PubMed Health⌕ Search

Biomedical subjects

P Ambühl

Publications and source records attributed to P Ambühl.

7 recordsLinked to original sources
PubMed1998

Chronic hyperosmolality increases NHE3 activity in OKP cells.

This study investigated the effect of chronic hypertonicity on the OKP cell Na/H antiporter, encoded by Na/H exchanger 3 (NHE3). Chronic (48 h) increases in extracellular glucose, mannitol, or raffinose concentration caused a significant increase in Na/H antiporter activity, while increases in urea concentration were without effect. This effect was seen with changes in osmolality of only 20 mOsm/liter, a magnitude that is observed clinically in poorly controlled diabetes mellitus. Increases in mannitol concentration acutely inhibited and chronically stimulated Na/H antiporter activity. The increase in Na/H antiporter activity induced by hypertonic incubation was resistant to 10(-7) and 5 x 10(-6) M but inhibited by 10(-4) M ethylisopropyl amiloride, consistent with regulation of NHE3. In addition, hypertonicity increased total cellular and plasma membrane NHE3 protein abundance twofold, with only a small increase in NHE3 mRNA abundance. We conclude that chronic pathophysiologically relevant increases in tonicity lead to increases in NHE3 protein abundance and activity. This may be responsible for increased proximal tubule apical membrane Na/H antiporter activity in poorly controlled diabetes mellitus, which could then contribute to hypertension, glomerular hyperfiltration and diabetic nephropathy.

Amiloride↗
PubMed1997

Chronic metabolic acidosis enhances NHE-3 protein abundance and transport activity in the rat thick ascending limb by increasing NHE-3 mRNA.

Chronic metabolic acidosis (CMA) is associated with an adaptive increase in the bicarbonate absorptive capacity of the rat medullary thick ascending limb (MTAL). To specify whether NHE-3, the apical MTAL Na/H exchanger, is involved in this adaptation, NHE-3 mRNA was quantified by a competitive RT-PCR using an internal standard which differed from the wild-type NHE-3 mRNA by an 80-bp deletion. CMA increased NHE-3 mRNA from 0.025+/-0.003 to 0.042+/-0.009 amol/ng total RNA (P < 0.005). NHE-3 transport activity was measured as the initial proton flux rate calculated from the Na-dependent cell pH recovery of Na-depleted acidified MTAL cells in the presence of 50 microM HOE694 which specifically blocks NHE-1, the basolateral MTAL NHE isoform. CMA caused a 68% increase in NHE-3 transport activity (P < 0.001). In addition, CMA was associated with a 71% increase in NHE-3 protein abundance (P < 0.05) as determined by Western blot analysis on MTAL membranes using a polyclonal antiserum directed against a cytoplasmic epitope of rat NHE-3. Thus, NHE-3 adapts to CMA in the rat MTAL via an increase in the mRNA transcript that enhances NHE-3 protein abundance and transport activity.

Acidosis↗
PubMed1995

A decrease in angiotensin receptor binding in rat brain nuclei by antisense oligonucleotides to the angiotensin AT1 receptor.

Intracerebroventricular (i.c.v.) injections of antisense oligonucleotides against mRNA of the angiotensin type 1 (AT1) receptor have been shown to reduce blood pressure in spontaneously hypertensive (SHR) rats and angiotensin II-induced drinking in both SHR and Sprague-Dawley (SD) rats. The present investigation was designed to quantify the effect of i.c.v. injections of antisense oligonucleotides to the AT1 receptor mRNA on brain angiotensin receptors using membrane binding and autoradiographic analysis. Control injections contained sense or scrambled oligonucleotides or saline. Three daily injections of antisense oligonucleotides into the third ventricle of SD rats decreased the AT1 receptor number significantly by 25% in a hypothalamic tissue block. AT2 receptors were not altered. Autoradiography showed a decrease in angiotensin receptor number in hypothalamic nuclei and in the anteroventral region of the third ventricle (AV3V) after antisense treatment. AT2 receptors were not reduced indicating the AT1 antisense oligonucleotides were specific. In a second series of experiments, single injections of antisense oligonucleotides into the lateral ventricle of SHR rats were tested. Antisense oligonucleotides produced a significant decrease in receptor number in the same hypothalamic area. Sense and scrambled oligonucleotides did not decrease the receptor numbers significantly. The decreases observed after injection of antisense oligonucleotides were between 15 and 30%. These changes may be sufficient to account for the physiological effects of i.c.v. injections of antisense oligonucleotides to AT1 receptor mRNA.

Analysis of Variance↗
PubMed1994

[7-D-ALA]-angiotensin-(1-7): selective antagonism of angiotensin-(1-7) in the rat paraventricular nucleus.

Microiontophoretic application of both, the octapeptide angiotensin II (Ang II) and its N-terminal heptapeptide angiotensin-(1-7), [Ang-(1-7)], has been shown to increase the firing rate of rat hypothalamic paraventricular neurones. In the present microiontophoretic study, the effect of the angiotensin analogue [7-D-Ala]-Ang-(1-7) on Ang II- and Ang-(1-7)-induced firing rate increase of paraventricular neurones has been tested. While the response to Ang II was unchanged, the response to Ang-(1-7) was effectively blocked by [7-D-Ala]-Ang-(1-7). The results indicate that the Ang-(1-7)-induced excitation of paraventricular neurones may be mediated by a distinct Ang-(1-7)-receptor and that [7-D-Ala]-Ang-(1-7) is a selective antagonist of this receptor.

Action Potentials↗
PubMed1992

Effects of angiotensin II and its selective antagonists on inferior olivary neurones.

On the basis of biochemical and autoradiographic studies it has been shown that the inferior olivary nucleus (ION) contains predominantly angiotensin II (Ang II) receptors of the subtype 2 (AT2). In the present investigation we used microiontophoretic techniques to test the effect of Ang II on the spontaneous firing rate of rat neurones in the ION in vivo. Ang II excited the majority of histologically identified ION neurones. Furthermore, the antagonism of this angiotensin-induced excitation by selective angiotensin receptor blockers of subtype 1 and 2 (AT1 and AT2) was examined. The excitation could be blocked by low doses of the AT2-antagonists PD 123177 and CGP 42112A, whereas the AT1-antagonist DuP 753 was ineffective even at high doses. On a few occasions, however, ejection of the AT1-antagonist resulted in a potentiation of angiotensin-induced excitation. The results suggest that Ang II has an excitatory effect on a considerable number of ION neurones and that this effect is mediated by AT2-receptors.

Angiotensin II↗
PubMed1992

Effects of angiotensin analogues and angiotensin receptor antagonists on paraventricular neurones.

In a previous study we observed that most neurones in the paraventricular nucleus are excited by angiotensin-(1-7). In comparison with angiotensin III this excitatory action was significantly delayed. The aim of the present microiontophoretic study of angiotensin II-sensitive rat paraventricular neurones was to compare the effect of the angiotensin-analogues angiotensin-(1-7), angiotensin-(2-7), angiotensin II and angiotensin III on the spontaneous activity of these neurones and to test angiotensin receptor subtype 1 antagonists (CGP 46027 or DuP 753) and subtype 2 selective antagonists (CGP 42112A and PD 123177) in order to acquire more evidence of the receptor subtype present. As previously observed angiotensin II, angiotensin III and angiotensin-(1-7) excited most neurones. The effect of angiotensin-(1-7) was usually weaker than that of angiotensin II, and in contrast to angiotensin III the latencies were not significantly different. Angiotensin-(1-7) seemed to be active by itself, because its effect was antagonised by angiotensin receptor antagonists. Angiotensin-(2-7) was mostly inactive, although a few cells were excited. Whereas the excitatory effects of angiotensin-(1-7), angiotensin II and angiotensin III could always be inhibited with both angiotensin receptor subtype antagonists 1 and 2, that produced by angiotensin-(2-7) was only weakly antagonised, if at all. Subtype 1 selective antagonists were effective at lower concentrations than selective subtype 2 antagonists.

Angiotensin II↗