Determination of lithium and rubidium in physiological fluids and tissues of rabbits during the reproductive phase

1. The natural concentrations of lithium and rubidium were determined during the reproductive phase of rabbits by field desorption mass spectrometry. 2. Samples of serum, milk, amniotic fluid and placenta tissue were analysed. 3. The concentration changes in serum during the reproductive phase were between 2.61 and 5.02 micrograms/l for lithium and between 107.78 and 136.28 micrograms/l for rubidium. 4. Correlations between the concentration in maternal serum and bone growth of the fetus as well as the formation of milk were found. 5. Concentrations of 9.30 micrograms/l lithium and 1780.00 micrograms/l rubidium in the milk lead to the assumption that these trace metals are essential for the metabolism of the young rabbit.     

Regulation of fetal Na+/K+-ATPase in rat kidney by corticosteroids

The enzymatic differentiation of various tissues is under hormonal control in the perinatal period. Since the regulation of Na+/K+-ATPase has not been explored prenatally, the aim of this study was to determine the corticosteroid sensitivity of sodium pump maturation in the fetal period. Na+/K+-ATPase activity was both measured in kidney homogenates of fetal rats and localized by in-situ histochemistry. Sodium pump activity was first quantifiable on day 18 of fetal development as 1.4 +/- 0.17 mumol Pi/h per mg protein, and was increased 3.4-times by day 22 of gestation. While the Na+/K+-ATPase activity was the most intense in cortical tubules at an earlier fetal age (18th and 19th day), the reaction product in the medullary tubules increased with fetal age, becoming highly intense on the 21st and 22nd day of gestation. From the 18th to 21st day of fetal development homogenate Na+/K+-ATPase activity increased as a function of chronologic age. While mineralocorticoids were without any effect on Na+/K+-ATPase activity, on the last day of the fetal development, the glucocorticoid dexamethasone proved to be successful in stimulating enzyme activity in corticosteroid-suppressed animals. According to our results, glucocorticoid hormones seem to be operating as an endogenous driving force for sodium pump maturation at the end of fetal development.     

The Effects of Lithium on a Neuronal in Vitro Orcadian Pacemaker

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KC1 concentrations, yielded an increasing magnitude of phase delays with increasing KC1 concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.     

Advantages of rubidium chloride gradients for isopycnic centrifugation of enzymes

The isopycnic centrifugation of beta-amylase and the marker enzyme beta-galactosidase was carried out using four salts viz. rubidium chloride, potassium bromide, potassium acetate and lithium bromide. Lithium bromide inactivated both beta-galactosidase and beta-amylase. The high viscosity of potassium acetate gradients necessitated an extremely long centrifugation time. The density profiles obtained with rubidium chloride gradients were sharper and permitted better resolution than potassium bromide gradients. Both enzymes were stable in rubidium chloride gradients, while potassium bromide inactivated beta-galactosidase, even in the presence of 10 mM 2-mercaptoethanol.     

Cation transport and content in serum-stimulated CHO-773 cells. I. Rapid changes in rubidium and lithium influxes and intracellular sodium content

The cultures of Chinese hamster ovary cells (CHO-K1 clone 773) can be brought to the stationary state with most of cellular populations in G1 phase by growing continuously for 4 days up to the cultural density (10-12) X 10(4) cells/cm2. Upon introduction of fresh Eagle medium with 10% calf serum the cells progress from G1 to S phase for 7-9 hours. It is shown that within the first minutes of serum addition ouabain-sensitive rubidium influx increases, however, lithium influx, which serves a test for passive sodium pathways in the membrane, increases or does not change. No correlation was found between the rubidium influx and intracellular sodium changes, induced by serum. From comparative studies of ouabain-sensitive rubidium influx, lithium influx and intracellular sodium content it is concluded that the increase in intracellular sodium is not responsible for serum-induced Na,K-ATPase activation.     

Embryonic and fetal development in a commercial dam-line genotype

During depopulation of a breeding unit within Swine Graphics Enterprises, extensive data were collected and used to examine relationships among ovulation rate, the pattern of prenatal loss, and placental and fetal development. Groups of Large White x Landrace females (n=447) were slaughtered between day 20-30, 50-55 or 85-90 of gestation, with approximately equal numbers of animals representing gilts and parity 1 (G/P1), parity 2-3 (P2/3), and parity >4 (P4+). Ovulation rate and embryo number were recorded for all animals. With the exception of the G/P1 animals, embryonic and placental weight were recorded for four conceptuses per sow on day 20-30; on day 85-90 two conceptuses per sow were dissected to determine placental and fetal development. Ovulation rate (22.7 +/- 0.2 overall) was higher (P <0.05) in P2/3 (23.6 +/- 0.4) and P4+ (24.7 +/- 0.4) than in G/P1 (20.2 +/- 0.5). Embryonic/fetal survival was 61.8 +/- 2.1% at day 20-30, 50.2 +/- 2.2% at day 50-55 and 48.7 +/- 1.9% at day 85-90 and the number of surviving conceptuses was higher (P <0.05) in the P2/3 sows than in other parity groups. There was no relationship between ovulation rate and number of live embryos at day 20-30 or 85-90. At day 20-30 and 85-90, embryo weight was positively correlated with placental weight, but neither placental weight nor embryonic/fetal weight was correlated with number of viable embryos. A parity by gestation day interaction existed; placental weight for P4+ (3.42 +/- 0.43 g) was less than for P2/3 (7.55 +/- 0.40 g) at day 20-30 (P <0.0001), whereas at day 85-90, placental weight of P2/3 (209.5 +/- 8.5 g) was less (P=0.05) than both G/P1 (235.7 +/- 7.3g) and P4+ (235.4 +/- 7.1 g). At day 85-90, fetal brain weight, relative to body weight (R2=0.61, P <0.0001), and fetal brain:liver weight ratio (R2=0.35; P <0.0001) were negatively related to mean fetal weight, and brain:liver weight ratio showed a trend towards a relationship with number of viable fetuses (P=0.08). Parity also affected brain:liver weight ratio (P=0.01). Clearly, high ovulation rates in the higher parity sows have the potential to cause excessive in utero crowding of conceptuses in the post-implantation period. Even with moderate crowding, increased brain:liver weight ratios in smaller fetuses in late gestation indicate that uterine capacity impacts fetal development as well as the number of surviving fetuses.     

Furosemide-sensitive cation transport in frog skeletal muscle fibers

Furosemide-inhibitable components in unidirectional cation fluxes have been identified in frog skeletal muscle. In sodium loaded muscles, placed in sodium-free rubidium lithium media, furosemide (1 mM) inhibits partially rubidium and lithium influxes as well as potassium and sodium outfluxes. The furosemide-inhibitable components were found to depend on the presence of ouabain. They were greatly diminished in sodium-free magnesium media and were present in chloride-free nitrate containing media. The dependence of furosemide-inhibitable sodium efflux on internal sodium content was also described.     

The transition from HK to LK phenotype in the red cells of newborn genetically LK lambs

Red cells from newborn lambs were separated into different age populations by centrifugation, and cells with fetal hemoglobin (Hb) were distinguished from those with adult Hb by an acid elution technique. Changes were followed during development in rates of K+ transport (active and passive), numbers of Na+/K+ pump sites per cell, cell volumes, and numbers of Lp and L1 antigen sites per cell. These changes were correlated with the percentage of cells with adult hemoglobin. (The Lp and L1 antigens are associated with K+ transport in that specific alloantibody against Lp, anti-Lp, stimulates active transport, and anti-L1 inhibits passive transport.) Active K+ transport decreased during development because of a decline in number of Na+/K+ pumps (from measurements of ouabain binding) and because of an alteration in the affinity of the pumps for intracellular K+ (from kinetic studies in which the intracellular K+ concentration was varied). Cells with fetal Hb had fewer Lp sites and were larger than cells with adult Hb. As transport properties changed, the number of Lp sites increased and continued to increase after all the cells had adult Hb Cells with fetal Hb had as many L1 sites as lamb cells with adult Hb, but the number of L1 sites was less than those found previously for adult sheep. A population of small cells with intermediate K+ concentration and intermediate numbers of Lp sites appeared soon after birth. The various points of evidence suggested that the developmental process leading to cells with adult transport properties was a gradual one and did not coincide precisely with the switch from fetal to adult Hb.     

Effects of caffeine, verapamil, lithium, and KB-R7943 on mechanics and energetics of rat myocardial bigeminies

We examined the effects of pharmacological alteration of Ca2+ sources on mechanical and energetic properties of paired-pulse ("bigeminic") contractions. The fraction of heat release that is related to pressure development and pressure-independent heat release were measured during isovolumic contractions in arterially perfused rat ventricles. The heat released by regular and bigeminic contractions showed two brief pressure-independent components (H1 and H2) and a pressure-dependent component (H3). We used the ratio of active heat (Ha') to pressure-time integral (PtI) and the ratio of H3 to PtI to estimate the energetic cost of muscle contraction (overall economy) and pressure maintenance (contractile economy), respectively. Neither of these ratios was affected by stimulation pattern. Caffeine (an inhibitor of sarcoplasmic reticulum function) significantly decreased mechanical responses and increased the energetic cost of contraction (delta = 101 +/- 12.6%). Verapamil (an L-type Ca2+ channel blocker) decreased pressure maintenance of extrasystolic (delta = 43.4 +/- 3.7%) and postextrasystolic (delta = 37.5 +/- 3.5%) contractions without affecting postextrasystolic potentiation, suggesting that a verapamil-insensitive fraction is responsible for potentiation. The verapamil-insensitive fraction was further studied in the presence of lithium (45 mM) and KB-R7943 (5 microM), inhibitors of the Na+/Ca2+ exchanger. Both agents decreased all mechanical responses, including postextrasystolic potentiation (delta = 67.3 +/- 3.3%), without altering overall or contractile economies, suggesting an association of the verapamil-insensitive Ca2+ fraction to the sarcolemmal Na+/Ca2+ exchanger. The effect of the inhibitors of the Na+/Ca2+ exchanger on potentiation suggests an increased participation of extracellular Ca2+ (and, thus, a redistribution of the relative participation of the Ca2+ pools) during bigeminic contractions in rat myocardium.     

Synergistic hormonal effects on lung maturation in fetal sheep

Cortisol has minimal effects on lung maturation in fetal sheep before 130 days gestation. To test whether there is enhancement of cortisol action by other hormones, cortisol (F), triiodothyronine (T3), epinephrine (E), prolactin (PRL), and epidermal growth factor (EGF), alone or in combination, were infused into fetal sheep for 84 h between 124 and 128 days gestation. A mixture of F + T3 + PRL, but not any combination of two hormones, increased both distensibility [1.71 +/- 0.12 (SE) ml of air/g wet wt at 40 cmH2O, V40] and stability (1.16 +/- 0.09 ml of air per g wet wt at 5 cmH2O, V5) to near full-term values, above values resulting from treatment with F alone (0.91 +/- 0.12 and 0.43 +/- 0.09 ml/g, P less than 0.01). Only F had an effect when given alone, V40 increasing (P less than 0.05). Treatment with F + T3 (0.81 +/- 0.18 ml/g) and F + E (0.77 +/- 0.07 ml/g) increased V5 above values obtained with F alone (P less than 0.05). Alveolar saturated phosphatidylcholine (SPC) was higher after treatment with F + T3 (161 +/- 52 micrograms/g), F + T3 + PRL (156 +/- 53 micrograms/g, P less than 0.05), and F + E (113 +/- 40 micrograms/g, P = 0.07) than after F (12 +/- 3 micrograms/g). We conclude that F, T3, and PRL have a synergistic effect on the development of distensibility and stability of the ovine fetal lung.     

Effect of lithium and rubidium on the ganglionic inhibitory action of norepinephrine

Close intraarterial infusion of lithium chloride (2 and 4 mEq/kg) transiently suppressed evoked postganglionic potentials in the superior cervical ganglion of the cat; lower doses (0.5 and 1 mEq/kg) had no effect on transmission. Potentiation of the ganglionic inhibitory effect of norepinephrine (NE) occurred at plasma concentrations of lithium equivalent to those found to be therapeutic in man. Concurrent administration of lithium (1 mEq/kg) and doxepin (25 mcg/kg) produced greater facilitation of the ganglionic suppressant effect of NE than either lithium or doxepin alone. Rubidium chloride (0.1, 0.5 and 1 mEq/kg) produced temporary blockade of ganglionic transmission; lower doses (0.05 and 0.075 mEq/kg) did not exhibit a ganglioplegic effect. Reduction of the ganglionic inhibitory activity of NE was observed at each dose level of rubidium. Administration of doxepin (25 mcg/kg) immediately after rubidium (0.075 mEq/kg) significantly reduced the inhibitory effect of the cation on NE activity. These results suggest that, in the cat superior cervical ganglion, lithium may block NE uptake and rubidium may promote NE release.     

Inhibition of CLC-2 chloride channel expression interrupts expansion of fetal lung cysts

Normal lung morphogenesis is dependent on chloride-driven fluid transport. The molecular identity of essential fetal lung chloride channel(s) has not been elucidated. CLC-2 is a chloride channel, which is expressed on the apical surface of the developing respiratory epithelium. CLC-2-like pH-dependent chloride secretion exists in fetal airway cells. We used a 14-day fetal rat lung submersion culture model to examine the role of CLC-2 in lung development. In this model, the excised fetal lung continues to grow, secrete fluid, and become progressively cystic in morphology (26). We inhibited CLC-2 expression in these explants, using antisense oligonucleotides, and found that lung cyst morphology was disrupted. In addition, transepithelial voltage (V(t)) of lung explants transfected with antisense CLC-2 was inhibited with V(t) = -1.5 +/- 0.2 mV (means + SE) compared with -3.7 +/- 0.3 mV (means + SE) for mock-transfected controls and -3.3 +/- 0.3 mV (means + SE) for nonsense oligodeoxynucleotide-transfected controls. This suggests that CLC-2 is important for fetal lung fluid production and that it may play a role in normal lung morphogenesis.     

CALCULATIONS OF BIOELECTRIC POTENTIALS : VI. SOME EFFECTS OF GUAIACOL ON NITELLA

Values have been calculated for apparent mobilities and partition coefficients in the outer non-aqueous layer of the protoplasm of Nitella. Among the alkali metals (with the exception of cesium) the order of mobilities resembles that in water and the partition coefficients (except for cesium) follow the rule of Shedlovsky and Uhlig, according to which the partition coefficient increases with the ionic radius. Taking the mobility of the chloride ion as unity, we obtain the following: lithium 2.04, sodium 2.33, potassium 8.76, rubidium 8.76, cesium 1.72, ammonium 4.05, ½ magnesium 20.7, and ½ calcium 7.52. After exposure to guaiacol these values become: lithium 5.83, sodium 7.30, potassium 8.76, rubidium 8,76, cesium 3.38, ammonium 4.91, ½ magnesium 20.7, and ½ calcium 14.46. The partition coefficients of the chlorides are as follows, when that of potassium chloride is taken as unity: lithium 0.0133, sodium 0.0263, rubidium 1.0, cesium 0.0152, ammonium 0.0182, magnesium 0.0017, and calcium 0.02. These are raised by guaiacol to the following: lithium 0.149, sodium 0.426, rubidium 1.0, cesium 0.82, ammonium 0.935, magnesium 0.0263, and calcium 0.323 (that of potassium is not changed). The effect of guaiacol on the mobilities of the sodium and potassium ions resembles that seen in Halicystis but differs from that found in Valonia where guaiacol increases the mobility of the sodium ion but decreases that of the potassium ion.     

Effect of gramicidin A and thallium ions on cation effluxes in frog sartorius muscle

The effluxes of potassium, rubidium, sodium and lithium from the sartorius muscle of Rana temporaria in magnesium-Ringer solution free of sodium and potassium have been studied with the flame-emission technique. The channel-forming antibiotic gramicidin A (2.5 X X10(-7)-1 X 10(-6) mol/l) enhanced the efflux of potassium and rubidium and increased the rate constants of these effluxes. Gramicidin had small if any effect on sodium and lithium effluxes and rate constants. After 60-100 min in a gramicidin-containing medium, the potassium efflux and the corresponding rate constant reached a steady-state level. This steady-state value depended on gramicidin concentration. Effect of gramicidin on both the potassium efflux and the rate constant was partially reversible. Thallium ions (2.5 X 10(-3) and 5 X 10(-3) mol/l) in sodium- and potassium- free magnesium Ringer solution caused a large increase in effluxes of all the cations examined (K+, Rb+ and Na+) both in presence and absence of gramicidin. Possible mechanisms of gramicidin and thallium effects are discussed.     

Diffusion permeability and ultrafiltration-reflection-coefficients of Narand Cl- in the near-term placenta of the sheep

Experiments were performed on unanaesthetized ewes in the last third of pregnancy. Fetuses and ewes had indwelling vascular catheters. In some of the experiments fetal urine was drained to the exterior by means of an indwelling vesicular catheter. Placental diffusion permeabilities were measured with 22Na+ and 36Cl- injected into eight fetuses. Volumes of distribution of Na+ and Cl- in the conceptus were Na+: 548 +/- 24, Cl-: 760 +/- 51 (ml/kg fetal wt +/- SEM). Diffusion permeabilities were Na+: 5.2 X 10(-3) +/- 0.3 X 10(-3), Cl-: 9.8 X 10(-3) +/- 0.9 X 10(-3) (ml.s-1.kg-1 +/- SEM). Ultrafiltration-reflection-coefficients of Na+ and Cl- in the placental exchange barrier were measured 17 times in seven fetuses with vesicular catheters. The transplacental e.m.f. was estimated from these results, on the assumption that the individual reflection-coefficients of Na+ should correlate with those of Cl-. The best estimate was -1.0 mV (fetus negative), and the best estimates of the placental reflection-coefficients were Na+: 0.83 and Cl-: 0.79. There was a reliable negative correlation (P < 0.01) between the calculated reflection-coefficients and the osmolality of the urine secreted by the fetus. This suggested that the concentration of vasopressin in fetal plasma affects the membrane characteristics of the placenta. The mean total osmotic force across the placental barrier of the sheep in these experiments was calculated to be 260 Pa (2 mmHg).     

Impact of periconceptional nutrition on maternal and fetal leptin and fetal adiposity in singleton and twin pregnancies

It has been proposed that maternal nutrient restriction may alter the functional development of the adipocyte and the synthesis and secretion of the adipocyte-derived hormone, leptin, before birth. We have investigated the effects of restricted periconceptional undernutrition and/or restricted gestational nutrition on fetal plasma leptin concentrations and fetal adiposity in late gestation. There was no effect of either restricted periconceptional or gestational nutrition on maternal or fetal plasma leptin concentrations in singleton or twin pregnancies during late gestation. In ewes carrying twins, but not singletons, maternal plasma leptin concentrations in late gestation were directly related to the change in ewe weight that occurred during the 60 days before mating [maternal leptin = 0.9 (change in ewe weight) + 7.8; r = 0.6, P < 0.05]. In twin, but not singleton, pregnancies, there was also a significant relationship between maternal and fetal leptin concentrations (maternal leptin = 0.5 fetal leptin + 4.2, r = 0.63, P < 0.005). The relative mass of perirenal fat was also significantly increased in twin fetal sheep in the control-restricted group (6.0 +/- 0.5) compared with the other nutritional groups (control-control: 4.1 +/- 0.4; restricted-restricted: 4.4 +/- 0.4; restricted-control: 4.3 +/- 0.3). In conclusion, the impact of maternal undernutrition on maternal plasma leptin concentrations during late gestation is dependent on fetal number. Furthermore, we have found that there is an increased fetal adiposity in the twins of ewes that experienced restricted nutrition throughout gestation, and this may be important in the programming of postnatal adiposity.     

Psychomotor excitation caused by beta-endorphin: effect of rubidium and lithium

Effects of lithium and rubidium administered into the cerebral ventricles of conscious cats on psychomotor excitation produced by synthetic human beta-endorphin similarly injected have been investigated. Lithium, but not rubidium, prevented the psychomotor stimulation caused by beta-endorphin. Naloxone, applied intracerebroventricularly, also prevented the psychomotor stimulation produced by this polypeptide. It appears, therefore, that only lithium has a psychotherapeutic value when homeostatic neurohumoral mechanisms are disturbed in the central nervous system by a surplus of beta-endorphin.     

7Li-NMR and FTIR studies of lithium, potassium, rubidium, and cesium complexes with ionophore lasalocid in solution

Lasalocid metal salts were combined with 1 : 1 lithium and 2:2 potassium, rubidium, and cesium to form complexes. The nature of the lasolocid salt complexes was studied in a solid and chloroform by FTIR spectroscopy in the middle and far IR regions. The process of the complexation of lithium was also studied by (7)Li-NMR. In chloroform a 1 : 1 complex of lasalocid and Li(+) ions was formed. Continuous absorption was observed in the far FTIR spectrum of this complex. It indicated large Li(+) polarizability, which was due to fast fluctuations of the Li(+) ions in the multiminima potentials, in the monomeric structure. In the lasalocid salt with the other monovalent cations (K(+), Rb(+), Cs(+)) 2:2 complexes were formed in which the cations showed cation polarizability, which strongly depended on the mass and the radius of the cations.     

Effects of restricting uteroplacental blood flow on concentrations of corticotrophin-releasing hormone, adrenocorticotrophin, cortisol, and prostaglandin E2 in the sheep fetus during late pregnancy.

We have examined the effects of reduced uterine blood flow and prolonged fetal hypoxemia on the temporal relationship between changes in hormones associated with the activity of the pituitary-adrenal axis (corticotrophin-releasing hormone (CRH), adrenocorticotrophin (ACTH), cortisol, and prostaglandin E2 (PGE2) in the ovine fetus at 120-125 days of pregnancy, and we sought evidence for placental secretion of CRH and ACTH during prolonged hypoxemia. Uterine blood flow was reduced by placing an adjustable Teflon clamp around the maternal common internal iliac artery to decrease fetal arterial oxygen saturation from mean values of 59.1 +/- 3.3 to 25.7 +/- 4.6% (+/- SEM, n = 10). There was a transient peak in immunoreactive (IR-) CRH at 1-2 h after reducing uterine blood flow. IR-ACTH rose to peak values at +2 h, then gradually decreased to control level by +12 h. Fetal plasma cortisol and PGE2 concentrations were elevated significantly by +2 and +4 h, respectively, and at 20-24 h. The identity of IR-CRH in fetal plasma and in ovine placental extracts was confirmed by HPLC, but there was no consistent umbilical vein--femoral arterial concentration difference for either IR-CRH or IR-ACTH during normoxemia or hypoxemia. We conclude that a sequence of endocrine changes involving CRH, ACTH, PGE2, and cortisol occurs in the fetus during a prolonged reduction in uterine blood flow. However, we did not obtain evidence, for placental secretion of either CRH or ACTH in response to this manipulation.     

Dependence of ion transport across the plasma membrane on cell culture density. II. Active and passive cation transport during the growth of L cell cultures

Rubidium and lithium influxes as well as intracellular potassium and sodium contents were investigated in L cells during the culture growth. In sparse culture over the cell densities 0.5-3 X 10(4) cells/cm2 ouabain-sensitive rubidium influx is small and ouabain-resistant lithium influx in high. With the increase in culture density up to 4-5 X 10(4) cells/cm2 the active rubidium influx, mediated by ouabain-sensitive component, is enhanced, and ion "leakage" tested by lithium influx is diminished. Simultaneously with the exponential growth of culture the intracellular potassium content is increased and the intracellular sodium content is decreased resulting in the higher K/Na ratio in cell. During the further transition to dense culture and in stationary state (10-17 X 10(4) cells/cm2) the sodium content and lithium influx do not change significantly, but the potassium content is decreased. The decrease in intracellular potassium is correlated with that in the portion of cells in S-phase from 27-30 to 12%. Thus, in transformed cells the density-dependent alterations in membrane cation transport are observed.