Pharmacokinetic and Bioequivalent Study of Potassium Chloride Sustained-Release Tablet Under Different Dietary Conditions in Healthy Chinese Subjects

Potassium (K⁺ ) is an endogenous substance that is an essential dietary component. However, the interaction between dietary arrangements and specific effects of dietary K⁺ intake in bioequivalence studies remains unclear. To investigate the influence of dietary arrangement on the bioequivalence of potassium chloride (KCl) sustained-release tablets in healthy Chinese volunteers, the pharmacokinetics of KCl were compared in two open-label, single-center, randomized, two-period crossover studies with different dietary conditions. All volunteers received an oral dose of 6 g of KCl sustained-release tablets under fasting conditions, with different dietary arrangements. Urine samples were collected on baseline days and 48 hours after tablet consumption. Inductively coupled plasma-optical emission spectrometry was used to measure the concentration of K⁺ in the urine samples. Pharmacokinetic parameters were analyzed using Phoenix WinNonlin software in a noncompartmental model. In either clinical trial, no significant differences were observed in the maximal rate of urinary excretion and cumulative urinary excretion from 0 to 24 hours of K⁺ between the reference and test drugs. The bioequivalence studies of both KCl sustained-release tablet formulations were successfully conducted under different dietary conditions.

[Importance of selective A1 agonists for the protection of brain and heart against injuring factors]

Powerful selective A1 agonist N6-cyclopentyladenosine (CPA) effectively protects the brain (upon decapitation) and the heart (upon intoxication by KCl or ethylen glycol tetra acetate (EGTA)) against the action of injuring factors on experimental animals. CPA weakens or removes damages and/or cell death and probably promotes the regeneration of tissue structures and restoration of their functions. Thus, CPA increases the tolerance of the heart and brain with respect to the introduction of two strong toxicants and even upon decapitation. CPA and 5'-N-ethyl carboxamide adenosine (NECA) induce profound hypothermia, which also takes part in the protection. Selective agonists exhibit two different protective effects against injuring factors.

Acute toxicity of sodium nitrate, potassium nitrate, and potassium chloride and their effects on the hemolymph composition and gill structure of early juvenile blue swimmer crabs(Portunus pelagicus Linnaeus, 1758) (Decapoda, Brachyura, Portunidae)

Various nutrients, including K+ and NO3-, are increasingly being discharged into aquatic systems via anthropogenic sources, which may impact marine organisms. The present study was conducted on blue swimmer crab (Portunus pelagicus) early juveniles to determine the acute toxicity of NaNO3, KNO3, and KCl; if a toxicity interaction exists between K+ and NO3-; the hemolymph Na+, K+, and Ca2+ changes; and the gill histopathological alterations following exposure to elevated NaNO3, KNO3, and KCl levels. A total of 20 replicate crabs were exposed to each of the five NaNO3, KNO3, and KCl concentrations for 96 h. After 96 h, the surviving crabs were sampled for hemolymph Na+, K+, and Ca2+ levels and fixed for histological examination of the anterior gills. The 96-h median lethal concentration of NaNO3-N, KNO3-N, KNO3-K, and KCl-K was 3,452, 112, 312, and 356 mg/L, respectively, for early P. pelagicus juveniles. The toxicity of NaNO3-N was significantly less (p < 0.01) than that of KNO3-N. Furthermore, at the same K+ levels, KNO3-K was significantly (p < 0.05) more toxic than KCl-K, indicating a toxicity interaction between K+ and NO3-. Following exposure to elevated KNO3 and KCl levels, the crabs had significantly higher (p < 0.01) hemolymph K+ levels compared to the control. Conversely, following exposure to elevated NaNO3 concentrations, the crabs had significantly higher (p < 0.01) hemolymph Na+ levels but significantly lower (p < 0.01) hemolymph K+ levels. Despite the markedly different hemolymph ionic changes following NaNO3 and KNO3/KCl exposure, the histopathological changes to the anterior gill lamellae of the crabs appeared to be similar, including lamellae swelling, epithelial thickening, pillar cell disruption, necrosis, and distortion.

Aquaporin expression and cell volume regulation in the SV40 immortalized rat submandibular acinar cell line

The amount of aquaporins present and the cellular ability to perform regulatory volume changes are likely to be important for fluid secretions from exocrine glands. In this work these phenomena were studied in an SV40 immortalized rat submandibular acinar cell line. The regulatory cell volume characteristics have not previously been determined in these cells. Cell volume regulation following hyposmotic exposure and aquaporin induction was examined with Coulter counter methodology, radioactive efflux studies, fura-2 fluorescence, and polymerase chain reaction and Western blot techniques. Cell volume regulation was inhibited by the K(+) channel antagonists quinine and BaCl(2) and the Cl(-) channel blocker 5-nitro-2-(3-phenypropylamino)benzoic acid. A concomitant increase in cellular (3)H-taurine release and Ca(2+) concentration was also observed. Chelation of both intra- and extracellular Ca(2+) with EGTA and the Ca(2+) ionophore A23187 did not, however, affect cell volume regulation. Aquaporin 5 (AQP5) mRNA and protein levels were upregulated in hyperosmotic conditions and downregulated upon return to isosmotic solutions, but were reduced by the mitogen-activated ERK-activating kinase (MEK) inhibitor U0126. A 24-h MEK inhibition also diminished hyposmotically induced cell swelling and cell volume regulation. In conclusion, it was determined that regulatory volume changes in this immortalized cell line are due to KCl and taurine efflux. In conditions that increased AQP5 levels, the cells showed a faster cell swelling and a more complete volume recovery following hyposmotic exposure. This response could be overturned by MEK inhibition.

Racial differences in potassium disposal

BACKGROUND

African Americans appear relatively potassium (K(+))-deficient compared with Caucasian Americans whether on unregulated diets or on diets controlled for K(+) content.

METHODS

To determine whether extrarenal K(+) disposal was affected by race, KCl (0.5 mEq/kg in 0.9% saline) was infused over 48 minutes to 12 African American and 12 Caucasian American normotensive, healthy subjects. Identical infusions were administered before and after 10 days of fixed electrolyte intake. In addition to serum K(+), glucose, insulin, renin, and aldosterone were measured in blood, and K(+) and sodium (Na(+)) in urine voided spontaneously during the infusions. Data were analyzed using a two-factor analysis of variance (ANOVA) with repeated measures.

RESULTS

Basal serum K(+) did not differ between races (African American 3.97 +/- 0.06 mEq/L and Caucasian American 3.98 +/- 0.05, P= NS). The rise in serum K(+) during the infusion and the area under the curve of serum K(+) over the 3.5 hours of observation were both greater in African American (African American +0.82 +/- 0.07 mEq/L and Caucasian American +0.61 +/- 0.06, P= 0.001; and African American 6.9 +/- 0.5 units and Caucasian American 5.1 +/- 0.6, P= 0.0012). The 10-day period of controlled intake did not abolish these differences. Aldosterone at baseline was lower and insulin was higher in African Americans at the end of the infusion. Urinary K(+), plasma glucose, and renin levels did not differ between African Americans and Caucasian Americans.

CONCLUSION

Disposal of an intravenous (iv) K(+) load is decreased in African Americans compared with Caucasian Americans, which may reflect decreased Na(+),K(+)-ATPase activity in African Americans in vivo.

Cotinine inhibits catecholamine release evoked by cholinergic stimulation from the rat adrenal medulla

The aim of the present study was to clarify whether cotinine affects the release of catecholamines (CA) from the isolated perfused rat adrenal gland, and to establish the mechanism of its action, in comparison with the response of nicotine. Cotinine (0.3-3 mM), when perfused into an adrenal vein for 60 min, inhibited CA secretory responses evoked by ACh (5.32 mM), DMPP (a selective neuronal nicotinic agonist, 100 microM for 2 min) and McN-A-343 (a selective muscarinic M1-agonist, 100 microM for 2 min) in dose- and time-dependent manners. However, cotinine did not affect CA secretion by high K+ (56 mM). Cotinine itself also failed to affect basal CA output. Furthermore, in the presence of cotinine (1 mM), CA secretory responses evoked by Bay-K-8644 (an activator of L-type Ca2+ channels, 10 microM) and cyclopiazonic acid (an inhibitor of cytoplasmic Ca2+-ATPase, 10 microM) were relative time-dependently attenuated. However, nicotine (30 microM), given into the adrenal gland for 60 min, initially rather enhanced CA secretory responses evoked by ACh and high K+, followed by the inhibition later, while it time-dependently depressed the CA release evoked by McN-A-343 and DMPP. Taken together, these results suggest that cotinine inhibits greatly CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does fail to affect that by the direct membrane-depolarization. It seems that this inhibitory effect of cotinine may be exerted by the cholinergic blockade, which is associated with blocking both the calcium influx into the rat adrenal medullary chromaffin cells and Ca2+ release from the cytoplasmic calcium store. It also seems that there is a big difference in the mode of action between cotinine and nicotine in the rat adrenomedullary CA secretion.

Glutamatergic transmission in the rat brain and gravitational stress

The effects of hypergravity stress on L-[14C]-glutamate release from synaptosomes obtained from the rat brain and on the kinetic parameters of high-affinity glutamate transport activity were investigated. We found that hypergravity stress affected only the Ca(2+)-dependent component of L-[14C]-glutamate release. It did not modify the transporter affinity, but the maximum rate of uptake dropped from 12.5 +/- 3.2 to 5.6 +/- 0.9 nmol/min/mg of protein (in control rats and in animals subjected to hypergravity, respectively).

Acute Limb Ischemia does not Facilitate but Inhibits Norepinephrine Release from Muscle Sympathetic Nerve Endings in Anesthetized Rabbit

Although myocardial ischemia is associated with regional cardiac sympathetic nerve deterioration, it remains unknown whether acute hindlimb ischemia impairs muscle sympathetic nerve function. In the study presented here we implanted dialysis probes in the adductor muscle of anesthetized rabbits and measured dialysate norepinephrine levels as an index of muscle sympathetic nerve activity. Acute hindlimb ischemia was induced by injection of microspheres and occlusion of the common iliac artery. Dialysate norepinephrine levels decreased from 19.3 +/- 3.5 pg/ml at control to 9.4 +/- 3.7 pg/ml at 30 min of ischemia and further to 1.7 +/- 0.2 pg/ml at 75 min of ischemia. During acute hindlimb ischemia, baroreflex (bilateral carotid occlusion) and high potassium level-induced norepinephrine response was inhibited, but tyramine-induced norepinephrine response was preserved. In conclusion, acute hindlimb ischemia caused decreases in dialysate norepinephrine levels. This reduction may be mediated by an impairment of axonal conduction and/or of norepinephrine releasing function at skeletal muscle sympathetic nerve endings.

Performance of fungi in low temperature and hypersaline environments

During the past ten years we have observed a broad array of stress capabilities in common fungi including ability to grow in aqueous ammonia and other alkaline solutions, in acids, in the presence of heavy metals, and in various salt media at low temperature. This report is concerned primarily with (a) the performance of Aspergillaceae in a variety of saturated salts, (b) distinctive roles for K+ and Rb+ ions, and (c) the lowest temperatures at which growth in nutrient brines has been observed, namely 267 degrees K in as little as 14 days. We also describe a novel solid medium based upon gelatin, glycerol and water in which fungal cultures growing at 248 degrees K can be directly examined under oil-immersion magnification. The performance capabilities of the fungi show that tolerance or adaptability to harsh and extreme physical-chemical environments cannot be considered a unique feature of prokaryotic life forms. Salt flats, brine pools and other natural hypersaline environments have long been recognized as real ecological niches harboring a range of biota from pseudomonad bacteria and green algae to specialized crustaceans. A notable omission in this ecological record is the fungi, although the group is known to include marine forms.

Anion-dependent Mg2+ influx and a role for a vacuolar H+-ATPase in sheep ruminal epithelial cells

The K+-insensitive component of Mg2+ influx in primary culture of ruminal epithelial cells (REC) was examined by means of fluorescence techniques. The effects of extracellular anions, ruminal fermentation products, and transport inhibitors on the intracellular free Mg2+ concentration ([Mg2+]i), Mg2+ uptake, and intracellular pH were determined. Under control conditions (HEPES-buffered high-NaCl medium), the [Mg2+]i of REC increased from 0.56 +/- 0.14 to 0.76 +/- 0.06 mM, corresponding to a Mg2+ uptake rate of 15 microM/min. Exposure to butyrate did not affect Mg2+ uptake, but it was stimulated (by 84 +/- 19%) in the presence of CO2/HCO(-)3. In contrast, Mg2+ uptake was strongly diminished if REC were suspended in HCO(-)3-buffered high-KCl medium (22.3 +/- 4 microM/min) rather than in HEPES-buffered KCl medium (37.5 +/- 6 microM/min). After switching from high- to low-Cl- solution, [Mg2+]i was reduced from 0.64 +/- 0.09 to 0.32 +/- 0.16 mM and the CO2/HCO(-)3-stimulated Mg2+ uptake was completely inhibited. Bumetanide and furosemide blocked the rate of Mg2+ uptake by 64 and 40%, respectively. Specific blockers of vacuolar H+-ATPase reduced the [Mg2+]i (36%) and Mg2+ influx (38%) into REC. We interpret this data to mean that the K+-insensitive Mg2+ influx into REC is mediated by a cotransport of Mg2+ and Cl- and is energized by an H+-ATPase. The stimulation of Mg2+ transport by ruminal fermentation products may result from a modulation of the H+-ATPase activity.

Influence of K-Cl cotransporter activity on activation of volume-sensitive Cl- channels in human osteoblasts

The whole cell recording mode of the patch-clamp technique was used to study the effect of hypotonic NaCl or isotonic high-KCl solution on membrane currents in a human osteoblast-like cell line, C1. Both hypotonic NaCl or isotonic high-KCl solution activated Cl- channels expressed in these cells as described previously. The reversal potential of the induced Cl- current is more negative when activated through hypotonic NaCl solution (-47 +/- 5 mV; n = 6) compared with activation through isotonic high-KCl solution (-35 +/- 3 mV; n = 8). This difference can be explained by an increase in intracellular [Cl-] through the activity of a K-Cl cotransporter. Potassium aspartate was unable to activate the current, and furosemide or DIOA suppressed the increase in Cl- current induced by isotonic high-KCl solution. In addition, we used the polymerase chain reaction to demonstrate the presence of KCC1-KCC4 mRNA in the osteoblast-like cell line. From these results, we conclude that human osteoblasts express functional K-Cl cotransporters in their cell membrane that seem to be able to induce the indirect activation of volume-sensitive Cl- channels by KCl through an increase in the intracellular ion concentration followed by water influx and cell swelling.

Design and evaluation of sustained release microspheres of potassium chloride prepared by Eudragit

The aim of the present work was to prepare and evaluate the sustained release of potassium chloride formulations. Eudragit RS and/or RL loaded with potassium chloride microspheres were prepared by a solvent evaporation method. The effect of sustained release of Eudragit microspheres was evaluated by an in vitro dissolution test and in vivo oral absorption study, and the results were compared to a commercial product (Slow-K). The results showed that Eudragit microspheres loaded with potassium chloride can be easily prepared and satisfactory results obtained considering the size distribution and shapes of microspheres by incorporating aluminum stearate. The encapsulation efficiency and loading capacity were about 84-90% and 27%, respectively. Moreover, the Eudragit RS (30-45 mesh) and Eudragit RS/RL (20-30 mesh) microspheres showed a similar sustained release effect of commercial product via in vitro dissolution and in vivo oral absorption study.

Facilitated transport of sodium or potassium chloride across vesicle membranes using a ditopic salt-binding macrobicycle

A synthetic receptor, with an ability to bind sodium or potassium chloride as a contact ion-pair, is shown to effectively transport either salt across vesicle membranes. Significant transport is observed even when the transporter: phospholipid ratio is as low as 1:2500. Chloride efflux from unilamellar vesicles is monitored using a chloride selective electrode. Mechanistic studies indicate that the facilitated efflux is due to the uncomplexed transporter diffusing into the vesicle and the transporter-salt complex diffusing out. Vesicle influx experiments are also reported, where the facilitated influx of chloride and sodium ions into vesicles is observed directly by 35Cl and 23Na NMR, respectively.

Effects of concentration boundary layers in a transport of electrolyte solutions through horizontal mounted polymeric membrane

The results of experiment of diffusive transmembrane transport in a single-membrane osmotic-diffusive electrochemical cell were presented. In all experiments one of the vessels was filed with pure water, and the second one--with aqueous potassium chloride solution in aqueous ammonia solutions of constant concentration. The flux of potassium chloride was assigned according to the following measure procedure. In a first step we assigned the time dependence of potassium chloride flux in conditions of uniform mechanically stirred solution with speed of 500 rpm. In a second step those characteristics were assigned in conditions of mechanically unstirred solution. Each experiment was made for two configurations of gravitational membrane system: (i) with the water in a vessel above the membrane and solution below it (configuration A) (ii) with the solution in a vessel above the membrane and water below it (configuration B). Taking under the consideration the values of potassium chloride flux in steady state for different solution concentration of the same substances and the same configurations of membrane system, the dependencies of potassium chloride flux from the solution concentration differences were made appropriately. On the base of those experiments the solute flux concentration boundary layers effects (jCBLE) were counted. Moreover it was shown that single-membrane osmotic-diffusive electrochemical cell has rectifier and amplifying of diffusive flow features. The coefficients, appropriately, of asymmetry and amplification of diffusive flux are the measurements of those features.

In vitro and in vivo evaluation of potassium chloride sustained release formulation prepared with saturated polyglycolyed glycerides matrices

The aim of the present work was to evaluate the effect of sustained release of potassium chloride semi-solid matrices prepared with different kinds and added amounts of Gelucires by the in vitro dissolution test and in vivo oral absorption study, and compared with a commercial product (slow-K). The results indicating that the release rates of potassium from experimental formulations were dependent on the type of semi-solid matrices (Gelucires). The higher the melting point of the Gelucires was incorporated, the slower release rate of the active substance was observed. Moreover, the values of similarity factor of Formulae F05 and F09 versus the reference in three kinds of dissolution medium (f(2)) were higher than 50, indicating that these experimental formulations had similar sustained release effects to the reference (slow-K) in dissolution test. In vivo study, the cumulative amount (mEq) of potassium excreted curve and the excretion rate curve of F05 and F09 were found to be similar to that of slow-K, and there were no significant differences (P > 0.05) in the maximum excretion rate and the mean time to reach the maximum rate between formulations and slow-K, indicating that the potassium chloride sustained release dosage form could be prepared using the Gelucires as lipid excipients.

Funipuncture for fetocide in late termination of pregnancy

The most widely used method for fetocide in late termination of pregnancy for fetal abnormalities (TOPFA) consists of injecting of potassium chloride (KCl) into the fetal heart and is likely to be painful after 22 weeks of gestation. We studied ten consecutive women undergoing TOPFA between 22 and 38 weeks. This technique for fetocide consisted of a single umbilical vein puncture under ultrasound guidance with injections of sufentanil 5 microg followed by KCl 2 g. No electrocardiographic modifications could be observed and maternal plasma potassium levels did not show any significant variation throughout the procedure. Fetal umbilical phlebotomy for fetal analgesia followed by fetocide therefore appears to be a safe procedure for the mother and allows the fetus to die without pain when late termination of pregnancy (TOP) is indicated.

[Relative bioavailability of effervescent tablet of potassium chloride in healthy volunteers]

AIM

To probe the approach by which the pharmacokinetics and relative bioavailability of endogenous medicinal substances can be studied.

METHODS

A randomized three-crossover study was performed in 18 healthy male volunteers. In two of the three study periods, a single 2 g dose of either effervescent tablet or common tablet of potassium chloride was administered; whereas in one of three periods no drug treatment was given to allow the nondrug-related (endogenous) potassium in urine to be determined. In each period the urine samples were collected at the following intervals: 0-2, 2-4, 4-6, 6-8, 8-10, 10-12, 12-24, 24-48 h after dose. Urine potassium was determined and the cumulative urine potassium-time data were fitted to a one-compartment model with first-order absorption. Bioavailability was represented by cumulative amount of potassium excreted in urine during 48 hours after drug administration and the bioequivalence of the two formulations was evaluated by analysis of variance and two one-sided t-test.

RESULTS

The pharmacokinetic parameters were as follows: effervescent tablet T1/2 ke = (6 +/- 5) h, T1/2 ka = (0.08 +/- 0.08) h, ku = (0.09 +/- 0.04) h-1, Xmax/f = (18 +/- 8) mmol; common tablet T1/2 ke = (8 +/- 5) h, T1/2 ka = (0.11 +/- 0.11) h, ku = (0.07 +/- 0.04) h-1, Xmax/f = (18 +/- 8) mmol. Relative bioavailability of effervescent tablet was 97.5% +/- 15.2% compared with common tablet.

CONCLUSION

The two formulations were of bioequivalence. The methods used in this study might be applicable to other similar studies involving endogenous medicinal substances.

A cyclic AMP-regulated negative feedforward system for neuritogenesis revealed in a neuroblastomaxglioma hybrid cell line

We examined the role of second messengers during the neuritogenesis that accompanies neuronal differentiation in a neuroblastomaxglioma hybrid cell line (NG108-15). NG108-15 cells extended neurites after treatment with dibutyryl cyclic AMP. This dibutyryl cyclic AMP treatment evoked the synthesis of voltage-dependent Ca(2+) channel proteins in the cells. The number of neurites was decreased by Ca(2+) influx under condition of high K(+). Interestingly, the increase of neurites stimulated by dibutyryl cyclic AMP and the decrease of neurites caused by high K(+) were both reversible. This is the first study to demonstrate that cyclic AMP regulates a negative feedforward system for neuritogenesis, which links with Ca(2+) signaling. Such a dual role of cyclic AMP may play an important part in precise neurite targeting.

Model of ionic transport for bovine ciliary epithelium: effects of acetazolamide and HCO

The possible existence of transepithelial bicarbonate transport across the isolated bovine ciliary body was investigated by employing a chamber that allows for the measurement of unidirectional, radiolabeled fluxes of CO2 + HCO. No net flux of HCO was detected. However, acetazolamide (0.1 mM) reduced the simultaneously measured short-circuit current (I(sc)). In other experiments in which (36)Cl- was used, a net Cl- flux of 1.12 microeq. h(-1). cm(-2) (30 microA/cm(2)) in the blood-to-aqueous direction was detected. Acetazolamide, as well as removal of HCO from the aqueous bathing solution, inhibited the net Cl- flux and I(sc). Because such removal should increase HCO diffusion toward the aqueous compartment and increase the I(sc), this paradoxical effect could result from cell acidification and partial closure of Cl- channels. The acetazolamide effect on Cl- fluxes can be explained by a reduction of cellular H+ and HCO (generated from metabolic CO2 production), which exchange with Na+ and Cl- via Na+/H+ and Cl-/HCO exchangers, contributing to the net Cl- transport. The fact that the net Cl- flux is about three times larger than the I(sc) is explained with a vectorial model in which there is a secretion of Na+ and K+ into the aqueous humor that partially subtracts from the net Cl- flux. These transport characteristics of the bovine ciliary epithelium suggest how acetazolamide reduces intraocular pressure in the absence of HCO transport as a driving force for fluid secretion.

Glycine betaine accumulation, ionic and water relations of red-beet at contrasting levels of sodium supply

Exposure of plants to sodium (Na) and salinity may increase glycine betaine accumulation in tissues. To study this, red-beet cvs. Scarlet Supreme and Ruby Queen, were grown for 42 days in a growth chamber using a re-circulating nutrient film technique with 0.25 mmol/L K and either 4.75 mmol/L (control) or 54.75 mmol/L (saline) Na (as NaCl). Plants were harvested at weekly intervals and measurements were taken on leaf water relations, leaf photosynthetic rates, chlorophyll fluorescence, chlorophyll levels, glycine betaine levels, and tissue elemental composition. Glycine betaine accumulation increased under salinity and this accumulation correlated with higher tissue levels of Na in both cultivars. Na accounted for 80 to 90% of the total cation uptake under the saline treatment. At final harvest (42 days), K concentrations in laminae ranged from approximately 65-95 micromoles g-1 dry matter (DM), whereas Na in shoot tissue ranged from approximately 3000-4000 micromoles g-1. Leaf sap osmotic potential at full turgor [psi(s100)] increased as lamina Na content increased. Glycine betaine levels of leaf laminae showed a linear relationship with leaf sap [psi(s100)]. Chlorophyll levels, leaf photosynthetic rates, and chlorophyll fluorescence were not affected by Na levels. These results suggest that the metabolic tolerance to high levels of tissue Na in red-beet could be due to its ability to synthesize and regulate glycine betaine production, and to control partitioning of Na and glycine betaine between the vacuole and the cytoplasm.

Regulation of P2X(7) nucleotide receptor function in human monocytes by extracellular ions and receptor density

P2X receptors function as ATP-gated cation channels. The P2X(7) receptor subtype is distinguished from other P2X family members by a very low affinity for extracellular ATP (millimolar EC50) and its ability to trigger induction of nonselective pores on repeated or prolonged stimulation. Previous studies have indicated that certain P2X(7) receptor-positive cell types, such as human blood monocytes and murine thymocytes, lack this pore-forming response. In the present study we compared pore formation in response to P2X(7) receptor activation in human blood monocytes with that in macrophages derived from these monocytes by in vitro tissue culture. ATP induced nonselective pores in macrophages but not in freshly isolated monocytes when both cell types were identically stimulated in standard NaCl-based salines. However, ion substitution studies revealed that replacement of extracellular Na+ and Cl- with K+ and nonhalide anions strongly facilitated ATP-dependent pore formation in monocytes. These ionic conditions also resulted in increased agonist affinity, such that 30-100 microM ATP was sufficient for activation of nonselective pores by P2X(7) receptors. Comparison of P2X(7) receptor expression in blood monocytes with that in macrophages indicated no differences in steady-state receptor mRNA levels but significant increases (up to 10-fold) in the amount of immunoreactive P2X(7) receptor protein at the cell surface of macrophages. Thus ability of ATP to activate nonselective pores in cells that natively express P2X(7) receptors can be modulated by receptor subunit density at the cell surface and ambient levels of extracellular Na+ and Cl-. These mechanisms may prevent adventitious P2X(7) receptor activation in monocytes until these proinflammatory leukocytes migrate to extravascular sites of tissue damage.

A fast and simple screening test to search for specific inhibitors of the plasma membrane calcium pump

No specific inhibitors of the plasma membrane Ca(2+) pump have been found to date, limiting research on the particular contribution of this pump to the Ca(2+) homeostasis of animal cells. The search for Ca(2+) pump inhibitors may have been hampered by the lack of an efficient screening method to measure pump activity that would provide an alternative to the lengthy and costly adenosine triphosphatase or Ca(2+)-flux measurements. We propose here a novel screening method in which Ca(2+) pump inhibition is translated into easily measurable cell dehydration. Intact human red cells, suspended in Ca(2+)-containing, low-K(+) buffers were exposed to sequential additions of (1) ionophore A23187 (t = 0) to load the cells with Ca(2+); (2) CoCl(2) (t = 1 minute) to block ionophore-mediated Ca(2+) transport and to allow complete extrusion of the Ca(2+) load by the pump in less than 5 minutes; and (3) NaSCN (t = 6 minutes) to accelerate cell dehydration via Ca(2+)-sensitive K(+) channels when the Ca(2+) load is retained as a result of Ca(2+) pump inhibition. Samples were taken at 10 to 25 minutes after ionophore addition and delivered into hypotonic media containing about 45 mmol/L NaCl. Non-dehydrated cells-with normal, uninhibited pumps-instantly underwent lysis, whereas dehydrated cells-with inhibited pumps-resisted lysis, resulting in translucent or opaque samples, respectively, which were quantifiable by light-absorption measurements. Vanadate was used as a test substance to assess the effect of putative pump inhibitors. This method offers a cost-efficient and easily automated alternative for testing large numbers of natural or synthetic agents.

A model for predicting chloride concentrations in river water in a relatively unpolluted catchment in north-east Scotland

The River Dee is an oligotrophic soft water system, in the NE of Scotland, with a catchment area of approximately 2100 km2. The river rises in the Cairngorm Mountains and enters the North Sea at Aberdeen, approximately 140 km from its source. Water chemical quality data was collected every 2 weeks over 12 months for 59 sites distributed throughout the catchment. River water chloride concentrations increased significantly from west to east. In depth investigation of the relationship with distance from the coast revealed the significant difference in spatial distribution of river water chloride concentrations between upland and lowland/agricultural areas, suggesting the possible importance of agricultural practices to streamwater chloride concentrations. Thirty of the sample sites are independent and have been used to develop a simple model for prediction of streamwater Cl- concentration throughout the catchment. The model has been validated using data from the remaining sub-catchments. The model shows that mean Cl- concentration may be reliably predicted from distance from the coast and the percentage of improved grassland and arable land cover in each sub-catchment (r2 = 0.98). It is postulated that the land use effects may be partly due to the evolved link between landuse and catchment altitude characteristics, rather than just the direct effect of applied potassium chloride fertiliser on agricultural land. It was noted that there was insufficient forestry within the River Dee Catchment to reliably include % forest cover in the model.

K(+)/Na(+) antagonism at cytoplasmic sites of Na(+)-K(+)-ATPase: a tissue-specific mechanism of sodium pump regulation

Tissue-distinct interactions of the Na(+)-K(+)-ATPase with Na(+) and K(+), independent of isoform-specific properties, were reported previously (A. G. Therien, N. B. Nestor, W. J. Ball, and R. Blostein. J. Biol. Chem. 271: 7104-7112, 1996). In this paper, we describe a detailed analysis of tissue-specific kinetics particularly relevant to regulation of pump activity by intracellular K(+), namely K(+) inhibition at cytoplasmic Na(+) sites. Our results show that the order of susceptibilities of alpha(1) pumps of various rat tissues to K(+)/Na(+) antagonism, represented by the ratio of the apparent affinity for Na(+) binding at cytoplasmic activation sites in the absence of K(+) to the affinity constant for K(+) as a competitive inhibitor of Na(+) binding at cytoplasmic sites, is red blood cell < axolemma approximately rat alpha(1)-transfected HeLa cells < small intestine < kidney < heart. In addition, we have carried out an extensive analysis of the kinetics of K(+) binding and occlusion to the cytoplasmic cation binding site and find that, for most tissues, there is a relationship between the rate of K(+) binding/occlusion and the apparent affinity for K(+) as a competitive inhibitor of Na(+) activation, the order for both parameters being heart >/= kidney > small intestine approximately rat alpha(1)-transfected HeLa cells. The notion that modulations in cytoplasmic K(+)/Na(+) antagonism are a potential mode of pump regulation is underscored by evidence of its reversibility. Thus the relatively high K(+)/Na(+) antagonism characteristic of kidney pumps was reduced when rat kidney microsomal membranes were fused into the dog red blood cell.

Human coronary arteriolar dilation to bradykinin depends on membrane hyperpolarization: contribution of nitric oxide and Ca2+-activated K+ channels

BACKGROUND

K+ channel activation in vascular smooth muscle cells (VSMCs) plays a key role in regulating vascular tone. It has been proposed that endothelium-derived hyperpolarizing factor (EDHF) contributes to microvascular dilation more than nitric oxide (NO) does. Whether hyperpolarization is important for coronary arteriolar dilation in humans is not known. Bradykinin (BK), an endogenous vasoactive substance, is released from ischemic myocardium and regulates coronary resistance. Therefore, we tested the effects of inhibiting NO synthase, cyclooxygenase, and K+ channels on the changes in diameter and membrane potential (Em) in response to BK in isolated human coronary microvessels.

METHODS AND RESULTS

Arterioles (97+/-4 micrometers; n=120) dissected from human right atrial appendages (n=78) were cannulated at a distending pressure of 60 mm Hg and zero flow. Changes in vessel diameter (video microscopy) and VSMC Em (glass microelectrodes) were measured simultaneously. In vessels constricted and depolarized (Em; -50+/-3 to -28+/-2 mV) with endothelin-1 (ET), dilation to BK was associated with greater membrane hyperpolarization (-48+/-3 mV at 10(-6) mol/L) than dilation to sodium nitroprusside (SNP) (-34+/-2 mV at 10(-4) mol/L) for similar degrees of dilation. Treatment with Nomega-nitro-L-arginine methyl ester (L-NAME; 10(-4) mol/L), an NO synthase inhibitor, partially decreased dilation to BK (maximum dilation 61+/-10% versus control 92+/-4%; P<0.05). Charybdotoxin (CTX; 10(-8) mol/L), a large-conductance Ca2+-activated K+ channel blocker, or apamin (10(-7) mol/L), a small-conductance Ca2+-activated K+ channel blocker, inhibited both dilation (CTX 22+/-6% and apamin 45+/-10% versus control 69+/-6%; P<0.05) and membrane hyperpolarization (CTX -31+/-2 mV and apamin -37+/-2 mV versus control -44+/-2 mV; P<0.05) to BK, whereas glibenclamide (10(-6) mol/L), an ATP-sensitive K+ channel blocker, was without effect.

CONCLUSIONS

Vasodilation of human coronary arterioles to BK is largely dependent on membrane hyperpolarization by Ca2+-activated K+ channel activation, with apparently less of a role for endothelium-derived NO. This suggests a role for K+ channel activation in regulating human coronary arteriolar tone.

Adenosine and ADP prevent apoptosis in cultured rat cerebellar granule cells

Cerebellar granule cells (CGCs) explanted in vitro undergo death via apoptosis when the concentration of potassium is shifted from 25 mM to 5 mM. We report that adenosine and ADP, which act as neurotransmitters and neuromodulators in the brain, exert in cultured cerebellar granule cells a specific and marked antiapoptotic action with half-maximal effect in the 10-100 microM range. The action of adenosine is partly inhibited by the A1AR antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and is mimicked by the A1AR agonist 2-chloro-N6-cyclopentyladenosine (CCPA), while ADP effect, that is completely blocked by the P2x, P2y receptors noncompetitive antagonist suramine, is restored in the presence of the selective P2x purinoceptors agonist beta, gamma-methylene-L-ATP. These findings demonstrate that adenosine and ADP markedly inhibit the program of cell death in cerebellar granule cells and suggest that such an action is mediated via interaction with, respectively, A1 and P2x receptors.

The role of urinary potassium in the pathogenesis and diagnosis of interstitial cystitis

PURPOSE

We determined whether intravesical potassium absorption in normal bladders correlates with increased sensory urgency, and corroborated the hypothesis that mucus is important in the regulation of epithelial permeability. We compared sensory nerve provocative ability of sodium versus potassium, and determined whether intravesical potassium sensitivity discriminates patients with interstitial cystitis from normal subjects and those with other sensory disorders of the bladder.

MATERIALS AND METHODS

A total of 231 patients with interstitial cystitis and 41 normal subjects underwent intravesical challenge with 40 ml. water and then 40 ml. of 40 mEq./100 ml. potassium chloride. Subjective responses of urgency or pain stimulation were recorded on a scale of 0 to 5. In 19 normal subjects potassium absorption was measured at baseline, after injury of the bladder mucus with protamine, after heparin treatment to reverse mucus damage and then for a final time. These subjects simultaneously recorded the symptoms of sensory urgency and pain at baseline, after protamine and after heparin. Another group of normal volunteers underwent a challenge with sodium versus potassium to determine which cation was more provocative. Patients with bladder outlet obstruction secondary to benign prostatic hyperplasia (BPH), detrusor instability, and acute and chronic urinary tract infection but no current infection were also evaluated for potassium sensitivity.

RESULTS

Neither normal subjects nor patients with interstitial cystitis reacted to water administered intravesically. There was marked sensitivity to intravesical potassium in 75% of patients with interstitial cystitis versus 4% of controls (p <0.01). Only 1 patient with BPH responded to potassium and none of the 5 with chronic urinary tract infection responded. All 4 patients (100%) with a current acute urinary tract infection reacted positively to the potassium challenge. Of 16 patients with detrusor instability 25% responded. Normal subjects had minimal sensitivity to potassium before (11%) and markedly increased sensitivity after (79%) protamine treatment, and these symptoms were reversed by heparin in 42%. Potassium absorption directly correlated with symptoms (0.4, 3.0 and 1.3 mEq. before and after protamine, and after heparin reversal, respectively). In regard to sodium versus potassium provocation, potassium was far more provocative for causing urgency after protamine (10 versus 90%). Neither group underwent provocation before protamine.

CONCLUSIONS

Chronic diffusion of urinary potassium into the bladder interstitium may induce sensory symptoms, damage tissue and be a major toxic factor in the pathogenesis of interstitial cystitis. Intravesical potassium sensitivity is a reliable method for detecting abnormal epithelial permeability. It discriminates between patients with interstitial cystitis and normal subjects with intact epithelial function, and it is a useful diagnostic test for interstitial cystitis. Potassium sensitivity correlates with increased potassium absorption in normal subjects, and potassium is far more provocative than sodium. Potassium sensitivity is also present in acute urinary tract infection and occasionally detrusor instability but not in BPH or chronic urinary tract infections.

Cadmium uptake from apical membrane of LLC-PK1 cells via inorganic anion exchanger

Effects of Na+, Cl-, OH- and HCO3-, and an inorganic anion exchange inhibitor (HCO3-/Cl-), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, on Cd uptake from the apical membrane of LLC-PK1 cells were investigated to elucidate the mechanism of Cd uptake by these cells. Furthermore, the initial uptake of Cd incubated at different temperatures was analyzed by using the Arrhenius plot to test if Cd is taken up by the cells via the carrier-mediated process. The cells were incubated with 1 microM CdCl2 for 30 min. at 37 degrees in phosphate buffer containing NaCl at pH 5.5 or 7.4. Cd accumulation by the cells at pH 7.4 was about 5 times higher than at pH 5.5. Replacement of NaCl in the phosphate buffer with KCl or mannitol decreased the Cd accumulation at pH 7.4 about 80%, but had no effect at pH 5.5. The addition of 2 mM NaHCO3 to the pH 7.4 buffer containing NaCl significantly increased the Cd accumulation, and pretreatment of the cells with the inorganic anion exchange inhibitor abolished this effect of NaHCO3 on Cd accumulation. The cells were incubated for 10 min. at different temperatures with 1 microM CdCl2 in the phosphate buffer containing NaCl at pH 7.4 in the presence or absence of 2 mM NaHCO3 or at pH 5.5 in the absence of NaHCO3. In all cases, the Arrhenius plots of Cd accumulation were nonlinear. The breakpoint was observed at about 30 degrees in the Cd accumulation at pH 7.4 in the presence of NaHCO3, suggesting the involvement of a carrier-mediated process. This breakpoint was not as clear in the Cd accumulation at pH 7.4 in the absence of NaHCO3 and not observed at all at pH 5.5. These findings suggested that Cd is partially taken up from the apical membrane of LLC-PK1 cells via the inorganic anion exchanger and the uptake of Cd is more efficient at alkaline pH and in the presence of Na+, Cl- and HCO3-.

[Functional test with potassium chloride following long-term space mission]

To look into the potassiuretic function of kidneys in 11 cosmonauts on the second day post recovery after six-month MIR missions, functional testing with potassium chloride was performed. The following standard procedure was used before and after the missions: during morning hours fasting test-subjects consumed a 10% solution of potassium chloride in the amount of 0.55 ml/kg or 0.75 mmol of potassium per a kilogram of body mass with some additional liquid in the amount of 10 ml/kg of body mass. Later on, urine was collected for four hours. Administration of the potassium loading test after missions did not reveal any significant group-average changes in potassium excretion as compared with pre-flight levels; meanwhile, calcium excretion was increased. Reduced blood concentrations of potassium were determined in each of the cosmonauts immediately after landing. The main contributor to retaining of the renal potassiuretic function after prolonged missions appears to be the effective inflight physical countermeasures against the musculoskeletal deconditioning of the human body.

[Comparison of extra renal potassium management in hypertensive, diabetic and normal subjects]

BACKGROUND

Sodium and potassium ions are involved in the regulation of blood pressure and the genesis of hypertension.

AIM

To assess internal potassium balance, as a measure of sodium pump activity, in subjects with essential hypertension and diabetic patients.

PATIENTS AND METHODS

Eleven hypertensive subjects, 5 non-insulin-dependent diabetics and 16 age matched controls were studied. An acute oral load of 0.8 mEq/Kg body weight of KCl was administered and blood samples were drawn every 30 min thereafter, until 120 min, to measure plasma K+ levels. Urinary K+ excretion during this period was also measured. In eight hypertensive patients, the test was repeated after two week of supplementation with 60 mEq/day of KCl. The maximal increase in plasma potassium levels and the time required to achieve the maximum concentration was recorded.

RESULTS

All patients had normal serum creatinine levels. Mean fasting blood glucose of diabetic patients was 133 +/- 15.1 mg/dl. No difference between patients and controls in maximal increase plasma potassium increase, was observed. In hypertensive patients the lapse to achieve the maximal potassium concentration was longer than in controls. After the period of potassium supplementation in hypertensive patients, there was a significant increase in basal plasma K+ levels and the temporal pattern of plasma potassium increase was similar to that of controls. Between 63 and 68% of retained K+ load was translocated to the intracellular space at 120 min in all study groups.

CONCLUSIONS

Internal potassium balance is not significantly altered in subjects with essential hypertension or in non-insulin-dependent diabetics.

Do HbSS erythrocytes lose KCl in physiological conditions?

KCl cotransporter activity in sickle (HbSS) red blood cells (RBCs) was measured in cells suspended in 'simple' physiological saline, saline augmented with inorganic salts, and autologous plasma. Our results showed that the transporter was only functioning at 20% of the level of cells in saline when cells were resuspended in autologous plasma. Kinetic analysis of the data showed that plasma decreased both Vmax and Km for K+ of the transporter. The plasma factor(s) responsible was heat-stable and dialysable (i.e. size < 10 kD). Adding magnesium, calcium, inorganic phosphate or bicarbonate to 'simple' saline to mimic the effect of plasma revealed that Mg2+ and Ca2+ had no significant effect at physiological concentrations. Pi was not effective at 1.1 mM, but did inhibit significantly (42+/-2%) at 5.6 mM. HCO3- had a major inhibitory effect on K+ influx when added to saline, and was identified as the principal candidate for the plasma effect. We suggest bicarbonate may play a significant role in modifying KCl cotransport, and hence HbSS cell volume in vivo. It acts by altering the set point of the transporter via the signalling systems involved in its regulation.

Vascular chemical sulfhydryl alkylation in vitro: alterations in intracellular calcium and cAMP and cGMP metabolism

This study examined the effect of N-ethylmaleimide (NEM, 10(-7) M) on agonist-induced contraction and the relaxation following drug-washout, of vascular smooth muscle (VSM) segments derived from hypertensive rabbits. Mean blood pressure increase was produced either by renal constriction plus contralateral nephrectomy, or by cadmium acetate ingestion. Freely-ionized calcium (45Ca)flux, cyclic 3':5'-guanosine monophosphate (cGMP), and cyclic 3':5' adenosine monophosphate (cAMP), were analyzed. NEM was used as a stereoselective probe to clarify the role of sulfhydryl (SH) groups in hypertension. Contractile response to norepinephrine (NE, 5.9 x 10(-7) M), angiotensin II (AT, 9.8 x 10(-8) M), and potassium chloride (KCl, 2.2 x 10(-2) M) were significantly depressed in hypertensive tissue. Exposure to NEM, before agonist challenge, caused an even greater depression in contractile response. As for the normotensive group, an inhibition of relaxation occurred when NEM was added after the development of a maximal contractile response to NE, AT or KCl. Changes in contractile ability and in relaxation were attributed to specific alterations in calcium distribution. These alterations were examined by 45Ca washout components and were related to cAMP and cGMP metabolism. These results suggest a regulatory role of SH groups in contraction and relaxation and a modification of this role in hypertension.

Changes in the permselectivity of human teeth during caries attack

Previous studies have shown that enamel permselectivity can influence fluid composition within caries lesions during de- and remineralization. The permselectivity of human enamel, cementum, and dentin sections was examined, in a microwell model, by measurement of the membrane potential developed by KCl diffusion while the sections were immersed in solutions simulating resting (pH = 5.6) and cariogenic plaque fluid (pH = 4.8). In a second experiment, the effects of charged compounds (phytate and Zonyl-FSC) on the tooth permselectivity were examined. The average membrane potentials (+/- SD) in "resting plaque" solution were: sound enamel, 18.9 +/- 3.2 mV, n = 66; dentin, 0.9 +/- 9.2 mV, n = 59; and cementum, -0.8 +/- 8.2 mV, n = 42, with a positive sing indicating cation selectivity. The average membrane potentials became more negative in "cariogenic plaque" solution for all types of sections: sound enamel, 5.2 +/- 2.1 mV, n = 46; dentin, -8.1 +/- 7.4 mV, n = 45; and cementum, -14.3 +/- 8.0 mV, n = 34. In lesion enamel sections, the membrane potential was reduced from the non-lesion wells in both types of test solutions, while phytate treatment caused an increase of approximately 10 mV in potential (increased cation selectivity) in every enamel well in either "resting" or "cariogenic" solution. Treatment of enamel sections with Zonyl-FSC caused the membrane potential to become more negative in both test solutions, with many of the wells showing anion selectivity in the cariogenic "plaque-like" solution. However, the changes in enamel membrane potentials induced by Zonyl-FSC slowly increased toward the initial values after treatment, while the effects of the phytate pre-treatment persisted. Most dentin sections treated with phytate also showed an increase in potential after phytate treatment; however, Zonyl-FSC seemed to have little effect on the membrane potential of dentin. The results of this study suggest that modification of tooth permselectivity by surface-active agents may be a viable method of decreasing the rate of caries progression.

What is the better formulation of microencapsulated potassium chloride?

A single blind cross-over study was performed comparing a new microencapsulated potassium chloride tablet (MET) with two reference formulations of oral potassium, namely potassium chloride solution (PS), and microencapsulated potassium chloride capsules (MEC), in 18 normal healthy volunteers. The potassium chloride induced change in gastric potential difference (PD) of the mucosa was the main criterion of comparison and was assessed by the area above curve (AAC), the total duration of the effect (TDE), the maximal variation of PD (delta MAX), and the aggression index (AI). The results showed that all three formulations induced a fall in PD; the delta MAX and AAC were significantly greater for PS indicating a higher aggressive effect of the solution; MET had significantly less aggressive effect than MEC when assessed by all parameters.

Efflux of taurine from renal brush border membrane vesicles: is it adaptively regulated?

The uptake of the beta-amino acid taurine by rat renal brush border membrane vesicles (BBMV) adapts to changes in dietary sulfur amino acid intake. Initial rate Vmax "upregulates" after ingestion of a low methionine and taurine diet (LTD) and "downregulates" after a high taurine diet (HTD). This is reflected in vivo by hypotaurinuria after a LTD (90% reduction in excretion) and an 18-fold increase in urine taurine after a HTD. This study was performed to determine whether taurine efflux from BBMV is adaptively regulated by external taurine concentration or by diet. Vesicles were preloaded with varying concentrations of radiolabelled and unlabelled taurine and a 150 mM concentration of various salts. Efflux conditions were: taurine and 150 mM salt inside and 150 mM salt outside. The efflux of five concentrations of taurine (10-500 microM) was linear over 6 min, reached equilibrium by 21 min, and was dependent upon intravesicular taurine content. The kinetic characteristics of efflux (E) were significantly different from influx (I): Km = 109.8 +/- 5.8 (E) versus 23.6 +/- 4.2 (I), P < 0.001 [time of linearity = 360 s (E) vs. 20 s (I)]. Efflux of taurine was dependent on the presence of both sodium and chloride in the system, but neither external taurine content (0.100 microM, 1,000 microM) nor external beta-alanine altered initial efflux. Feeding rats a normal diet, LTD, or fasting altered taurine uptake but not efflux. Efflux does not appear to play a role in the adaptive regulation of taurine transport found in all mammalian species.

Salivary clearance from different regions of the mouth in children

The aim of this study was to evaluate the rates of salivary clearance at seven different locations in children. The diffusant was 1 mol/l KCl in a 1.0% agarose matrix, placed in small acrylic devices which could be fastened to the teeth with dental floss. The diffusion chambers were taken from the mouth at selected time intervals and the gels transferred quantitatively to flasks containing 400 ml of 100 ppm NaCl. The fluid was agitated intermittently for 1 h and analyzed for potassium by atomic absorption spectrophotometry. For 12 subjects (5 years of age), the clearance halftimes (the time for the initial potassium concentration to decrease by half) were lowest in the lower anterior lingual regions and were highest in the upper anterior buccal regions. When the salivary flow was stimulated, the clearance halftimes for the lower and upper anterior buccal sites in the 6 subjects without spaces between their anterior teeth were significantly higher than in the 6 subjects with spaces. The results show that the clearance halftime is longest for the upper anterior buccal site which is the site most prone to nursing bottle caries in the deciduous dentition.

Permselectivity of sound and carious human dental enamel as measured by membrane potential

A microwell technique was used for determination of the permselectivities of sound and carious enamel in the same slice of tooth. The permselectivity determination was accomplished by drilling microwells in the enamel and filling them with a simulated plaque fluid containing lactate, carbonate, and inorganic ions at concentrations similar to those in resting plaque fluid, but with different concentrations of KCl. The electrical potentials developed across the enamel membrane were measured with microreference electrodes placed in the wells or in the solution outside the tooth. The results showed that the membrane potential was a function of the composition of the solutions separated by the enamel membrane and was independent of the composition of the solutions in the adjacent wells. The enamel was found to be cation-permselective, and sound enamel was more permselective than carious enamel. The flux rate of K+ was estimated from the change in the K+ concentration of the well solution as a function of time. The flux rate and the membrane potential data were used in the Nernst-Planck Flux Equation for calculation of the diffusion coefficient of K+ through enamel. The results indicate that the permselectivity of enamel can greatly influence the diffusion of ions through enamel membranes.

Formulation, bioavailability, and pharmacokinetics of sustained-release potassium chloride tablets

The release of potassium chloride incorporated into hydrogenated vegetable oil and hydroxypropyl methylcellulose matrix tablets was studied in vitro. The formulations containing 20% hydrogenated vegetable oil and hydroxypropyl methylcellulose showed a sustained-release profile comparable to that of a standard commercially available sustained-release preparation, containing 8 mEq potassium chloride embedded in a wax material. The formulated and standard sustained-release potassium chloride tablets were compared to a conventional enteric-coated potassium chloride tablet in 10 healthy subjects. Mean recoveries in 24-hr urine potassium levels from four dosage forms (after subtracting normal urine potassium excretion levels) were 76 +/- 32% from hydroxypropyl methylcellulose, 95 +/- 22% from hydrogenated vegetable oil-incorporated matrix tablets, 91 +/- 29% from commercially available sustained-release tablets, and 97 +/- 13% from enteric-coated tablets. There was no significant difference (P greater than 0.05) in the time to reach maximum excretion rates among the three sustained-release tablets. No significant adverse effect was experienced with any of the preparations.

A single blind normal volunteer bioavailability study of a new microencapsulated potassium chloride tablet compared with two reference potassium formulations

A single blind placebo controlled, cross-over study comparing a new microencapsulated potassium chloride tablet (MET) with two reference formulations of oral potassium, potassium chloride solution (PS) and potassium chloride wax-matrix tablets (WMT), was performed in 12 normal healthy volunteers. Urinary potassium excretion was the main criterion of comparison. Results showed that all three formulations have excellent bioavailability. This indicates that potassium absorption in the stomach is similar to that in more distant portions of the gut. The slow-release characteristics of both MET and WMT were confirmed. Clinical and pharmacological tolerance was excellent and no side-effects were reported with any of the potassium formulations studied.

[Potassium distribution in rat tissues in relation to its concentration in the blood]

The dynamics of distribution of potassium and sodium among the blood plasma and the tissues (muscle and liver) was studied in Wistar rats at an artificial increase of the potassium content in the blood. After administration of 1.25% solution of potassium chloride into the stomach (5 ml/100 g), into the liver portal vein (0.5 ml/100 g), and into femoral vein (0.1 ml/min during 45 min), the changes of potassium and sodium contents were opposite in the blood plasma and in the tissues under study. The maximal shift of these ions concentration in the plasma and tissues occurs sooner after administration of potassium directly into the blood. In continuous administration of the solution the potassium concentration reaches 10.8 mM/l in the blood plasma and returns to normal values within 2 hrs after cessation of the administration. Therefore, the redistribution of potassium between extra- and intracellular fluid plays a major role in restoration of the potassium homeostasis.

Stimulants of ileal salt transport in neuroendocrine system of the desert locust

Proteinaceous factors from the corpora cardiaca (CC) and ventral ganglia (VG) stimulate KCl transport across voltage-clamped preparations of locust ilea in a dose-dependent manner. These factors may act via cAMP as the second messenger because this cyclic nucleotide and agents which increase its cellular level all mimic the stimulatory effects of CC and VG extracts. The CC and VG factors are apparently different compounds because they differ in the time course of ileal short-circuit current (Isc) initiated, in heat stability, and in extraction properties. Because saline extracts of the CC have similar effects on both ileal and rectal segments of locust hindgut, the ileal stimulant from the CC may be the chloride transport-stimulating hormone, described by Phillips et al. (Canad. J. Zool. 58, 1851-1860, 1980) which acts to stimulate rectal Isc.

What happens to tablets and capsules in the stomach: endoscopic comparison of disintegration and dispersion characteristics of two microencapsulated potassium formulations

Previously we investigated gastric emptying and distribution of a capsule formulation of microencapsulated KCl and found the drug was usually present in clumps of KCl crystals held in place by gastric mucus. We therefore investigated whether a tablet formulation of microencapsulated KCl would have improved dispersion. We characterized the intragastric disintegration of capsules and tablets of microencapsulated KCl in 12 subjects. The capsule formulation floated in the gastric pool; one end would adhere to the gastric mucosa and the motion of the tethered capsule would pull the end of the capsule off. The KCl crystals would then be deposited in a mass. In contrast, the tablet formulation sank to the anatomically most dependent portion of the stomach. The tablet rapidly became soft and fragile but, if allowed to remain in one place and minimally disturbed, required a median of 12 min to lose its shape. If allowed to reach the gastric antrum, the tablet was quickly ground by the antro-pyloric pump and widely dispersed. Once liberated in the stomach, the microencapsulated KCl crystals were bound into a more-or-less cohesive mass. The differences between KCl formulations, once the crystals were released, was minimal although the larger crystals from the tablet formulation appeared less adherent and cohesive; they dispersed more in a reticulated pattern when the stomach was distended. We conclude that formulation of a drug in a microencapsulated multiple-unit dosage form does not guarantee wide dispersion nor absence of high local concentration of drug.

Carrier-mediated Cl- transport in cultured mouse oligodendrocytes

We studied the steady state and the regulation of intracellular Cl- activity (aCl-i) and the mechanisms of KCl uptake in cultured oligodendrocytes from mouse spinal cord using Cl(-)-selective microelectrodes. The majority of oligodendrocytes actively accumulated Cl- above passive distribution (2-3 mM), few cells showed a passive Cl- distribution. To identify the carriers mediating Cl- uptake, oligodendrocytes were maintained in a solution with low extracellular Cl- concentration ([Cl-]o) which resulted in a rapid decrease in aCl-i. The recovery of aCl-i above its passive distribution in normal [Cl-]o was blocked in the absence of Na+ or in the presence of furosemide and of bumetanide, which has been reported to inhibit Na+/K+/Cl- cotransport. We therefore conclude that Cl- uptake is primarily due to the activity of a Na+K+/Cl- transport system. Cl- uptake above passive distribution was not affected in HCO3(-)-free solution or in the presence of SITS and DIDS, indicating that Cl-/HCO3- exchange is not involved in Cl- uptake by oligodendrocytes. Elevation of [K+]o induced an increase in aCl-i and, as shown earlier, intracellular K+ activity. This K+-induced Cl- uptake was not blocked by bumetanide, furosemide, SITS, or DIDS, suggesting that under conditions of raised [K+]o the combined uptake of K+ and Cl- is not mediated by a carrier, but can be explained by the entry through channels driven by Donnan forces.

Villous sodium gradient associated with volume absorption in the feline intestine: an electron-microprobe study on freeze-dried tissue

Water transport in biological tissue is driven by local osmotic gradients created by accumulation of actively transported ions in tissue compartments. To localize and measure such gradients, jejunal segments from the small intestine of anaesthetized cats were perfused with modified isotonic Krebs-Henseleit electrolyte solution, and net fluid transport was measured with a volumetric technique. The segments were then rapidly frozen, freeze-dried, and prepared for X-ray micro-analysis of elemental content. Whenever the lumen perfusate contained sodium, the apical third of the villus was found to have a sodium gradient rising to a tip concentration more than twice that at the base of the villus. This sodium gradient was associated with a chloride gradient and fluid absorption. No similar potassium gradient was found. When choline replaced sodium in the intestinal lumen, no gradient of sodium chloride was found and no net fluid absorption occurred. Absorption of fluid was thus apparently coupled to absorption of sodium through creation of a local osmotic gradient in the tip of the intestinal villus.

Parathyroid hormone interferes with extrarenal disposition of potassium in chronic renal failure

Available data suggest that the permeability of cellular membranes to potassium is affected by cytosolic calcium. Parathyroid hormone (PTH) has a calcium ionophoric property; it enhances calcium entry into many cells and it increases calcium content in a variety of tissues. Therefore, it is possible that clinical states with excess PTH may affect potassium homeostasis. The present study examined the effect of secondary hyperparathyroidism of chronic renal failure (CFR) on extrarenal potassium disposition of intravenous KCl load in rats with CRF. Experiments were performed after 21-26 days of CRF produced by 7/8 nephrectomy in rats with intact parathyroid glands (CRF control), in normocalcemic parathyroidectomized CRF animals (CFR-PTX) and in adrenalectomized CRF rats (CRF-ADX) maintained with DOCA. The effects of treatment with calcium channel blocker, verapamil, and of PTH administration were also examined. The baseline plasma concentrations of potassium in CRF-PTX rats and in CRF control animals treated with verapamil were significantly (p less than 0.01) lower than those with CRF control and CRF-ADX rats. At the end of 90 min of KCl infusion, the plasma concentrations of potassium as well as the changes from baseline were significantly (p less than 0.01) higher in CRF animals with secondary hyperparathyroidism (CRF control and CRF-ADX) and in those treated with PTH (CRF control with PTH and CRF-PTX with PTH) than in those without secondary hyperparathyroidism CRF-PTX and in those with secondary hyperparathyroidism but treated with verapamil (CRF control with verapamil and CRF-ADX with verapamil).(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of absorption of inorganic mercury from rat small intestine. II. Composite effects of pH and halide ions on transport of mercuric chloride into isolated brush border membrane vesicles in rats

Composite effects of pH and halide ions on the transport of HgCl2 into brush border membrane vesicles (BBMV) were investigated in rats. BBMV were incubated for 10 min. in buffer solution at different pH containing 10(-4) M HgCl2. The increase in pH increased the uptake of Hg by BBMV as a result of the increase in transport of Hg into intravesicular space and decrease in binding of Hg to BBMV. The isotonic displacement of NaCl in the buffer solution by LiCl or KCl did not change the uptake of Hg at each pH. The displacement of NaCl by mannitol increased the uptake of Hg at each pH, while the displacement by NaBr or NaI decreased the uptake and diminished the increasing effect of pH on the uptake of Hg. These changes in uptake of Hg due to the displacement were mainly ascribed to the changes in transport of Hg. These results suggest that the increase in pH mainly increases the transport of HgCl2 as a result of the conversion to hydroxide forms of Hg such as Hg(OH)Cl and Hg(OH)2, and Cl- Br- and I- act as the competing ions with OH- and decrease the transport of Hg.

Bioavailability of potassium from three dosage forms: suspension, capsule, and solution

A crossover study was performed in 28, healthy, male volunteers to determine the bioavailability of potassium from a suspension containing microencapsulated potassium chloride compared with that from a marketed microencapsulated potassium chloride capsule and a marketed potassium chloride solution. The 20-day study consisted of four, five-day periods. In three of the periods, a single, 40-mEq dose of one of the potassium formulations was administered; no drug treatment was given in the remaining period so that the amount of potassium contributed by dietary sources could be determined. Meals were served that provided controlled amounts of potassium and sodium. Bioavailability was represented by cumulative amount of K+ excreted in urine 24 and 48 hours after drug administration. The rate of absorption was calculated from excretion rates during each of the intervals of urine collection on Days 4. The pattern of excretion exhibited by the solution indicated rapid absorption and elimination. The potassium from the suspension and the capsules was excreted more slowly and over a longer period, indicating that the potassium content from these formulations was not being dumped. No statistically significant differences between the suspension and the capsules were found. The extent of absorption of K+ was similar from all three products, and the potassium from the suspension was found to be fully bioavailable when compared with the liquid and the capsule.

Lingual epithelium of spontaneously hypertensive rats has decreased short-circuit current in response to NaCl

Alterations in ion transport associated with hypertension have been found in a variety of organs. We used a modified Ussing chamber to compare the NaCl dependence of the short-circuit current across the dorsal lingual epithelium in vitro from spontaneously hypertensive rats (SHR) with that from Wistar-Kyoto rats (WKY). The short-circuit current in response to mucosal NaCl was less in SHR than in WKY at hyperosmotic concentrations (above 0.15 M and up to 2.0 M). Since ion transport in the lingual epithelium has been found to play a role in early events of salt taste transduction, the attenuation in the short-circuit current in hypertensive animals may be a factor in the enhanced salt preference of SHR compared with WKY.

Bioavailability and pharmacokinetics of a new sustained-release potassium chloride tablet

The bioavailability of a new sustained-release potassium chloride (KCl) tablet, designed for once-a-day dosing, was compared to a KCl elixir using urinary excretion data. The study utilized 25 male volunteers dosed in a crossover design in a dietary/activity-controlled environment. The regimens consisted of a total of 80 mEq of potassium in three equally divided doses of elixir every 6 hr and a single 80-mEq dose using four 20-mEq sustained-release (SR) tablets. The mean time to maximum rate of potassium urinary excretion was 2.2 hr for the first elixir dose and 5.5 hr after the SR tablet (P less than 0.01), thereby supporting the prolonged-release properties of this formulation. After correction for baseline urinary potassium excretion, the mean total 24-hr urinary potassium excretion was 42.18 mEq for the elixir and 40.41 mEq for the SR tablet. The results indicate that the absorption pattern from the SR tablet is equal to three doses of KCl elixir dosed 6 hr apart.