Inhibition of K+ secretion in the distal nephron in nephrotic syndrome: possible role of albuminuria.

Nephrotic syndrome features massive proteinuria and retention of sodium which promotes ascite formation. In the puromycin aminonucleoside-induced rat model of nephrotic syndrome, sodium retention originates from the collecting duct where it generates a driving force for potassium secretion. However, there is no evidence for urinary potassium loss or hypokalaemia in the nephrotic syndrome. We therefore investigated the mechanism preventing urinary potassium loss in the nephrotic rats and, for comparison, in hypovolaemic rats, another model displaying increased sodium reabsorption in collecting ducts. We found that sodium retention is not associated with urinary loss of potassium in either nephrotic or hypovolaemic rats, but that different mechanisms account for potassium conservation in the two models. Collecting ducts from hypovolaemic rats displayed high expression of the potassium-secreting channel ROMK but no driving force for potassium secretion owing to low luminal sodium availability. In contrast, collecting ducts from nephrotic rats displayed a high driving force for potassium secretion but no ROMK. Down-regulation of ROMK in nephrotic rats probably stems from phosphorylation of ERK arising from the presence of proteins in the luminal fluid. In addition, nephrotic rats displayed a blunted capacity to excrete potassium when fed a potassium-rich diet, and developed hyperkalaemia. As nephrotic patients were found to display plasma potassium levels in the normal to high range, we would recommend not only a low sodium diet but also a controlled potassium diet for patients with nephrotic syndrome.

Activation of the basolateral membrane Cl- conductance essential for electrogenic K+ secretion suppresses electrogenic Cl- secretion.

Adrenaline activates transient Cl(-) secretion and sustained K(+) secretion across isolated distal colonic mucosa of guinea-pigs. The Ca(2+)-activated Cl(-) channel inhibitor CaCCinh-A01 (30 µm) significantly reduced electrogenic K(+) secretion, detected as short-circuit current (I(sc)). This inhibition supported the cell model for K(+) secretion in which basolateral membrane Cl(-) channels provide an exit pathway for Cl(-) entering the cell via Na(+)-K(+)-2Cl(-) cotransporters. CaCCinh-A01 inhibited both I(sc) and transepithelial conductance in a concentration-dependent manner (IC(50) = 6.3 µm). Another Cl(-) channel inhibitor, GlyH-101, also reduced sustained adrenaline-activated I(sc) (IC(50) = 9.4 µm). Adrenaline activated whole-cell Cl(-) current in isolated intact colonic crypts, confirmed by ion substitution. This adrenaline-activated whole-cell Cl(-) current was also inhibited by CaCCinh-A01 or GlyH-101. In contrast to K(+) secretion, CaCCinh-A01 augmented the electrogenic Cl(-) secretion activated by adrenaline as well as that activated by prostaglandin E(2). Synergistic Cl(-) secretion activated by cholinergic/prostaglandin E(2) stimulation was insensitive to CaCCinh-A01. Colonic expression of the Ca(2+)-activated Cl(-) channel protein Tmem16A was supported by RT-PCR detection of Tmem16A mRNA, by immunoblot with a Tmem16A antibody, and by detection of immunofluorescence in lateral membranes of epithelial cells. Alternative splices of Tmem16A were detected for exons that are involved in channel activation. Inhibition of K(+) secretion and augmentation of Cl(-) secretion by CaCCinh-A01 support a common colonic cell model for these two ion secretory processes, such that activation of basolateral membrane Cl(-) channels contributes to the production of electrogenic K(+) secretion and limits the rate of Cl(-) secretion. Maximal physiological Cl(-) secretion occurs only for synergistic activation mechanisms that close these basolateral membrane Cl(-) channels.

Leu27 insulin-like growth factor-II, an insulin-like growth factor-II analog, attenuates depolarization-evoked GABA release from adult rat hippocampal and cortical slices.

Accumulated evidence suggests that the single transmembrane domain insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M6P or IGF-II receptor) plays an important role in the intracellular trafficking of lysosomal enzymes and endocytosis-mediated degradation of insulin like growth factor (IGF-II). However, the role of this receptor in signal transduction following IGF-II binding remains controversial. In the present study, we revealed that Leu(27)IGF-II, an analog which binds preferentially to the IGF-II receptor, can attenuate K(+)-as well as veratridine-evoked GABA release from the adult rat hippocampal formation. Tetrodotoxin failed to alter the effects of Leu(27)IGF-II on GABA release, thus suggesting the lack of involvement of voltage-dependent Na(+) channels. Interestingly, the effect is found to be sensitive to pertussis toxin (PTX), indicating the possible involvement of a Gi/o protein-dependent pathway in mediating the release of GABA from the hippocampal slices. Additionally, Leu(27)IGF-II was found to attenuate GABA release from frontal cortex but not from striatum. These results, together with the evidence that IGF-II receptors are localized on GABAergic neurons, raised the possibility that this receptor, apart from mediating intracellular trafficking, may also be involved in the regulation of endogenous GABA release by acting directly on GABAergic terminals.

The slow Ca2+ -dependent K+ -current facilitates synchronization of hyperexcitable pyramidal neurons.

Studies on in vivo and in vitro epilepsy models have shown that progression and maintenance of epileptiform activity can be affected by the slow Ca(2+)-dependent K(+) current (I(sAHP)). This study aimed to investigate the influence of the I(sAHP) on population activity and single cell activity during the transition from the interictal- to the ictal-like phase of an epileptiform field potential induced by Cs(+). Extracellular and intracellular recordings were performed in area CA1 on 400 microm thick hippocampal slices from adult male Wistar rats. During maintained exposure to Cs(+), the transition between the two phases underwent a slow, time-dependent change, where synchronized population activity gradually disappeared and a plateau-like prolongation of the interictal-like phase emerged. In parallel, the size of the ictal-like phase increased. These effects could be ascribed to a gradual block of the I(sAHP) and were mimicked by the I(sAHP) antagonists carbacholine (2 microM), isoproterenol (4 microM) and Ba(2+) (0.2 mM). Cessation of population activity generally occurred without a concomitant decrease in firing rate of single CA1 pyramidal neurons, but was accompanied by the disappearance of hyperpolarizing prepotentials, indicating a shift in the mechanism of action potential initiation. These findings suggest that the presence of the I(sAHP) increases the tendency of hyperexcitable neurons to fire in synchrony, but at the same time serves to dampen the ictal-like activity that follows the hyperexcitable state. Our data indicate that both effects can be attributed to the influence of this current on the steady-state membrane potential in the period of the transition from interictal- to ictal-like activity.

Conditional knock-out of Kir4.1 leads to glial membrane depolarization, inhibition of potassium and glutamate uptake, and enhanced short-term synaptic potentiation.

During neuronal activity, extracellular potassium concentration ([K+]out) becomes elevated and, if uncorrected, causes neuronal depolarization, hyperexcitability, and seizures. Clearance of K+ from the extracellular space, termed K+ spatial buffering, is considered to be an important function of astrocytes. Results from a number of studies suggest that maintenance of [K+]out by astrocytes is mediated by K+ uptake through the inward-rectifying Kir4.1 channels. To study the role of this channel in astrocyte physiology and neuronal excitability, we generated a conditional knock-out (cKO) of Kir4.1 directed to astrocytes via the human glial fibrillary acidic protein promoter gfa2. Kir4.1 cKO mice die prematurely and display severe ataxia and stress-induced seizures. Electrophysiological recordings revealed severe depolarization of both passive astrocytes and complex glia in Kir4.1 cKO hippocampal slices. Complex cell depolarization appears to be a direct consequence of Kir4.1 removal, whereas passive astrocyte depolarization seems to arise from an indirect developmental process. Furthermore, we observed a significant loss of complex glia, suggestive of a role for Kir4.1 in astrocyte development. Kir4.1 cKO passive astrocytes displayed a marked impairment of both K+ and glutamate uptake. Surprisingly, membrane and action potential properties of CA1 pyramidal neurons, as well as basal synaptic transmission in the CA1 stratum radiatum appeared unaffected, whereas spontaneous neuronal activity was reduced in the Kir4.1 cKO. However, high-frequency stimulation revealed greatly elevated posttetanic potentiation and short-term potentiation in Kir4.1 cKO hippocampus. Our findings implicate a role for glial Kir4.1 channel subunit in the modulation of synaptic strength.

KSper, a pH-sensitive K+ current that controls sperm membrane potential.

Mature mammalian spermatozoa are quiescent in the male reproductive tract. Upon ejaculation and during their transit through the female reproductive tract, they undergo changes that enable them to fertilize the egg. During this process of capacitation, they acquire progressive motility, develop hyperactivated motility, and are readied for the acrosome reaction. All of these processes are regulated by intracellular pH. In the female reproductive tract, the spermatozoan cytoplasm alkalinizes, which in turn activates a Ca2+-selective current (I(CatSper)) required for hyperactivated motility. Here, we show that alkalinization also has a dramatic effect on membrane potential, producing a rapid hyperpolarization. This hyperpolarization is primarily mediated by a weakly outwardly rectifying K+ current (I(KSper)) originating from the principal piece of the sperm flagellum. Alkalinization activates the pH(i)-sensitive I(KSper), setting the membrane potential to negative potentials where Ca2+ entry via I(CatSper) is maximized. I(KSper) is one of two dominant ion currents of capacitated sperm cells.

Distinct K+ conductive pathways are required for Cl- and K+ secretion across distal colonic epithelium.

Secretion of Cl(-) and K(+) in the colonic epithelium operates through a cellular mechanism requiring K(+) channels in the basolateral and apical membranes. Transepithelial current [short-circuit current (I(sc))] and conductance (G(t)) were measured for isolated distal colonic mucosa during secretory activation by epinephrine (Epi) or PGE(2) and synergistically by PGE(2) and carbachol (PGE(2) + CCh). TRAM-34 at 0.5 microM, an inhibitor of K(Ca)3.1 (IK, Kcnn4) K(+) channels (H. Wulff, M. J. Miller, W. Hänsel, S. Grissmer, M. D. Cahalan, and K. G. Chandy. Proc Natl Acad Sci USA 97: 8151-8156, 2000), did not alter secretory I(sc) or G(t) in guinea pig or rat colon. The presence of K(Ca)3.1 in the mucosa was confirmed by immunoblot and immunofluorescence detection. At 100 microM, TRAM-34 inhibited I(sc) and G(t) activated by Epi ( approximately 4%), PGE(2) ( approximately 30%) and PGE(2) + CCh ( approximately 60%). The IC(50) of 4.0 microM implicated involvement of K(+) channels other than K(Ca)3.1. The secretory responses augmented by the K(+) channel opener 1-EBIO were inhibited only at a high concentration of TRAM-34, suggesting further that K(Ca)3.1 was not involved. Sensitivity of the synergistic response (PGE(2) + CCh) to a high concentration TRAM-34 supported a requirement for multiple K(+) conductive pathways in secretion. Clofilium (100 microM), a quaternary ammonium, inhibited Cl(-) secretory I(sc) and G(t) activated by PGE(2) ( approximately 20%) but not K(+) secretion activated by Epi. Thus Cl(-) secretion activated by physiological secretagogues occurred without apparent activity of K(Ca)3.1 channels but was dependent on other types of K(+) channels sensitive to high concentrations of TRAM-34 and/or clofilium.

[A study on K469E polymorphism of ICAM1 gene and ICAM1 plasma level in patients with coronary heart disease].

OBJECTIVE: To study the linkage between K469E polymorphism of intercellular adhesion molecule 1(ICAM1) gene with ICAM1 plasma level and coronary heart disease (CHD) in Han population of China. METHODS: One hundred and sixty-four controls without CHD and 160 patients with CHD were enrolled in our study. By nested PCR with allele-specific oligonucleotide primers, all patients and controls were genotyped for the ICAM1 polymorphism. And the ICAM1 plasma level was measured by ELISA. RESULTS: In the patients with CHD, both K allele frequency and the plasma level of ICAM1 were higher than those in control (P<0.05). The individual with K allele had higher plasma level of ICAM1 than that without K allele (344.34+/-128.59 microg/L vs 303.54+/-108.74 microg/L, P=0.008). K allele enhanced the risk of CHD (P<0.01, OR=2.158, 95%CI: 1.250-3.727). There was the K allele cooperation with smoking in influencing the risk of CHD. CONCLUSION: There is the polymorphism of ICAM1 K469E gene in Han population of China, and the K allele may be a genetic factor influencing the risk of CHD.

Pharmacological modulation of lung cancer cells for potassium ion depletion.

BACKGROUND: Depletion of intracellular potassium ions (K+) is necessary for cells to shrink, induce DNA fragmentation and activate caspases, events which are features of apoptosis. MATERIALS AND METHODS: We used 86Rb+ as a K+ analogue to evaluate the possibility of pharmacologically depleting human pulmonary mesothelioma (P31) and small cell lung cancer (U1690) cells of K+, for future use in studies of apoptosis induction. RESULTS: The Na+, K+, 2CI(-)-cotransport inhibitor bumetanide transiently inhibited 86Rb+ influx, but when combined with the Na+, K+, ATPase pump inhibitor ouabain there was a marked and lasting (up to 6 h) 86Rb+ influx inhibition. Cellular K+ efflux was augmented by amphotericin B, digitonin and nigericin. Amphotericin B was an effective 86Rb+ efflux stimulator with low cytotoxicity, whereas digitonin caused cell detachment and nigericin increased LDH release in the U1690 cell line, indicating considerable toxicity of the drugs. CONCLUSION: It is possible to efficiently reduce intracellular K+ by persistent K+ influx inhibition and simultaneous K+ efflux stimulation with clinically available drugs.

Influence of naloxone on catecholamine release evoked by nicotinic receptor stimulation in the isolated rat adrenal gland.

The present study was designed to investigate the effect of naloxone, a well known opioid antagonist, on the secretion of catecholamines (CA) evoked by cholinergic stimulation and membrane-depolarization in the isolated perfused rat adrenal glands, and to establish its mechanism of action. Naloxone (10(-6) approximately 10(-5) M), perfused into an adrenal vein for 60 min, produced dose- and time-dependent inhibition of CA secretory responses evoked by ACh (5.32 x 10(-3) M), high K+ (5.6 x 10(-2) M), DMPP (10(-4) M) and McN-A-343 (10(-4) M). Naloxone itself also failed to affect the basal CA output. In adrenal glands loaded with naloxone (3 x 10(-6) M), the CA secretory responses evoked by Bay-K-8644, an activator of L-type Ca2+ channels, and cyclopiazonic acid, an inhibitor of cytoplasmic Ca(2+)-ATPase, were also inhibited. In the presence of met-enkephalin (5 x 10(-6) M), a well known opioid agonist, the CA secretory responses evoked by ACh, high K+, DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid were also significantly inhibited. Taken together, these results suggest that naloxone greatly inhibits the CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors as well as that by membrane depolarization. It seems that these inhibitory effects of naloxone does not involve opioid receptors, but might be mediated by blocking both the calcium influx into the rat adrenal medullary chromaffin cells and the uptake of Ca2+ into the cytoplasmic calcium store, which are at least partly relevant to the direct interaction with the nicotinic receptor itself.

Na+-K+ pump activation inhibits endothelium-dependent relaxation by activating the forward mode of Na+/Ca2+ exchanger in mouse aorta.

The effect of Na+-K+ pump activation on endothelium-dependent relaxation (EDR) and on intracellular Ca2+ concentration ([Ca2+]i) was examined in mouse aorta and mouse aortic endothelial cells (MAECs). The Na+-K+ pump was activated by increasing extracellular K+ concentration ([K+]o) from 6 to 12 mM. In aortic rings, the Na+ ionophore monensin evoked EDR, and this EDR was inhibited by the Na+/Ca2+ exchanger (NCX; reverse mode) inhibitor KB-R7943. Monensin-induced Na+ loading or extracellular Na+ depletion (Na+ replaced by Li+) increased [Ca2+]i in MAECs, and this increase was inhibited by KB-R7943. Na+-K+ pump activation inhibited EDR and [Ca2+]i increase (K+-induced inhibition of EDR and [Ca2+]i increase). The Na+-K+ pump inhibitor ouabain inhibited K+-induced inhibition of EDR. Monensin (>0.1 microM) and the NCX (forward and reverse mode) inhibitors 2'4'-dichlorobenzamil (>10 microM) or Ni2+ (>100 microM) inhibited K+-induced inhibition of EDR and [Ca2+]i increase. KB-R7943 did not inhibit K+-induced inhibition at up to 10 microM but did at 30 microM. In current-clamped MAECs, an increase in [K+]o from 6 to 12 mM depolarized the membrane potential, which was inhibited by ouabain, Ni2+, or KB-R7943. In aortic rings, the concentration of cGMP was significantly increased by acetylcholine and decreased on increasing [K+]o from 6 to 12 mM. This decrease in cGMP was significantly inhibited by pretreating with ouabain (100 microM), Ni2+ (300 microM), or KB-R7943 (30 microM). These results suggest that activation of the forward mode of NCX after Na+-K+ pump activation inhibits Ca2+ mobilization in endothelial cells, thereby modulating vasomotor tone.

Ectopic expression of syncollin in INS-1 beta-cells sorts it into granules and impairs regulated secretion.

Syncollin was first demonstrated to be a protein capable of affecting granule fusion in a cell-free system, but later studies revealed its luminal localization in zymogen granules. To determine its possible role in exocytosis in the intact cell, syncollin and a truncated form of the protein (lacking the N-terminal hydrophobic domain) were stably transfected in insulin-secreting INS-1 cells since these well-studied exocytotic cells appear not to express the protein per se. Studies by subcellular fractionation analysis, double immunofluorescence staining, and electron microscopy examination revealed that transfection of syncollin produced strong signals in the insulin secretory granules, whereas the product from transfecting the truncated syncollin was predominantly associated with the Golgi apparatus and to a lesser degree with the endoplasmic reticulum. The expressed products were associated with membranes and not the soluble fractions in either cytoplasm or the lumens of organelles. Importantly, insulin release stimulated by various secretagogues was severely impaired in cells expressing syncollin, but not affected by expressing truncated syncollin. Transfection of syncollin appeared not to impede insulin biosynthesis and processing, since cellular contents of proinsulin and insulin and the number of secretory granules were not altered. In addition, the early signals (membrane depolarization and Ca(2+) responses) for regulated insulin secretion were unaffected. These findings indicate that syncollin may be targeted to insulin secretory granules specifically and impair regulated secretion at a distal stage.

Differential cytotoxicity of human wild type and mutant alpha-synuclein in human neuroblastoma SH-SY5Y cells in the presence of dopamine.

Parkinson's disease (PD) involves loss of dopaminergic neurons in the substantia nigra and is characterized by intracellular inclusions, Lewy bodies, consisting primarily of aggregated alpha-synuclein. Two substitution mutations (A53T and A30P) in alpha-synuclein gene have been identified in familial early-onset PD. To understand the biological changes that incur upon alpha-synuclein-induced cytotoxicity in the presence of dopamine, the current studies were undertaken. Human SH-SY5Y neuroblastoma cells coexpressing the human dopamine transporter [hDAT], and either wild type (wt) or mutant alpha-synucleins, were treated with 50 microM dopamine (DA). In cells expressing wt or A30P alpha-synuclein, DA accelerated production of reactive oxygen species and cell death as compared to cells expressing A53T or hDAT alone. The increased sensitivity of such cells to DA was investigated by measuring changes in cellular ionic gradient, by atomic absorption spectrometry, and cell metabolism, by high-resolution nuclear magnetic resonance spectroscopy. Both wt and A30P alpha-synuclein caused rapid decrease in levels of intracellular potassium, followed by mitochondrial damage and cytochrome c leakage, with decreased cellular metabolism as compared to cells expressing A53T or hDAT alone. Collapse of ionic gradient was significantly faster in A30P (t(1/2) = 3.5 h) than in wt (t(1/2) = 6.5 h) cells, and these changes in ionic gradient preceded cytochrome c leakage and depletion of metabolic energy. Neither wt nor mutant alpha-synuclein resulted in significant changes in ionic gradient or cellular metabolism in the absence of intracellular DA. These findings suggest a specific sequence of events triggered by dopamine and differentially exacerbated by alpha-synuclein and the A30P mutant.

ET-1 inhibits B-16 murine melanoma cell migration by decreasing K(+) currents.

Cell migration is mediated by ion channels and transporters, and plays crucial roles in a variety of physiological and pathological processes. Previously, our studies have shown that a Ca(2+)-regulated K(+) current exists in B-16 murine melanoma cells, and that endothelin-1 (ET-1) inhibits the K(+) current via a PKC-dependent pathway. In the present study, patch-clamp whole-cell recording and transwell migration assays were used to examine the effects of ET-1 on B-16 murine melanoma cell migration. ET-1 (100 nM in the injection pipette and 10 nM in the incubation medium) decreased the K(+) current amplitude by 33.0 +/- 2.5% and inhibited migration of B-16 cells by 57.4 +/- 9.4%. Similarly, the Ca(2+)-regulated K(+) channel blockers, BaCl(2) and quinidine, decreased the K(+) current by 20.5 +/- 1.0% and 36.6 +/- 1.2%, respectively, and slowed migration of B-16 melanoma cells by 37.1 +/- 8.6% and 42.7 +/- 8.8%, respectively. The effect of ET-1 on the K(+) current and cell migration was simulated by ET-3. In contrast, the K(+) channel opener, diclofenac, increased the K(+) current by 128.8 +/- 11.7%, 257.4 +/- 35.8% at concentrations of 1 and 5 mM, respectively. Likewise, the migration of B-16 murine melanoma cells dramatically increased by 75.6 +/- 12.7% in the presence of 100 microM diclofenac in incubation medium. Furthermore, the ET-1- and ET-3-induced inhibition of K(+) current and migration was abrogated by diclofenac. In the presence of diclofenac, ET-1 only reduced the K(+) current amplitude by 10.6 +/- 1.1%, and slowed B-16 cell migration by only 10.8 +/- 8.9%. The results suggest that the K(+) channel-dependent migration of B-16 melanoma cells is modulated by ET-1. Cell Motil.

Direct inhibition of rat detrusor muscle contraction by erythromycin.

PURPOSE: Detrusor instability is a common problem in the elderly, which is usually treated with anti-cholinergic medication. This study investigates the effect of erythromycin on rat detrusor muscle contractile response to characterise its potential as an alternative inhibitor of bladder muscle contraction. MATERIALS AND METHODS: Strips of rat detrusor muscle were suspended in a perfusion organ bath. The contractile response to direct muscle stimulation, electrical field stimulation (EFS, 0.5-60 Hz), carbachol (10(-5) M), and potassium (10-80 x 10(-3) M) were determined before and after the addition of erythromycin (10(-4)-10(-3) M). The contractile response to carbachol (10(-5) M) in the presence of nifedipine (10(-8) or 10(-6) M) or in calcium-free Kreb's solution was also determined in the absence and presence of erythromycin. RESULTS: Erythromycin 5 x 10(-4) M inhibited the maximum contractile response to EFS, carbachol, and potassium by 38% (P < 0.01), 62% (P < 0.001), and 17% (P < 0.05), respectively, but did not significantly reduce the response to direct muscle stimulation. The atropine-resistant component of EFS-evoked contraction was inhibited by 19.5% (P < 0.01) in the presence of erythromycin. In calcium-free Krebs solution, the maximum contractile response to carbachol was reduced by 42% of control (P < 0.0001) and nifedipine 10(-8) M had no additional effect. When erythromycin 5 x 10(-4) M was added together with nifedipine 10(-8) M, the response to carbachol was inhibited by a further 25% (P < 0.005). CONCLUSIONS: Erythromycin inhibits rat detrusor muscle contraction through the inhibition of calcium influx and the modulation of intracellular calcium movement.

Potassium depletion improves myocardial potassium uptake in vivo.

Potassium depletion (KD) is a very common clinical entity often associated with adverse cardiac effects. KD is generally considered to reduce muscular Na-K-ATPase density and secondarily reduce K uptake capacity. In KD rats we evaluated myocardial Na-K-ATPase density, ion content, and myocardial K reuptake. KD for 2 wk reduced plasma K to 1.8 +/- 0.1 vs. 3.5 +/- 0.2 mM in controls (P < 0.01, n = 7), myocardial K to 80 +/- 1 vs. 86 +/- 1 micromol/g wet wt (P < 0.05, n = 7), increased Mg, and induced a tendency to increased Na. Myocardial Na-K-ATPase alpha(2)-subunit abundance was reduced by approximately 30%, whereas increases in alpha(1)- and K-dependent pNPPase activity of 24% (n = 6) and 13% (n = 6), respectively, were seen. This indicates an overall upregulation of the myocardial Na-K pump pool. KD rats tolerated a higher intravenous KCl dose. KCl infusion until animals died increased myocardial K by 34% in KD rats and 18% in controls (P < 0.05, n = 6 for both) but did not induce different net K uptake rates between groups. However, clamping plasma K at approximately 5.5 mM by KCl infusion caused a higher net K uptake rate in KD rats (0.22 +/- 0.04 vs. 0.10 +/- 0.03 micromol x g wet wt(-1) x min(-1); P < 0.05, n = 8). In conclusion, a minor KD-induced decrease in myocardial K increased Na-K pump density and in vivo increased K tolerance and net myocardial K uptake rate during K repletion. Thus the heart is protected from major K losses and accumulates considerable amounts of K during exposure to high plasma K. This is of clinical interest, because a therapeutically induced rise in myocardial K may affect contractility and impulse generation-propagation and may attenuate increased myocardial Na, the hallmark of heart failure.

Reduction by gabapentin of K+-evoked release of [3H]-glutamate from the caudal trigeminal nucleus of the streptozotocin-treated rat.

Recently, we showed that gabapentin can inhibit a facilitatory effect of substance P (SP) on K(+)-evoked glutamate release in rat trigeminal slices (Maneuf et al., 2001), and we have now examined the effect of gabapentin on glutamate release in the trigeminal slice from the streptozotocin (STZ)-treated rat. 1. At 4 weeks following STZ treatment (50 mg kg(-1) i.p.), blood glucose was increased in the majority of cases, compared to the control level. All the treated animals showed a significant degree (P<0.001) of tactile allodynia (assessed using von Frey filaments) that did not appear to correlate with blood glucose levels. 2. In this study, we demonstrated that, after STZ treatment, 30 microM gabapentin reduced K(+)-evoked release of [(3)H]-glutamate in either normal (11 mM) or high (30 mM) glucose conditions by 24 and 22%, respectively. In the normal rat, gabapentin (up to 100 microM) is ordinarily unable to affect release of glutamate from the trigeminal slice. 3. The uptake of glutamate in Sp5C punches from streptozotocin-treated rats was reduced under normal glucose conditions (41.7% of control), whereas high glucose restored uptake to normal (84.7% of control). 4. The addition of 1 microm substance P potentiated the evoked release of glutamate in both normal (40% increase) and high glucose (28%), and this was blocked by gabapentin (30 microM) in both conditions. It is interesting to speculate that this ability of gabapentin to reduce the release of glutamate in the trigeminal nucleus after streptozotocin treatment may be of relevance to the antihyperalgesic-allodynic actions of the drug.

Protective effects of a potent C5a receptor antagonist on experimental acute limb ischemia-reperfusion in rats.

OBJECTIVES: The capacity of a potent C5a receptor antagonist to inhibit various parameters of local and remote organ injury following lower limb ischemia-reperfusion (I/R) in rats was investigated. METHODS: Rats were subjected to 2 h bilateral hindlimb ischemia and 4 h reperfusion. Drug-treated rats received AcF-[OPdChaWR] (1 mg/kg) iv either 10 min before ischemia or 10 min prior to reperfusion, or orally (10 mg/kg) 30 min prior to ischemia. Levels of circulating creatine kinase (CK), lactate dehydrogenase (LDH), alanine and aspartate aminotransferase (ALT/AST), creatinine, blood urea nitrogen (BUN), polymorphonuclear leukocytes (PMNs), and calcium (Ca(++)) and potassium (K(+)) ions were determined. Other parameters measured included urinary protein levels, muscle edema, and myeloperoxidase (MPO) concentrations in the lung, liver, and muscle along with liver homogenate tumor necrosis factor-alpha (TNF-alpha) concentrations.L RESULTS: imb I/R injury was characterized by significant elevations of CK, LDH, ALT, AST, creatinine, BUN, proteinuria, PMNs, serum K(+), muscle edema, organ MPO, and liver homogenate TNF-alpha concentrations, but a significant reduction in serum Ca(2+) concentrations. When rats were treated with AcF-[OPdChaWR], there were significant improvements in all these parameters. CONCLUSIONS: These results indicate a pivotal role for C5a in inducing local and remote organ injury and suggest a possible new drug therapeutic category for preventing anticipated tissue injury associated with I/R.