weight - CS corticosterone - HEX hexoses - INDO indomethacin - PD potential difference - PRL prolactin - R resistance - SCC short-circuit current - SD standard deviation - SEM standard error of mean - THEO theophylline     

Effects of prolonged sodium restriction on the morphology and function of rat adrenocortical autotransplants

Summary Regenerated adrenocortical nodules were obtained by implanting fragments of the capsular tissue of excised adrenal glands into the musculus gracilis of rats (Belloni et al. 1990). Five months after the operation, operated rats showed a normal basal blood level of corticosterone, but a very low concentration of circulating aldosterone associated with a slightly increased plasma renin activity (PRA). Regenerated nodules were well encapsulated and some septa extended into the parenchyma from the connective-tissue capsule. The majority of parenchymal cells were similar to those of the zonae fasciculata and reticularis of the normal adrenal gland, while zona glomerulosa-like cells were exclusively located around septa (juxta-septal zone; JZ). In vitro studies demonstrated that nodules were functioning as far as glucocorticoid production was concerned, while mineralocorticoid yield was very low. Prolonged sodium restriction significantly increased PRA and plasma aldosterone concentration, and provoked a marked hypertrophy of JZ, which was due to increases in both the number and average volume of JZ cells. Accordingly, the in vitro basal production of aldosterone and other 18-hydroxylated steroids was notably enhanced. The plasma level of corticosterone, as well as zona fasciculata/reticularis-like cells and in vitro production of glucocorticoids by regenerated nodules were not affected. These findings, indicating that autotransplanted adrenocortical nodules respond to a prolonged sodium restriction similar to the normal adrenal glands, suggest that the relative deficit in mineralocorticoid production is not due to an intrinsic defect of the zona glomerulosa-like JZ, but is probably caused by the impairment of its adequate stimulation under basal conditions. The hypothesis is advanced that the lack of splanchnic nerve supply and chromaffin medullary tissue in regenerated nodules may be the cause of such an impairment.     

The membrane potential modulates the ATP-dependent Ca pump of cardiac sarcolemma

The effect of membrane potential on the activity of the ATP-dependent Ca²⁺ pump of isolated canine ventricular sarcolemmal vesicles were investigated. The membrane potential was controlled by the intravesicular and extravesicular concentration of K⁺, and the initial rates of Ca²⁺ uptake both in the presence and the absence of valinomycin were determined. The rate of Ca²⁺ uptake was stimulated by a inside-negative potential induced in the presence of valinomycin. The valinomycin-dependent stimulation was enhanced by the addition of K⁺ channel blocker, tetraethylammonium ion or Ba²⁺. The electrogenicity of cardiac sarcolemmal ATP-dependent Ca²⁺ pump is suggested from the increase of Ca²⁺ uptake by negative potential induced by valinomycin.     

Sodium-pump activity and its inhibition by extracellular calcium in cardiac myocytes of guinea pigs

Myocardial sodium-pump activity was examined from ouabain-sensitive ⁸⁶Rb⁺ uptake using myocytes isolated from guinea-pig heart. Either sodium loading or the sodium ionophore, monensin, increased ⁸⁶Rb⁺ uptake by over 400%, indicating that the amount of Na⁺ available to the pump is the primary determinant of its activity, and that the sodium pump has a substantial reserve capacity in quiescent myocytes. Moreover, the degree of the above stimulation is markedly higher than corresponding values reported with multicellular preparations, suggesting that diffusion barriers make it impossible to observe the capacity of the sodium pump in the latter preparations. Removal of extracellular Ca²⁺ increased ouabain-sensitive ⁸⁶Rb⁺ uptake, probably by enhancing turnover of the sodium pump rather than increasing availability of Na⁺ to the pump.     

Mineral licks as a sodium source for Isle Royale moose

Summary Natural mineral licks and their use by moose (Alces alces) on Isle Royale National Park, Michigan, were studied during 1982–85. The distribution of known licks suggested that they occurred in association with glacial debris, primarily in the western portions of the island. Moose utilized mineral springs extensively during the spring-summer period, and at least 5 licks were used year-round. During summer, a pronounced diel pattern of moose visitation was apparent, with peak use occurring between 0400–0800 h. Although daytime lick use declined by late June, morning and evening use continued to be relatively high throughout the study period. Peak lick use coincided with leaf-emergence in spring. Moose continued to utilize mineral licks despite the availability of ponds containing aquatic plants. Sodium appeared to be the element attracting moose to licks where they ingest copious amounts of water. Observed sodium ingestion rates (0.35 g/min) at licks indicate that licks provide a more concentrated source of sodium compared to aquatic plants (0.023 g/min). Based on the data presented, we reject the conclusions of earlier workers that aquatic plants constitute the only significant source of sodium for Isle Royale moose.     

Further Studies on the Nature of Postsynaptic Dopamine Uptake and Metabolism in Rat Striatum: Sodium Dependency and Investigation of a Possible Role for Carrier-Mediated Uptake into Serotonin Neurons

The nature of postsynaptic sites involved in the uptake and metabolism of striatal 3,4-dihydroxyphenylethylamine (dopamine, DA) was investigated. The accumulation of [3H]DA (10(-7) M) into slices of rat striatum was found to be greatly dependent (greater than 99%) on the presence of sodium ion in the incubation medium. However, the formation of the [3H]dihydroxyphenylacetic acid (DOPAC) and [3H]homovanillic acid (HVA) was only partially reduced in the absence of sodium (DOPAC, 27% of control; HVA, 47% of control). Inhibition of carrier-mediated DA neuronal uptake with nomifensine (10(-5) M) significantly decreased DA accumulation (18% of control) and [3H]DOPAC formation (62% of control), but enhanced [3H]HVA production (143% of control). Inhibition of the 5-hydroxytryptamine (5-HT, serotonin) neuronal uptake system with fluoxetine (10(-6) M) or selective 5-HT neuronal lesions with 5,7-dihydroxytryptamine (5,7-DHT) had no effect on [3H]DOPAC or [3H]HVA formed from [3H]DA in the presence or absence of nomifensine. These results demonstrate that the uptake and subsequent metabolism of striatal DA to DOPAC and HVA is only partially dependent on carrier-mediated uptake mechanism(s) requiring sodium ion. These data support our previous findings suggesting a significant role for synaptic glial cell deamination and O-methylation of striatal DA. Further, experiments with fluoxetine or 5,7-DHT suggest that 5-HT neurons do not significantly contribute in the synaptic uptake and metabolism of striatal DA.