Enhancement of Ca2+-dependent outward current in sheep bladder myocytes by Evans blue dye

 Whole-cell and inside-out patch-clamp techniques were used to assess the action of a well-known dye, Evans blue, on membrane currents in bladder isolated smooth muscle cells from sheep. In whole cells Evans blue dose-dependently increased the outward current by up to fivefold. In contrast, Evans blue had no effect on inward Ca²⁺ current. The effect on outward current was abolished or reduced if the cells were bathed in Ca²⁺-free solution, iberiotoxin (5 × 10^–8 M), or charybdotoxin (5 × 10^–8 M), but was unaffected by externally applied caffeine (5 mM) or in cells exposed to heparin (1 mg/ml) via the patch pipette. In inside-out patches bathed in a Ca²⁺ concentration of 5 × 10^–7 M, Evans blue (10^–4 M) increased the open probability of large-conductance (298-pS) Ca²⁺-dependent K⁺ channels (BK channels), shifting the half maximal-activation voltage by –70 mV. We conclude that Evans blue dye acts as an opener of BK channels. Received: 1 September 1997 / Received after revision: 18 November 1997 / Accepted: 20 November 1997     

Properties of voltage-gated currents of microglia developed using macrophage colony-stimulating factor

Microglia were isolated from a murine neonatal brain cell culture in which their development had been stimulated by supplementation with the macrophage/microglial growth factor macrophage colony-stimulating factor (M-CSF). Using the whole-cell configuration of the patch-clamp technique, voltage-gated membrane currents were recorded from these microglial cells. Hyperpolarization induced inward rectifying K⁺ currents, as described for microglia from untreated cultures. These currents activated negative to the K⁺ equilibrium potential and, with a strong hyperpolarization, displayed time-dependent inactivation. The inactivation was abolished when extracellular NaCl was replaced by N-methyl-d-glucamine (NMG), thereby indicating a partial block of this K⁺ conductance by Na⁺. Inward rectifying currents were also blocked by extracellularly applied Cs⁺ or Ba²⁺. They were slightly diminished following treatment with extracellular tetraethylammonium chloride (TEA) but were not affected by 4-aminopyridine (4-AP). Upon long lasting depolarizing voltage pulses to potentials positive to 0 mV, the cells exhibited a slowly activating H⁺ current which could be reduced by application of inorganic polyvalent cations (Ba²⁺, Cd²⁺, Co²⁺, La³⁺, Ni²⁺, Zn²⁺) as well as by 4-AP or TEA. Based on their kinetics and pharmacological characteristics, both currents detected on M-CSF-grown microglia are suggested to correspond to the inward rectifier and the H⁺ current of macrophages.     

Voluntary consumption of NaCl,KCl, CaCl2, and NH4Cl solutions by 28 mouse strains

Male mice from 28 inbred strains (129P3/J, A/J, AKR/J, BALB/cByJ, BUB/BnJ, C3H/HeJ, C57BL/6J, C57L/J, CAST/Ei, CBA/J, CE/J, DBA/2J, FVB/NJ, I/LnJ, KK/H1J, LP/J, NOD/LtJ, NZB/B1NJ, P/J, PL/J, RBF/DnJ, RF/J, RIIIS/J, SEA/GnJ, SJL/J, SM/J, SPRET/Ei, and SWR/J) were tested with NaCl (75–450 mM), KCl (30–300 mM), CaCl₂ (3–100 mM), and NH4Cl (10–300 mM) solutions using two-bottle preference tests with water as the second choice. For each mineral, there was a wide range of strain variation in solution intakes and preferences. This variation had a substantial genetic component as assessed using heritability estimates. In most cases, the strain means were continuously distributed; however, strains with deviating high or low intakes or preferences were also observed. The associations among the responses to different minerals were only modest, suggesting distinct genetic controls of sodium, potassium, calcium, and ammonium consumption. These results provide a valuable resource for investigators who wish to identify genes involved in the regulation of mineral consumption and balance.     

Normal and homogeneous red blood cell populations over a wide range of hyper-iso-hypotonic media

The volumes of human erythrocytes after rapid and gradual swelling in hypotonic NaCl media were measured using a Coulter Counter Z_B at temperatures of +4°C and +20°C together with potassium leakage, the degree of hemolysis and the ‘returning volume’, i. e., the volume in an isotonic solution to which the cells will return from that in a hypotonic solution. The methodological and systematic errors in the volume measurements were corrected by taking into account the shape dependence of the Coulter Counter and the change in cell population during hemolysis, whereafter the measured cell volume values and the comparison between them become more reliable. The curves for cell volume as an inverse function of osmotic pressure appeared to be non-linear. The slopes were small at first but shoed a rapid increase as the cells approached their maximal volume. The critical hemolytic volume was approx.8% higher at +20°C after both rapid and gradual swelling than at +4°C and approx.4% higher after a gradual swelling as compared with a rapid swelling both at +4°C and +20°C.A decrease in temperature resulted in an increase in the critical osmotic pressure both in rapid and gradual hemolysis, but did not greatly affect the amount of prelytic K⁺ leakage. The critical osmotic pressure was smaller in gradual hemolysis than in rapid hemolysis and the prelytic K⁺ leakage was doubled at both +4°C and +20°C.The shifts in osmotic fragility as a function of temperature may be due to differences in the visco-elastic properties of the cell membrane, but the shifts in osmotic fragility as a function of swelling rate may be connected with differences in potassium leakage and membrane stretch.     

Role of potassium in the regulation of systemic physiological function during exercise

In exercise, potassium (K⁺) is released from contracting muscle predominately through K⁺ channels associated with the repolarization phase of the action potential. Increases in extracellular K⁺ are directly related to increases in metabolic rate and may reach concentrations as high as 8–9 mm in the arterial blood during exhaustive work. Exercise-induced hyperkalaemia has been implicated in several physiological processes, in particular skeletal muscle fatigue, hyperaemia, pressor reflex, arterial chemosensitivity and myocardial stability. There is no direct evidence to show that hyperkalaemia causes muscle fatigue, although raised extracellular [K⁺] may contribute to fatigue during prolonged tetani by depressing the propagation of the action potential down the t-tubule system, thus impairing the release of Ca²⁺ from the sarcoplasmic reticulum. The vasodilating properties of K⁺ may transiently contribute to the early phase of exercise hyperaemia and interact synergistically with other vasoactive substances to cause relaxation by hyperpolarizing K⁺ channels in vascular smooth muscle. Hyperkalaemia has been implicated in the regulation of arterial blood pressure through activation of the muscle afferent reflex where potassium-depolarized C fibres may contribute to a reflex increase in arterial blood pressure. K⁺ can also increase ventilation and the sensitivity of the ventilatory response to hypoxia through direct excitation of the arterial chemoreceptors. Finally, to maintain myocardial electrical stability in exercise, there is a beneficial interaction between raised K⁺ and catecholamines on the heart, so that when they combine, each offsets the other's deleterious effects.     

Comparison of glutamate metabolism in low K (LK), high K and high glutathione (HK/HG) and high K and low glutathione (HK/LG) dog red blood cells

The reasons for the high accumulation of glutamate (Glu), aspartate (Asp) and glutamine (Gin) in high K and high glutathione (HK/HG) dog red blood cells (DRBCs) have been explained as due to enhanced Glu/Asp influxes. However, in our study, Glu/Asp influxes in high K and low glutathione (HK/LG) DRBCs were low, whereas their cellular Asp and Gin contents were high. In low K (LK) DRBCs, there were also other variant cells with high Asp accumulation, but extremely low Glu/Asp influxes. So, the high amino acid accumulation in DRBCs of these new variants might not be due to Glu/Asp influxes. To examine the high accumulation of these amino acids in these variant DRBCs, first, LK and HK/LG DRBCs were classified into two subgroups with their Na-dependent Glu/Asp influxes; one had clear Na-dependent Glu/Asp transport (GAT⁺), and the other failed to have any transport (GAT⁻). The influxes of both Glu and Asp in HK/HG DRBCs were the highest, and the order was HK/HG>LK/GAT⁺>HK/LG/GAT⁺>>LK/GAT⁻=HK/LG/GAT⁻. LK/GAT⁺ cells represented normal DRBCs. Glu/Asp influxes were only trace in both LK/GAT⁻ and HK/LG/GAT⁻ cells, but Glu and Asp concentration was high in HK/LG/GAT⁻ cells whereas Asp concentration was high in LK/GAT⁻ cells. In HK/HG cells, the conversion of Glu into Gin in whole cells was several fold higher than in the other cell groups due to the differing amount of the substrate of glutamine synthetase, Glu, but glutamine synthetase activity itself was not different among these cell groups. Furthermore, glutamine synthetase and glutaminase activities were not different among the cell groups. Therefore, these enzymes were not involved in the high amino acid accumulation.     

Dependency of renal potassium excretion on Na,K-ATPase transport rate

Potassium secretion may depend on the transport rate of Na, K-ATPase in basolateral cell membranes of distal tubular cells. To examine this hypothesis experiments were performed in anaesthetized dogs during inhibition of proximal potassium reabsorption by acetazolamide or mannitol (fractional potassium excretion 1.2-1.4) or additional stimulation of potassium secretion by ethacrynic acid (fractional potassium excretion 2.1). Ouabain in a dose which inhibits 70–80% of the Na, K-ATPase activity reduced fractional potassium excretion to 0.8-0.9 by an effect on distal tubular secretion since potassium transport in the proximal tubules was not affected. Ouabain-sensitive potassium excretion varied in proportion to ouabain-sensitive sodium reabsorption during variation in glomerular nitration rate, even at urinary sodium concentrations exceeding 80 mmol 1^-1. In experiments without ouabain, saline infusion raised potassium excretion and sodium reabsorption until maximal Na, K-ATPase transport rate was reached, as judged from heat production measurements, but not during further increments in urine flow. After inhibition of Na, K-ATPase activity by hypokalaemia, potassium excretion and cortical heat production remained constant over a wide range of urine flow and sodium excretion. We conclude that potassium secretion is dependent on intact Na, K-ATPase activity and is stimulated by sodium delivery to the distal nephron until maximal transport rate of the enzyme is reached.     

Caffeine induces periodic oscillations of Ca2+-activated K+ current in pulmonary arterial smooth muscle cells

The periodic oscillations of outward currents were studied in smooth muscle cells of the rabbit pulmonary artery. The combined stimuli of superfusion with 1 mM caffeine and depolarization of the membrane potential to 0 mV evoked periodic oscillations of outward currents with fairly uniform amplitudes and intervals. The oscillating outward currents induced by caffeine were dependent on intracellular Ca²⁺ concentration ([Ca²⁺]_i) and had a reversal potential near to the equilibrium potential for K⁺. So the oscillating outward currents are carried by K⁺ through Ca²⁺-dependent K⁺ channels (I _K(Ca)), and may reflect the oscillations of [Ca²⁺]_i. The oscillating outward currents were abolished, or their frequency reduced, by lowering external [Ca²⁺], Ca²⁺ channel blockers, or by 1 M ryanodine, indicating that: (1) there is a continuous influx of Ca²⁺ through the plasma membrane at a holding potential of 0 mV; (2) the periodic transient increases of [Ca²⁺]_i are ascribed to the rhythmic release of Ca²⁺ from ryanodinesensitive intracellular store by the mechanism of Ca²⁺-induced Ca²⁺ release (CICR). On the basis of the above results, we simulated the oscillation of [Ca²⁺]_i induced by caffeine, which is known to lower the threshold of CICR. The patterns of peak amplitude histograms of spontaneous transient outward currents (STOC) in the oscillating cells were different from those in non-oscillating cells. The amplitudes of STOC in the latter were more variable than those in the former. The oscillating outward currents were modulated by 1 M forskolin and 1 M sodium nitroprusside, but STOC were little affected. The above differences between STOC and oscillating outward currents suggest that the two currents are activated by the Ca²⁺ originating from different intracellular Ca²⁺ stores which are functionally heterogeneous.     

Genetic variations in five genes involved in the excitement of cardiomyocytes

We provide here 29 genetic variations, including 28 novel ones, in five genes that are potentially involved in the excitement of cardiomyocytes: we found 4 in KCNA10, 2 in KCNK1, 8 in KCNK6, 11 in SLC18A1 (VMAT1), and 4 in SLC6A2 (norepinephrine transporter). We also examined their allelic frequencies in a Japanese population of long QT syndrome-affected and nonaffected individuals. These data would be useful for genetic association studies designed to investigate acquired arrhythmias. Received: May 22, 2001 / Accepted: June 8, 2001     

Pharmacokinetic and pharmacodynamic study of the combination of furosemide retard and triamterene

Summary The pharmacodynamics and pharmacokinetics of the combination of furosemide retard (30 mg)/triamterene (50 mg) were compared with furosemide (30 mg) in 18 healthy male volunteers aged 39.3±6.3 years. After the administration of furosemide the onset of its effect was very rapid, reaching a maximum between 1.5 to 3 h, and followed by rebound after 9 to 10.5 h. In contrast the combination furosemide retard/triamterene showed a protracted course with a duration of effect up to 12 h. The general effect over 12 h of the two preparations was equivalent with respect to the excretion of urine, sodium, chloride and calcium, but the combination caused significantly less excretion of potassium (p0.05) than furosemide. After a lag-phase of 33.9±5.4 min the maximum plasma concentration of furosemide was reached after 3.47±0.66 h, and the elimination half-life was approximately 2 h. After a lag-phase of 33.0±17.8 min the maximum plasma concentration of the main metabolite of triamterene, the OH-TA sulphuric acid ester, was reached after 1.7±0.59 h, and its elimination half-life amounted to 1.25±0.37 h. Because of the sustained release of furosemide from the retard-formulation, its principal pharmacokinetic parameters were better adapted to those of triamterene. The consequences were not only a protracted effect but also an improved electrolyte profile, especially with regard to reduced loss of potassium. In the case of renal insufficiency, however, the potassium level in serum might be increased to an undesirable extent.