bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elevated D‐glucose induces insulin insensitivity in human umbilical endothelial cells isolated from gestational diabetic pregnancies
Authors: Sobrevia L. , Yudilevich D. L. , Mann G. E. 
Published: September 2004

The effects of human insulin and elevated D‐glucose on L‐arginine transport and synthesis of nitric oxide (NO) and prostacyclin (PGI2) have been investigated in human umbilical vein endothelial cells isolated from gestational diabetic pregnancies.
The increase in the Vmax for L‐arginine transport (9.0 ± 1.1 pmol (μg protein)−1 min−1) in diabetic endothelial cells cultured in 5 mM D‐glucose was unaffected following 24 h exposure to 25 mM D‐glucose.
Gestational diabetes‐induced increases in basal intracellular cGMP and L‐citrulline levels (inhibitable by L‐NAME) and [Ca2+]i were unaffected by elevated D‐glucose. In contrast, PGI2 release was inhibited in diabetic cells exposed to either 5 or 25 mM D‐glucose.
Elevated D‐glucose attenuated histamine (10 μM, 5 min)‐stimulated accumulation of cGMP and L‐citrulline in endothelial cells isolated from gestational diabetic pregnancies.
The membrane hyperpolarization (‐79 ± 0.9 mV) sustained in diabetic endothelial cells in culture was insensitive to elevated D‐glucose.
Elevated D‐glucose abolished the stimulatory effect of human insulin (1 nM, 8 h) on L‐[3H]leucine incorporation in diabetic endothelial cells cultured in 5 mM D‐glucose.
Human insulin reduced the elevated rates of L‐arginine transport and cGMP accumulation in diabetic cells cultured in 5 mM D‐glucose but failed to reduce increased rates of transport or NO production in cells exposed to 25 mM D‐glucose or cycloheximide.
Our findings demonstrate that hyperglycaemia impairs the actions of human insulin on umbilical vein endothelial cells isolated from gestational diabetic pregnancies. Changes in insulin sensitivity and/or its signalling cascade may be affected by hyperglycaemia associated with gestational diabetes, resulting in insulin resistance in endothelial cells derived from the fetal vasculature.
Mechanisms of force inhibition by halothane and isoflurane in intact rat cardiac muscle
Authors: Hanley Peter J. , Loiselle Denis S. 
Published: September 2004

We investigated the mechanisms underlying the negative inotropic effect of the volatile anaesthetics halothane and isoflurane using twenty‐two intact, right ventricular trabeculae of rat. [Ca2+]i was measured qualitatively using either fluo‐3 or fura‐2, loaded into the cytosol via the acetoxymethyl (AM) ester form. Diastolic sarcomere length was adjusted to 2.1‐2.2 μm and experiments were performed at 21‐23°C.
We investigated the mechanisms underlying the negative inotropic effect of the volatile anaesthetics halothane and isoflurane using twenty‐two intact, right ventricular trabeculae of rat. [Ca2+]i was measured qualitatively using either fluo‐3 or fura‐2, loaded into the cytosol via the acetoxymethyl (AM) ester form. Diastolic sarcomere length was adjusted to 2.1‐2.2 &#181;m and experiments were performed at 21‐23°C.
The ability of halothane and isoflurane to induce Ca2+ release from the sarcoplasmic reticulum of quiescent trabeculae was examined. When the superfusate was Ca2+ and Na+ free (thereby preventing Na+‐ Ca2+ exchange and Ca2+ influx), 2 % halothane, but not 4 % isoflurane, evoked a transient increase in [Ca2+]i.
Halothane and isoflurane produced reversible, dose‐dependent changes in cellular autofluorescence, the pattern of which was consistent with an increase in concentration of the reduced forms of nicotinamide adenine nucleotides and flavoproteins. This observation supports the putative inhibitory action of volatile anaesthetics at the site of Complex I of the mitochondrial electron transport chain.
Addition of the fatty acid hexanoate, a substrate that can be metabolized in the face of Complex I inhibition, did not appreciably attenuate the anaesthetic‐induced negative inotropy; however, it greatly diminished autofluorescence changes.
To determine whether direct actions of the volatile anaesthetics on the contractile system contributed to the negative inotropy, external [Ca2+] was varied to modulate the amplitude of the Ca2+ transient. In the presence of 2 % halothane or 4 % isoflurane, restoration of the peak Ca2+ transient to control levels did not restore peak force. Moreover, halothane (1 %) and isoflurane (1.6 %) each reduced maximal Ca2+‐activated force (attained using ryanodine tetani and a high external [Ca2+]) by around 15 %.
We conclude that the negative inotropic actions of halothane and isoflurane on intact cardiac muscle reflect both reduced availability of Ca2+ and decreased responsiveness of the contractile system to Ca2+. The inhibitory action of the volatile anaesthetics on mitochondrial function does not contribute significantly to the negative inotropy but may lead to changes in cellular autofluorescence and misinterpretation of fluorescent Ca2+ indicator signals.
Differential effects of noradrenaline on evoked, spontaneous and miniature IPSCs in rat cerebellar stellate cells
Authors: Kondo Satoru , Marty Alain 
Published: September 2004

The modulation by noradrenaline (NA) of synapses among stellate cells was investigated in rat cerebellar slices by using presynaptic loose cell‐attached recording and postsynaptic whole‐cell recording.
NA increased the frequency of spontaneous IPSCs recorded from stellate cells without changing their mean amplitude.
NA increased the firing rate of stellate cells. This effect persisted after blocking ionotropic glutamate receptors and GABA receptors, indicating that it was independent of synaptic input.
The effects of NA on action potential frequency were mimicked by the β‐receptor agonist isoprenaline but not by the α‐receptor agonist 6‐fluoro noradrenaline, and they were not blocked by the α‐receptor antagonist phentolamine, indicating that they were mediated by β‐receptors.
In paired recordings of connected stellate cells, NA slightly decreased the success rate of synaptic transmission. A small decrease in mean IPSC amplitude (excluding failures) and a slight increase in latency were also observed in NA.
These results show that, while NA increases the number of action potential‐dependent IPSCs by increasing the firing rate of stellate cells, it actually reduces the probability of evoked release. Since previous studies showed that NA increases the rate of miniature IPSCs in this preparation, we conclude that different mechanisms underly the modulation by NA of action potential‐dependent and action potential‐independent transmitter release.
Alkaline secretion by frog gastric glands measured with pH microelectrodes in the gland lumen
Authors: Debellis Lucantonio , Caroppo Rosa , Frömter Eberhard , Curci Silvana 
Published: September 2004

In the present work we have measured the pH of the secreted fluid within the gland lumen of isolated but intact gastric mucosa of Ranaesculenta. Tissues were mounted in a double chamber allowing continuous perfusion of the mucosal and serosal compartment, and the measurements were made with double‐barrelled pH glass microelectrodes inserted into the glands from the serosal surface under microscopic inspection.
During inhibition of H+ secretion by cimetidine (100 μm) the luminal gland pH (pHgl) averaged 7.60 ± 0.05 pH units (mean ±s.e.m.; n= 35), a value significantly higher than bath solution pH (7.45 ± 0.02; P < 0.001) and also higher than intracellular pH of oxyntopeptic cells (pHi), which averaged 7.53 ± 0.06 (n= 18).
Stimulation of acid secretion with histamine (500 μm) reversibly decreased pHgl to values which could be as low as 2.5. Together with electrophysiological criteria this response was routinely used to verify the proper location of the microelectrode tip within the gland lumen.
Stimulation with carbachol (100 μm) or pentagastrin (50 μm) in the presence of cimetidine rapidly and reversibly increased pHgl by 0.10 ± 0.01 pH units (n= 24; P < 0.001) and 0.09 ± 0.02 pH units (n= 6; P < 0.05), respectively.
The observation that gastric gland fluid is more alkaline than the bath solutions and that carbachol or pentagastrin further alkalinize it strongly suggests that oxyntopeptic cells participate in gastric alkaline secretion at least under cholinergic stimulation.
Long‐term synaptic plasticity between pairs of individual CA3 pyramidal cells in rat hippocampal slice cultures
Authors: Debanne Dominique , Gähwiler Beat H. , Thompson Scott M. 
Published: September 2004

Long‐term potentiation (LTP) and depression (LTD) were investigated at synapses formed by pairs of monosynaptically connected CA3 pyramidal cells in rat hippocampal slice cultures.
An N‐methyl‐D‐aspartate (NMDA) receptor‐mediated component of the unitary EPSP, elicited at the resting membrane potential in response to single action potentials in an individual CA3 cell, could be isolated pharmacologically.
Associative LTP was induced when single presynaptic action potentials were repeatedly paired with 240 ms postsynaptic depolarizing pulses that evoked five to twelve action potentials or with single postsynaptic action potentials evoked near the peak of the unitary EPSP. LTP induction was prevented by an NMDA receptor antagonist.
Associative LTD was induced when single presynaptic action potentials were repeatedly elicited with a certain delay after either 240 ms postsynaptic depolarizing pulses or single postsynaptic action potentials. The time window within which presynaptic activity had to occur for LTD induction was dependent on the amount of postsynaptic depolarization. LTD was induced if single pre‐ and postsynaptic action potentials occurred synchronously.
Homosynaptic LTD was induced by 3 Hz tetanization of the presynaptic neuron for 3 min and was blocked by an NMDA receptor antagonist.
Depotentiation was produced with stimulation protocols that elicit either homosynaptic or associative LTD.
Recurrent excitatory synapses between CA3 cells display associative potentiation and depression. The sign of the change in synaptic strength is a function of the relative timing of pre‐ and postsynaptic action potentials.
Mechanosensitive cation channels mediate afferent arteriolar myogenic constriction in the isolated rat kidney
Authors: Takenaka Tsuneo , Suzuki Hiromichi , Okada Hirokazu , Hayashi Koichi , Kanno Yoshihiko , Saruta Takao 
Published: September 2004

In order to assess ionic mechanisms mediating renal afferent arteriolar myogenic constriction, experiments were performed using isolated perfused hydronephrotic rat kidneys.
Increasing pressure progressively constricted the afferent arteriole (‐0·26 ± 0·02 % mmHg−1, n= 21, r= 0·97). Gadolinium (10 μM), a mechanosensitive cation channel blocker, abolished this myogenic constriction. However, high potassium media (30 mM) constricted the afferent arteriole in the presence of gadolinium.
Lowering extracellular sodium concentration gradually attenuated afferent arteriolar myogenic constriction. In the perfusate containing 50 mM sodium, the myogenic response was arrested.
Afferent arteriolar myogenic constriction was prevented in calcium‐free perfusate or by the L‐type calcium channel blocker diltiazem (10 μM).
Our present findings provide evidence that increasing pressure gates mechanosensitive cation channels on the afferent arteriole, thereby eliciting membrane depolarization and activating voltage‐dependent calcium channels.
Involvement of interleukin‐1, prostaglandins and mast cells in rectal distension‐induced colonic water secretion in rats
Authors: Eutamene H. , Theodorou V. , Vergnolle N. , Comera C. , Fioramonti J. , Bueno L. 
Published: September 2004

In vivo rectal distension (RD) induces a neurally mediated colonic net water hypersecretion in rats. Interleukin‐1β (IL‐1β) also induces neural colonic water hypersecretion involving the release of prostaglandins (PGs) and a mast cell degranulation in rats. This study investigated in vivo the role of IL‐1, PGs and mast cells in RD‐induced colonic hypersecretion.
Proximal colonic net water flux was determined using [14C]polyethylene glycol (PEG) 4000 (mol. wt, 4000) in anaesthetized rats. On strips taken from the distal colon: (i) a histological analysis was performed to determine the number of mucosal mast cells (MMC); and (ii) histamine levels were measured by radioimmunoassay after stimulation with compound 48/80.
RD induced a net colonic water secretion that was blocked by i.c.v. administration of IL‐1ra (an IL‐1 receptor antagonist) and indomethacin, and by systemic treatment with doxantrazole and indomethacin. RD decreased the number of resident mast cells and the release of histamine from the distal colonic strips. Moreover, using SDS‐PAGE immunoblotting the expression of IL‐1β was detected in the brain.
These results suggest that, in rats, RD induces colonic net water hypersecretion by the activation of a neuro‐immunological reflex pathway, involving brain IL‐1β, PG release and peripheral mast cell degranulation.
Effect of probenecid on breathing movements and cerebral clearance of prostaglandin E2 in fetal sheep
Authors: Walker David W. , Pratt Naomi 
Published: September 2004

Intravenous infusion of probencid (79‐160 mg kg−1) into unanaesthetized fetal sheep (127‐143 days gestation) in utero significantly decreased the incidence and amplitude of spontaneous breathing movements, but did not change the incidence of low voltage electrocortical (ECoG) activity, plasma prostaglandin E2 (PGE2) concentrations, blood gases or pH.
In fetuses pretreated with paracetamol (350 mg kg−1) to inhibit PG synthase activity, infusion of probenecid did not change the mean incidence or amplitude of breathing movements, indicating that the inhibitory effect of probenecid on breathing movements required the presence of active PG synthesis.
Probenecid infusion in four unanaesthetized fetuses significantly increased the PGE2 concentrations in cisternal cerebrospinal fluid (CSF) by 6.6 ± 1.5‐fold (P < 0.05).
In pentobarbitone‐anaesthetized, exteriorized fetuses, probenecid infusion decreased the clearance of [3H]PGE2 from CSF during ventriculo‐cisternal perfusion of artificial CSF containing [3H]PGE2.
These results suggest that there is active transport of PGs from CSF to blood in fetal sheep from at least 127 days gestation. Inhibition of this transport results in the accumulation of PGs within interstitial fluid of the brain, one effect of which is to suppress the spontaneous activity of the respiratory centres.
Non‐genomic action of the mineralocorticoid aldosterone on cytosolic sodium in cultured kidney cells
Authors: Gekle Michael , Silbernagl Stefan , Wünsch Stefan 
Published: September 2004

The mineralocorticoid aldosterone is essential for the regulation of electrolyte homeostasis, extracellular volume and blood pressure. As a steroid hormone the classical way of action is genomic. Previously we reported a non‐genomic action of aldosterone on cytosolic Ca2+ and pH in renal epithelial (MDCK) cells. In parallel, aldosterone induces Zn2+‐sensitive cytosolic acidification when extracellular Na+ is absent.
We now show that aldosterone (EC50, 7 × 10−11 mol l−1) induces a non‐genomic increase in cytosolic sodium in MDCK cells. The membrane‐impermeable aldosterone‐bovine serum albumin (BSA) conjugate exerted the same effect. The effect of aldosterone was completely abolished by inhibition of Na+‐H+ exchange with ethyl‐isopropanol amiloride (EIPA). Aldosterone‐induced Na+ influx exceeded H+ efflux more than 10‐fold.
Omission of extracellular Ca2+, inhibition of protein kinase C or pretreatment with pertussis toxin reduced the effect of aldosterone significantly. Zn2+ (IC50, 3·3 × 10−6 mol l−1), but not ouabain, abolished the increase in Na+ almost completely.
The aldosterone‐induced increase in cytosolic sodium was accompanied by an EIPA‐ and Zn2+‐sensitive cell swelling.
Thus, physiological concentrations of aldosterone induce a non‐genomic increase in cytosolic sodium concentration by activation of Na+‐H+ exchange. Aldosterone exerts its effect, at least in part, at the plasma membrane via interaction with a G‐protein‐coupled mechanism.
The simultaneous activation of the acidification mechanism and Na+‐H+ exchange by aldosterone allows a dramatic sodium influx without excessive changes in cytosolic pH and leads to changes in cell volume.
AMPA receptor activation and phosphatase inhibition affect neonatal rat respiratory rhythm generation
Authors: Ge Qing , Feldman Jack L. 
Published: September 2004

We investigated the role of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA) receptors and their regulation in affecting respiratory‐related neurones in a neonatal rat medullary slice that spontaneously generates respiratory‐related rhythm and motor output in the hypoglossal (XII) nerve.
Bath application of the AMPA receptor antagonist 1‐(4‐aminophenyl)‐4‐methyl‐7,8‐methylenedioxy‐5H‐2,3‐benzodiazepine (GYKI) completely blocked XII nerve activity, as well as respiratory‐related synaptic drives in neurones within the preBötzinger Complex (preBötC), site of rhythm generation in the slice.
Local application of GYKI to the preBötC blocked respiratory rhythm. Local application of AMPA to the preBötC increased rhythm frequency and depolarized respiratory‐related neurones.
In the presence of tetrodotoxin (TTX), GYKI completely blocked the inward current induced by local application of AMPA, but not that induced by kainate.
Local application of okadaic acid, a membrane‐permeable inhibitor of phosphatase 1 and 2A, to the preBötC increased the frequency of respiratory motor discharge.
Intracellular application of microcystin, a membrane‐impermeable inhibitor of phosphatase 1 and 2A, enhanced endogenous inspiratory drive and exogenous AMPA‐induced current (in the presence of TTX) in preBötC inspiratory neurones. Both the enhanced inspiratory drive and the increased AMPA‐induced current were completely blocked by GYKI.
We suggest that AMPA receptor activation and AMPA receptor modulation by phosphorylation are crucial for the rhythm generation within the preBötC.
Developmental changes in expression of ion currents accompany maturation of locomotor pattern in frog tadpoles
Authors: Sun Q.‐Q. , Dale N. 
Published: September 2004

The K+ currents of spinal neurons acutely dissociated from Xenopus larvae were studied and compared with those of neurons dissociated from Xenopus embryos.
The density of total outward current in the larval and embryonic neurons remained the same from stage 37/38 to stage 42.
Almost all neurons at stage 42 expressed a fast activating Ca2+‐dependent K+ current (IKCa) that was largely absent from embryonic neurons. Whereas IKCa became larger and more prevalent during development, the delayed rectifier K+ currents were down‐regulated.
About 53% of IKCa was selectively blocked by iberiotoxin which had no effect on the delayed rectifier K+ currents or the K+ currents of embryonic neurons.
The firing properties of neurons isolated from embryos were unchanged by iberiotoxin. However, the toxin greatly increased the frequency of firing in larval neurons.
Iberiotoxin extended the duration of ventral root bursts during fictive swimming in larvae at stages 41 and 42 but had no effect at stage 40. The progressive expression of IKCa thus contributed to burst termination.
We have found that changes in expression of outward current closely correlate with the maturation of the motor pattern during development. At a time when the motor pattern has a need for a burst‐terminating mechanism, the larval neurons express a channel with properties appropriate for such a role.
Short‐term haemodynamic variability in the conscious areflexic rat
Authors: Létienne Robert , Barrès Christian , Cerutti Catherine , Julien Claude 
Published: September 2004

Similtaneous measurements of arterial pressure and cardiac output (n= 8), mesenteric blood flow (n= 7) or hindquarters (n= 8) blood flow were performed during 1 h periods in conscious rats, before and after acute pharmacological blockade of the autonomic, renin‐angiotensin and vasopressin systems. In the latter condition (areflexic state), arterial pressure was maintained with a continuous infusion of noradrenaline.
In the areflexic state, spontaneous fluctuations in arterial pressure were markedly exaggerated, especially depressor episodes. At the onset of these falls in arterial pressure, there was an abrupt and transient decrease in stroke volume and cardiac output. Systemic vasodilatation then developed while cardiac output returned to normal. Regional vasodilatations were also delayed from the onset of the falls in arterial pressure and were usually large enough to maintain blood flow.
Both time and frequency domain analyses confirmed that changes in systemic and regional vascular conductances lagged by about 1 s behind arterial pressure changes.
These results indicate that, in the absence of neurohumoral influences, autoregulatory‐like mechanisms become dominant in the control of systemic and regional circulations and contribute to exaggeration of the spontaneous short‐term variability of arterial pressure.
Reflex control of splanchnic blood volume in anaesthetized dogs
Authors: Noble B. J. , Drinkhill M. J. , Myers D. S. , Hainsworth R. 
Published: September 2004

In chloralose‐anaesthetized, artificially ventilated dogs, the splenic pedicle was tied and the carotid sinuses were vascularly isolated and perfused at controlled pressures. In Series 1 experiments, the hepatosplanchnic circulation was perfused through the abdominal aorta with a tie on the aorta separating it from the caudal circulation, which was perfused through the femoral arteries. The two circulations were drained from cannulae in the inferior vena cava and the femoral veins, with a tie on the inferior vena cava separating the two. In Series 2, the splanchnic circulation drained from the portal vein. In both series, inflows and outflows were measured and integrated to derive volume changes. Capacitance responses were assessed during constant flow, and capacitance plus passive responses were obtained during constant pressure perfusion.
In Series 1, an increase in carotid sinus pressure (from 8 to 26 kPa) during constant flow and constant pressure perfusion increased hepatosplanchnic volume by 2.5 and 5.7 ml (kg body weight)−1, respectively. The volume of the subdiaphragmatic circulation did not increase during constant flow, but during constant pressure it increased by 2.0 ml (kg body weight)−1.
In Series 2, increasing carotid pressure during constant flow and constant pressure increased the volume of the splanchnic circulation by 0.5 and 4.2 ml (kg body weight)−1, respectively.
These results confirm that carotid baroreceptor stimulation causes larger volume changes during constant pressure perfusion than during constant flow perfusion. Also, the active capacitance change in the splanchnic circulation is small in relation to the passive response. We propose that in dogs (following splenic ligation), the major active capacitance control is from the liver. However, large passive changes in splanchnic volume occur due to changes in flow.