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P Hess

Publications and source records attributed to P Hess.

At least 55 records · Page 3Linked to original sources
PubMed1994

Microscopic heterogeneity in unitary N-type calcium currents in rat sympathetic neurons.

1. Single N-type calcium (Ca2+) channels in rat superior cervical ganglion neurons display complex patterns of activity in both inactivating and non-inactivating gating modes. Unitary currents were elicited by holding the patch at -90 mV and stepping to +30 mV for 740 ms. Barium (110 mM) was used as the charge carrier. The dihydropyridine agonist (+)-202-791 was included in the bath to ensure that single channel recordings showed no L-type Ca2+ channel mode 2 activity. Using this protocol, we characterized three additional patterns of N-type Ca2+ channel activity named: (1) LLP for large unitary current amplitude (i = -0.92 pA) and low open probability (Po = 0.26); (2) SLP for small unitary current amplitude (i = -0.77 pA) and low open probability (Po = 0.25); and (3) SHP for its small unitary current (i = -0.77 pA) and higher open probability (Po = 0.39). 2. Transitions among these patterns of activity occur more slowly than transitions between closed and open states, resulting in significant clustering of like sweeps. Thus, the complicated gating of single N-type Ca2+ channels can be dissected into multiple, independent modes, each with the same reproducible pattern of activity. 3. This heterogeneous activity is not unique to sympathetic neurons, for inactivating (4), non-inactivating (4), SLP (4) and SHP (3 patches) gating modes were also observed in cell-attached patch recordings (n = 4) of single N-type Ca2+ channels in differentiated phaeochromocytoma (PC12) cells. 4. The 1568 sweeps from four single N-type Ca2+ channel recordings that used the same voltage protocol were categorized by mode to determine the frequency of occurrence of each. Of the 54% of sweeps that showed activity, 42% were inactivating and 58% were non-inactivating. The contribution by each mode to the sustained current was estimated using the equation: I = NPoi, where N is the frequency of occurrence of each mode and Po and i are the mean values of open probability and unitary current amplitude respectively. The LLP mode contributed 18%, the SLP mode 16%, and the SHP mode 66% of the sustained whole cell N-type Ba2+ current. 5. The variability in the incidence among these modes in other cell types may resolve some of the controversy surrounding the characterization of N- and L-type whole cell Ca2+ current components in peripheral neurons. In addition, the number of different modes provides a source of plasticity that may be a target of modulation by neurotransmitters and cellular signals.

Animals↗
PubMed1994

Spontaneous mutations at aprt locus in a mammalian cell line defective in mismatch recognition.

Clone B is a CHO cell line that shows a moderate mutator phenotype as a consequence of a defect in mismatch recognition. To identify the classes of mutation that accumulate spontaneously in a functional gene, we isolated and sequenced 54 clone B spontaneous mutants at the adenine phosphoribosyltransferase gene. This spectrum was compared to 42 mutants collected in the parental cells. Rates of AT-->TA transversions and frameshifts were strikingly increased in clone B (almost eight- and sixfold, respectively). Minor increases were also observed for GC-->TA transversions and GC-->AT transition rates. Frameshifts occurred in repeated sequences, and a large proportion were losses of 2 bases occurring in dinucleotide runs of a type similar to microsatellite sequences. AT-->TA transversions clustered in regions of secondary structure and their formation might be explained by slippage-mediated mechanisms. These data indicate that an important function of mismatch recognition is in repair of extrahelical bases generated by misalignment during DNA replication.

Adenine Phosphoribosyltransferase↗
PubMed1994

Major role of the renin angiotensin system in the neointima formation after vascular injury in guinea pigs.

ACE inhibition has been shown to prevent neointima formation after vascular injury. However, it is not known if this effect is due to a specific inhibition of the renin angiotensin system or to another mechanism such as the accumulation of bradykinin. In order to answer this question we compared the effects of maximal effective doses of cilazapril, an angiotensin converting enzyme (ACE) inhibitor, and ciprokiren, a new renin inhibitor, in guinea pigs. Vascular injury was induced by endothelial denudation of the right carotid artery of guinea pigs treated either by saline (control group), cilazapril (30 mg/kg/day) or ciprokiren (24 mg/kg/day). Twelve days after the ballooning, the guinea pigs were sacrificed, the carotid arteries were perfused fixed and neointima formation was evaluated by quantitative morphometry. Both, ciprokiren and cilazapril prevented neointima formation to the same extent (inhibition by 42 and 49%, respectively, p < 0.05). These results suggest that, in guinea pigs, renin inhibition prevents neointima formation to a similar extent as ACE inhibition. Therefore, ACE inhibitors seem to act in this model by inhibiting the renin angiotensin system and not by other effects such as accumulation of bradykinin.

Animals↗
PubMed1994

Endothelin plays a role in the maintenance of blood pressure in normotensive guinea pigs.

The objective of the present study was to evaluate if endothelin plays a role in the maintenance of arterial blood pressure in normotensive guinea pigs. For this purpose, the effects of a new mixed (ETA + ETB) endothelin receptor antagonist, Ro 47-0203 (bosentan), were evaluated in vitro on aortic rings and in anesthetized and conscious guinea pigs. In vitro, bosentan was a potent (pA2 = 7.5) and competitive endothelin receptor antagonist as shown by the parallel rightward shift of the concentration-response curve for endothelin-1 on guinea pig aortic rings in presence of increasing concentrations of bosentan. In vivo, bosentan significantly decreased arterial blood pressure of both anesthetized and conscious guinea pigs. This effect was similar to the effect of BQ-123, a selective ETA receptor antagonist. No additional effect was observed when bosentan was given on top of BQ-123. Neither inhibition of the renin angiotensin system with remikiren, cyclooxygenase inhibition with indomethacin, bradykinin antagonism with Hoe 140, ganglionic blockade with chlorisondamine, parasympathetic inhibition with atropine nor nitric oxide synthase blockade with L-NAME altered the effect of bosentan. In conclusion, the present results show that endothelin contributes to the maintenance of arterial blood pressure in normal normotensive guinea pigs most likely through stimulation of ETA receptors.

Animals↗
PubMed1994

Role of endothelin in the maintenance of blood pressure in conscious rats with chronic heart failure. Acute effects of the endothelin receptor antagonist Ro 47-0203 (bosentan).

BACKGROUND: Endothelin (ET) is a potent vasoconstrictor, and its concentration is increased in patients with heart failure. The purpose of this study was to investigate the role of endothelin in heart failure by use of a rat model. METHODS AND RESULTS: Experiments were performed on rats at 1 through 16 weeks after sham operation or coronary artery ligation. Rats with left ventricular end-diastolic pressures > 15 mm Hg were considered to have chronic heart failure (CHF), while the others were considered to have uncomplicated myocardial infarction (MI). There were increased ET-1 concentrations in CHF rats at weeks 1 to 16 (Sham, 20 +/- 0.5 pg/mL, n = 45; CHF, 31 +/- 2 pg/mL, n = 50; P < .001) and transient increases in ET-3 concentrations at week 1 in both the MI and CHF groups. There were no significant increases in big ET-1 concentrations, suggesting an increased conversion of ET-1 from big ET-1 in the CHF group. At weeks 2 through 8, oral administration of the mixed (ETA and ETB) endothelin receptor antagonist bosentan significantly decreased mean arterial pressure in conscious CHF rats, an effect that increased over time. Furthermore, bosentan had an additive effect to the angiotensin-converting enzyme inhibitor cilazapril. CONCLUSIONS: Endothelin plays a role in the maintenance of blood pressure in CHF rats, as evidenced by the significant reduction in mean arterial pressure after oral administration of bosentan. Therefore, endothelin antagonists may be useful therapeutic agents in the treatment of CHF.

Animals↗
PubMed1994

Oh, say, can you hear?

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Communication Devices for People with Disabilities↗
PubMed1994

War in Gotham City.

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Emergency Medical Services↗
PubMed1994

Where's God?

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Christianity↗
PubMed1994

Experimental carotid thrombosis in the guinea pig.

The aim of our study was to develop a new carotid thrombosis model with an arterial shear rate close to that prevailing in affected arteries of patients with transient ischemic attacks (TIAs) and moderate carotid stenosis and to test various antithrombotic principles. In anaesthetized guinea pigs, carotid blood flow was monitored by a Doppler flow probe and the vessel was damaged by 2 or 3 brief pinches by a surgical forceps. The intravenous effects of aspirin (20 mg/kg), heparin (200 U/kg) and hirudin (500 micrograms/kg) or Ro 44-9883 (0.2 to 1 mg/kg), a new selective non-peptidic GP IIb-IIIa inhibitor were tested. After the damage, blood flow progressively decreased to zero and could regularly and reproducibly be restored by a mechanical shaking of the artery. The occlusive thrombus consisted mainly of platelet aggregates. The estimated shear rate in the damaged carotid artery was in the range of 1500 to 2800 s-1. The resulting cyclic flow variations (CFVs) were obtained in all the guinea pigs and were abolished in 10%, 20% and 60% of the animals treated with heparin, hirudin and aspirin, respectively. Ro 44-9883 abolished dose dependently the CFVs with 100% abolition at 1 mg/kg. Thus reproducible thrombosis without additional stenosis can be generated in the carotid artery of the guinea pig at a lower shear rate than that prevailing in the classical thrombosis models. GPIIb-IIIa blockade showed a higher curative efficacy than inhibition of the cyclooxygenase pathway or that of thrombin generation either through an antithrombin III dependent or independent mechanism.

Acetates↗
PubMed1993

Pursuing the voltage sensor of a voltage-gated mammalian potassium channel.

Ion channels are generally classified as voltage- or ligand-gated channels based upon their ability to respond to a change in the transmembrane voltage or to a specific ligand interaction. The voltage sensor of voltage-gated ion channels is thought to be contained within the fourth putative transmembrane segment, S4, and is characterized by basic residues typically spaced apart. Thus far, a full understanding of all charges contributing to the voltage sensor of voltage-gated potassium channels has been lacking since several neutralization mutants in S4 could not be functionally expressed. By construction of multimeric cDNAs encoding a mammalian RCK1 (Kv1.1) potassium channel, we now report functional expression of all charge neutralizations in the S4 segment, providing a more comprehensive insight into the functioning of the voltage sensor.

Animals↗
PubMed1993

Block by calcium of ATP-activated channels in pheochromocytoma cells.

We have investigated the effects of Ca2+ on Na+ influx through ATP-activated channels in pheochromocytoma PC12 cells using single channel current recordings. Under cell-attached patch-clamp conditions with 150 mM Na+ and 2 mM Ca2+ in the pipette, the unitary current activity showed an open level of about -4.3 pA at -150 mV. The channel opening was interrupted by flickery noise as well as occasional transition to a subconducting state of about -1.7 pA at -150 mV. The open level was decreased with increased external Ca2+, suggesting that external Ca2+ blocks Na+ permeation. We assessed the block by Ca2+ as the mean amplitude obtained with heavy filtration according to Pietrobon et al. (Pietrobon, D., B. Prod'hom, and P. Hess, 1989. J. Gen. Physiol. 94:1-21). The block was concentration dependent with a Hill coefficient of 1 and a half-maximal concentration of approximately 6 mM. A similar block was observed with other divalent cations, and the order of potency was Cd2+ > Mn2+ > Mg2+ not equal to Ca2+ > Ba2+. High Ca2+, Mg2+ and Ba2+ did not block completely, probably because they can carry current in the channel. The block by external Ca2+ did not exhibit voltage dependence between -100 and -210 mV. In the inside-out patch-clamp configuration, the amplitude of inward channel current obtained with 150 mM external Na+ was reduced by increased internal Ca2+. The reduction was observed at lower concentrations than that by external Ca2+. Internal Ba2+ and Cd2+ induced similar reduction in current amplitude. This inhibitory effect of internal Ca2+ was voltage dependent; the inhibition was relieved with hyperpolarization. The results suggest that both external and internal Ca2+ can block Na+ influx through the ATP-activated channel. A simple one-binding site model with symmetric energy barriers is not sufficient to explain the Ca2+ block from both sides.

Adenosine Triphosphate↗
PubMed1993

[Aorto-duodenal fistula--a late complication after infrarenal aortic replacement].

Peripheral atherosclerotic vascular disease is associated in up to 12% with an abdominal aortic aneurysm (AAA). If operation is required AAA is treated in 90% by infrarenal dacron graft implantation. As late complication secondary aortoduodenal fistula is diagnosed in 0.1-4.0%. Mortality in untreated patients is 100%, perioperative mortality depending on operative technique is 17-77%. We present 2 case reports and diagnostic, operative and prophylactic methods.

Aortic Diseases↗
PubMed1993

Surgical treatment of humeral shaft fractures--the Basel experience.

One hundred twenty seven patients with fractures of the humeral shaft were treated by open reduction and internal fixation using 4.5-mm dynamic compression plates (DCP). Seventy one osteosyntheses were performed primarily, 36 following attempted closed reduction, and 20 secondarily after a failed conservative treatment of about 8 weeks. A primary radial nerve palsy was present in 19 patients, and appeared subsequently in four additional patients. One hundred two of the 127 patients could be clinically and radiologically examined 1 year after internal fixation: 89 patients (87.3%) had excellent or good results with full functional recovery. Thirteen patients (12.7%) showed a limited range of motion of either the shoulder or elbow or both. This was mostly because of other fractures of the same limb or persistent neurologic impairment. We observed two transitory postoperative nerve palsies, five early failures of internal fixation because of technical errors, two pseudarthroses and four postoperative infections, which healed with one exception by suction drainage and early removal of the plate. We conclude that a correct plate fixation of humeral shaft fractures in a selected group of patients represents an alternative to conservative treatment with the advantage of greater patient comfort.

Adolescent↗