Effects of platelet-activating factor on single potassium channel currents in guinea pig ventricular myocytes

Platelet-activating factor (PAF) has been implicated as one of the mediators of cardiac anaphylaxis. This phospholipid has been shown to have numerous effects on a variety of tissues, including the heart. Among these effects are alterations in the resting potential and generation of arrhythmias at very low concentrations. This suggests that PAF may modulate the activity of the background, inwardly-rectifying potassium current (I_K1). Thus, the effects of PAF on I_K1 were examined at the single channel level. Ventricular cells were isolated from adult guinea pig hearts and single channel currents recorded from cell-attached patches. PAF had substantial effects on the single channel currents at sub-nanomolar concentrations (10^–11 to 10^–10 M). PAF initially caused flickering of the channels, followed by a gradual prolonged depression of channel activity. Since these potassium channels play a major role in determining the resting potential and excitability of the cardiac cell, the effects of PAF on I_K1 may play a major role in the deleterious electrophysiological actions of PAF on the heart.Abbreviations I_K1 Inwardly-rectifying background potassium current - Lyso-PAF Lyso-platelet-activating factor - PAF Platelet-activating factor     

Calcium-Dependent Evoked Release of N[3H]Acetylaspartylglutamate from the Optic Pathway

N-Acetylaspartylglutamate (NAAG) is a neuropeptide localized to several putative glutamatergic neuronal systems, including the rodent optic pathway. To determine whether the peptide is released by depolarization, the superior colliculus of the rat was perfused with 2 microCi of [3H]NAAG, then with Krebs-bicarbonate buffer for 1 h, using a microdialysis system. Subsequently, 10-min fractions were collected and analyzed by HPLC for [3H]NAAG. Addition of 100 microM veratridine resulted in a several-fold increase in the evoked release of [3H]NAAG that was virtually abolished by coperfusion with Ca2+-free Krebs buffer containing 1 mM EGTA. When [3H]glutamate was used as the precursor, veratridine depolarization resulted in only an 80% increase in the release of [3H]NAAG. Prior enucleation of the right eye reduced the spontaneous release of [3H]NAAG by 50%, and the veratridine-evoked release by greater than 85%, from the left superior colliculus. These results suggest that NAAG is released upon depolarization and may serve as a neurotransmitter/neuromodulator in the optic tract.     

N-Acetyl-Aspartyl-Glutamate: Regional Levels in Rat Brain and the Effects of Brain Lesions as Determined by a New HPLC Method

Abstract: An isocratic HPLC method to measure endogenous N -acetyl-aspartyl-glutamate (NAAG) and N -acetyl-aspartate (NAA) is described. After removal of primary amines by passage of tissue extracts over AG-50 resin, the eluate was subject to HPLC anion-exchange analysis and eluted with phosphate buffer with absorbance monitored at 214 nm. The retention time for NAA was 5.6 min and for NAAG 11.4 min with a limit sensitivity of 0.1 nmol. The levels of NAA and NAAG were measured in 16 regions of rat brain and in heart and liver. NAAG was undetectable in heart and liver and exhibited 10-fold variation in concentration among brain regions; the highest levels were found in spinal cord. In contrast, low concentrations of NAA were detectable in heart and liver, and the regional distribution of NAA in brain varied only twofold. The regional distribution of NAA and NAAG correlated poorly. To assess the neuronal localization of these two compounds, the effects of selective brain lesions on their levels were examined. Decortication caused a 28% decrease in NAAG levels in the ipsi-lateral striatum while NAA decreased 38%. Kainate lesion of the striatum resulted in a 31% decrease in NAAG in the ipsilateral striatum, whereas NAA fell by 58%. Kainate lesion of the hippocampus resulted in significant decrements in NAAG and NAA in the hippocampus and septum. Transection of the spinal cord at midthorax resulted in a 51% decrease in NAAG levels immediately caudal and a 40% decrease immediately rostral to the lesion; however, NAA decreased only 30% in these areas. These results are consistent with a neuronal localization of NAAG in brain. Combined with the fact that NAAG interacts with a subpopulation of glutamate receptors, these results suggest that NAAG may serve as an excitatory neurotransmitter.     

EFFECTS OF KAINIC ACID ON ION DISTRIBUTION AND ATP LEVELS OF STRIATAL SLICES INCUBATED IN VITRO

Abstract— To determine the mechanism of neurotoxicity of kainic acid, striatal slices (350μ) were incubated in oxygenated Krebs buffer with kainic acid and other depolarizing agents; and the alterations in the uptake and retention of ²²Na⁺, ⁸⁶Rb⁺ (as a measure of K ⁺), ³H_zO and the levels of ATP were determined. The excitatory amino acid, L-glutamate (10 mM) increases striatal slice uptake and retention of Na⁺, K⁺ and H₂O but decreases ATP levels whereas the neuroexcitant, A'-methyl aspartate, increases only Na⁺ and H₂O. Veratridine (100μM), which opens electrogenic sodium channels, and ouabain (100μM), which inhibits Na⁺-K⁺ ATPase, both elevate striatal Na⁺ and H₂O but considerably reduce K⁺ and ATP. The effects of these different depolarizing agents on the parameters examined are consistent with their mechanisms of actions and support the validity of this in vitro method. Although 10mM-kainate significantly depresses striatal K⁺ and ATP, lower concentrations of kainate (5mM-0.1μ) elevate striatal uptake of Na⁺ but do not markedly affect H₂O, K⁺ or ATP. Kainate (10mM-lμM) does not exhibit additivity with 10 mM-glutamate with respect to Na⁺ permeability but does significantly potentiate glutamate's ATP depleting effects. Injection of 10 nmol of kainate into the striatum in vivo causes a reduction in striatal ATP 1 h afterward which is comparable to that occurring in vitro with 10mM-kainate alone or with lower concentrations of kainate (≥1/μM) with 10 mM-glutamate. These results suggest that kainate alone is directly neurotoxic at 10mM or neurotoxic at lower concentrations in combination with the high intrasynaptic levels of glutamate on neurons receiving glutamatergic innervation.     

Changes in plasma zinc,copper, iron,and hepatic metallothionein in adjuvant-induced arthritis treated with cyclosporin

The early changes in hepatic metallothionein (MT) and plasma zinc (Zn), copper (Cu), and iron (Fe) were investigated during the induction of adjuvant (AJ) arthritis in rats in conjunction with cyclosporin (CSA) treatment. Plasma Zn decreased after AJ injection (60% of control values at 8 h), and this was associated with a 4.5-fold increase in hepatic MT at 8 h. Plasma Zn was lowest at 16 h (40% of control), whereas hepatic MT concentrations increased to a maximum of 20-fold at 16 h. Changes in plasma Fe paralleled those of Zn, whereas plasma Cu levels were increased. Plasma metal and hepatic MT concentrations returned toward normal from d 1–7. At d 14, when marked paw swelling was apparent, hepatic MT and plasma Cu were again increased and plasma Zn decreased. Administration of CsA decreased MT induction in rats injected with AJ and also caused a marked recovery in plasma Zn and Fe levels. These changes were small but significant even in the early stages (up to 24 h) after AJ injection and were followed by a sustained improvement in all parameters, corresponding to the nonappearance of clinical arthropathy in CsA-treated rats. TNF-α and IL-6 production by peritoneal macrophages isolated from AJ-injected rats was significantly decreased by CsA treatment at d 7 and 14. The inhibition of hepatic MT induction during acute and chronic inflammation by cyclosporin emphasizes the role of the immune system in altered metal homeostasis in inflammation.     

Exercise hyperventilation in patients with McArdle's disease

This study was undertaken to determine if patients who lack muscle phosphorylase (i.e., McArdle's disease), and therefore the ability to produce lactic acid during exercise, demonstrate a normal hyperventilatory response during progressive incremental exercise. As expected these patients did not increase their blood lactate above resting levels, whereas the blood lactate levels of normal subjects increased 8- to 10-fold during maximal exercise. The venous pH of the normal subjects decreased markedly during exercise that resulted in hyperventilation. The patients demonstrated a distinct increase in ventilation with respect to O2 consumption similar to that seen in normal individuals during submaximal exercise. However their hyperventilation resulted in an increase in pH because there was no underlying metabolic acidosis. End-tidal partial pressures of O2 and CO2 also reflected a distinct hyperventilation in both groups at approximately 70-85% maximal O2 consumption. These data show that hyperventilation occurs during intense exercise, even when there is no increase in plasma [H+]. Since arterial CO2 levels were decreasing and O2 levels were increasing during the hyperventilation, it is possible that nonhumoral stimuli originating in the active muscles or in the brain elicit the hyperventilation observed during intense exercise.