Asbjørn Røed

Neurotoxic Effects of Root Filling Materials on Rat Phrenic Nerve in vitro

Inhibitory effects of root filling materials on the conduction of action potentials evoked in rat phrenic nerves were evaluated in vitro. Endomethasone and N2 Normal completely and irreversibly inhibited conductance; ProcoSol caused complete but reversible inhibition; Kloroperka N-O caused total inhibition which was sometimes reversed; and AH26 and Diaket showed partial inhibition which was partially reversible.

Signal transduction and gene transcription induced by TFF3 in oral keratinocytes

Trefoil factor family 3 (TFF3) is secreted in saliva. The peptide improves the mechanical and chemical resistance of mucins, and it may act as a motility signal for oral keratinocytes during wound healing. This study aimed to identify novel functions of TFF3 in oral keratinocytes. To achieve this, we used phosphoprotein and messenger RNA (mRNA) arrays to compare TFF3-treated and untreated oral keratinocytes. Analysis of the phosphoprotein array indicated that TFF3 signals through the mitogen-activated protein kinases (MAPKs) c-Jun N-terminal kinase (JNK), p38, and extracellular signal-regulated kinase (ERK1/2), and through the phosphoinositide 3-kinase (PI3K)/protein kinase B (PKB) pathway. Microarray analysis of mRNA showed that TFF3 stimulation induced changes in the expression of genes functionally related to cell death/survival, cell growth and proliferation, and cell movement. The reverse transcription-polymerase chain reaction (RT-PCR) results indicated that the transcription of some immediate-early genes (IEGs) was downregulated, whereas the IEGs FBJ osteosarkoma oncogene (FOS) and C-MYC binding protein (MYCBP2) were transiently upregulated by TFF3 stimulation. Together, the results of the arrays indicate that TFF3 is a modifying factor in pathways regulating cell survival, cell growth and proliferation, and cell migration of oral keratinocytes. Trefoil factor family 3 may therefore promote oral wound healing and it should be considered for the treatment of oral ulcerating diseases, or of other diseases.

Separate sites for the dantrolene-induced inhibition of contracture of the rat diaphragm preparation due to depolarization or to caffeine

Addition of dantrolene 8.5 x 10(-5) M caused a mono-exponential decay of the depolarization contractures caused by inhibition of the sarcolemmal Na,K-ATPase with propranolol 1 mM or by depolarization of the sarcolemma and T tubular membranes with KCl 100 mM. The half-times of the inhibitory effects were 6 s for the propranolol contracture and 11 s for the KCl contracture. The inhibition of both contractures was complete. Inhibition of the caffeine (10 mM) contracture was bi-exponential with half-times of 45 s and 9.5 min. Inhibition was incomplete; 29.6 +/- 5.0% of the contracture tension could not be inhibited. The inhibition of twitch contractions was similar to that of the caffeine contracture, with half-times of 48 s and 9.1 min, and 20.6 +/- 1.2% of the initial twitch tension could not be inhibited. The contracture tensions induced by release of Ca from the mitochondria with dicumarol, and by actin-myosin binding with the sulfhydryl inhibitor, N-ethyl-maleimide, could not be inhibited by dantrolene. The present results indicate that dantrolene inhibits depolarization signals from the sarcolemma and the T tubular membranes, in addition to inhibition of the coupling between the T tubules and the sarcoplasmic reticulum, and of the release of Ca from the sarcoplasmic reticulum. All these effects of dantrolene may contribute to its therapeutic effect in malignant hyperthermia.

Caffeine-induced blockade of neuromuscular transmission and its reversal by dantrolene sodium

Caffeine, 10(2) M, blocked the indirectly stimulated rat phrenic nerve-diaphragm preparation at 37 degrees C. Dantrolene, above 2.25 x 10(-7) M, reversed the blockade. Microelectrode recordings showed a gradual reduction of the end plate potential (EPP) amplitude following a period of facilitation. An increased frequency of miniature (EPPs was still recorded after complete EPP blockade. A presynaptic blockade of stimulus-secretion coupling caused by an effect upon Ca2+ balance is suggested. Caffeine may release and deplete Ca2+ from the smooth endoplasmic reticulum (SER) in the nerve terminals. This Ca2+ may be sequestered by the mitochondria. The blockade suggests that the SER may also supply Ca2+ to another intraterminal release site which is necessary for stimulus-secretion coupling. This site is unaffected by caffeine and dantrolene. The dantrolene reversal may result from inhibition of the caffeine-induced release from the same Ca2+ pool. The facilitatory effects of caffeine were not antagonized by dantrolene and may result from Ca2+ release from another pool.

Inhibitory effect of propranolol on tetanic contraction in rabbit.

The effects of propranolol on electrical and mechanical activity during tetanic stimulation of the diaphragm and leg muscles, and on the heart rate, were studied in the anaesthetized rabbit. Propranolol (from 0.5 mg/kg) reduced the EMG evoked in diaphragm by phrenic nerve stimulation (50/sec) and the EMG and force of contraction during periods of increased respiratory drive obtained by partial tracheal obstruction. The heart rate was lowered by 10-25%. In the indirectly or directly stimulated leg muscles, the drug induced high frequency inhibition of EMG and tetanic contractions (100/sec) without affecting twitch contractions. The inhibitory effect of propranolol on skeletal muscle was probably not caused by beta-adrenergic block, but by stabilization of the sarcolemma. The results suggest that the high frequency inhibitory effect might contribute to the fatigue and reduced work capacity frequently observed when high doses of propranolol are given to man and animals.

Countercurrent Exchange of Heat in the Dog Kidney

The mechanisms of renal heat clearance were studied in anesthetized dogs by recording renal venous and cortical temperatures during step changes of arterial blood temperature induced by infusion of 0.9% saline of room temperature into the renal artery. The venous thermodilution curves were well described by a three-exponential function with average rate constants: k1 = 10.4 min-1, k2 = 2.2 min-1, and k3 = 0.59 min-1, and intercepts at 34%, 44%, and 22%, respectively. The various components were interpreted as follows: The slow component mainly represents heat conduction from inner medullary and perirenal tissue as shown by extrarenal temperature recording and by calculating the heat distribution volume. Local cortical recordings showed that cortex is not a homogeneous compartment, and k2 reflects an average cortical heat clearance, k1 is much higher than blood flow per gram of tissue in any kidney region and results from heat exchange between intrarenal arteries and veins. The arteriovenous diffusion of heat explains the higher temperatures observed in the cortex and the renal medulla than in renal venous blood. The arteriovenous thermodilution technique is unsuited for local and total renal blood flow measurements, because of countercurrent diffusion and heat exchange witli perirenal tissue.

Ca antagonistic and non-specific effects of diltiazem on the rat phrenic nerve diaphragm preparation

The calcium antagonist diltiazem (2.8 X 10(-4) M) blocked the twitches of a rat phrenic nerve diaphragm preparation after a period of twitch potentiation. Its ability to block twitches was greater during indirect than direct stimulation. Experiments on the isolated phrenic nerve indicated that the excitability of the nerve was blocked. Diltiazem (2.3-9.0 X 10(-5) M) caused a similar inhibition of indirectly and directly elicited tetanic contractions and EMG. Experiments with d-tubocurarine and lowered temperature disclosed a separate inhibition at the neuromuscular junction. High Ca2+ did not reverse the diltiazem-affected twitch or tetanic contractions, which suggests that they are non-specific effects. KCl (100 mM)-induced contractures were antagonized at low (2.3-4.5 X 10(-5) M) but not at high (1 mM) concentrations of diltiazem. Diltiazem depressed the initial phase of the two-phasic caffeine (10 mM) contracture and increased and accelerated the slow phase. Diltiazem greatly reduced the amplitude and duration of the caffeine-potentiated KCl contracture, and reduced and delayed the slow phase of the KCl-potentiated caffeine contracture. The effects on the combined contractures (caffeine-induced, KCl-potentiated) were partly antagonized by a high Ca2+ (2.2 X 10(-5) M) solution, which suggests that diltiazem has calcium antagonistic effects.

Enhanced (Na+, K+)-activated ATPase activity after indirect electric stimulation of rat skeletal muscle in vivo

Abstract A significant increase in sarcolemma bound ATPase activity was obtained after indirect electric stimulation of leg muscles in rats. The enzyme activity was assayed on isolated sarcolemma, and the unstimulated leg served as control. Membrane located 5′-nucleotidase was unaffected by the muscle activity.

Comparison of the effects of mercuric chloride and methylmercuric chloride on the isolated phrenic nerve and on the phrenic nerve-diaphragm preparation from the rat

This study compared the effects of HgCl(2) and CH(3)HgCl on the compound action potential of the isolated rat phrenic nerve and the twitch contractions of rat phrenic nerve-diaphragm preparations during direct and indirect stimulation. Both HgCl(2) and CH(3)HgCl, at a concentration of 3.7 x 10(-5)m, inhibited the twitches during indirect stimulation. CH(3)HgCl was slightly more potent than HgCl(2). The inhibition might be explained by a simultaneous inhibition of the phrenic nerve. CH(3)HgCl caused an additional curare-like inhibition at the neuromuscular junction. HgCl(2) potentiated the indirectly elicited twitches before the inhibitory effect ensued. The twitch potentiation was inhibited by low temperature (20 degrees C), high Ca(2+) (10.8 mm) and d-tubocurarine (7.3 x 10(-7)m). It was probably caused by multiple excitation of some of the nerve terminals. Both agents were less efficient at inhibiting the preparations during direct stimulation than during indirect stimulation. However, during direct stimulation, HgCl(2) was a considerably more potent inhibitor than CH(3)HgCl. Both mercury compounds caused a slow increase in the baseline tension. An additional rapid initial phase with HgCl(2) could be partly inhibited by dantrolene (1.5 x 10(-5)m), high Ca(2+) (10.8 x 10(-3)m) or low temperature (20 degrees C), indicating that it was a depolarization contracture. The slow phase was not affected by dantrolene, and may be characterized as a rigor. The effects of HgCl(2) and CH(3)HgCl were irreversible on washing, but they could be partly antagonized by washing plus exposure to dithiothreitol, to keep SH groups in the reduced state.

Selective potentiation of subtetanic and tetanic contractions by the calcium-channel antagonist nifedipine in the rat diaphragm preparation

1. Nifedipine (1.5-3.0 x 10(-5) M) potentiated the (sub)tetanic tension during 10-50 Hz indirect or direct stimulation of the rat diaphragm preparation; the twitch contractions were not potentiated. 2. The effect was antagonized in high Ca2+ (5-10 x normal) solutions. 3. A comparison with the twitch potentiators caffeine (1.0 x 10(-3) M), quinine (1.4 x 10(-5) M) and phenytoin (2.0 x 10(-5) M), showed that only phenytoin, a putative Ca-antagonist, caused a nifedipine-like frequency-dependent potentiation, indicating a Ca-antagonistic rather than an unspecific effect. 4. A similar (sub)tetanic potentiation was found in a K(+)-free solution. 5. The slow development of the potentiation during repetitive stimulation is in accordance with an effect on the slow Ca channels known to be present in mammalian skeletal muscle. 6. A delay of the fatigue-inducing accumulation of K+ in the T tubules, which may occur during a nifedipine-induced reduction of a Ca2(+)-stimulated K+ efflux, as well as in a K(+)-free solution, may explain the effect.