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Biomedical subjects

H Knauf

Publications and source records attributed to H Knauf.

At least 91 records · Page 5Linked to original sources
PubMed1978

[Pharmacokinetics of triamterene and its active metabolites in renal insufficiency (author's transl)].

1. After one oral dose of 100 mg triamterene plasma levels of triamterene (TA) and its metabolites hydroxytriamterene (OH-TA) and hydroxytriamterene sulfuric acid ester (OH-TA-ester) were studied in patients with normal and impaired renal function and in patients submitted to hemodialysis. Triamterene and its metabolites were also determined in the urine and the dialysate, respectively. 2. Hydroxytriamterene sulfuric acid ester (OH-TA-ester) representing a phase-II-metabolite of triamterene was found to yield plasma concentrations which were always higher than those of native TA. 3. In decreased renal function the elimination half-lives (t 1/2) of TA and OH-TA-ester were increased yielding elevated plasma levels of TA and its metabolites. The data of t 1/2 for TA and OH-TA-ester correlated with the creatinine clearance in an almost hyperbolic fashion. 4. Dialysance values of about 2 to 4 ml/min were determined for TA and OH-TA-ester.

Adolescent↗
PubMed1977

Selective blockage of the Na+ transport path by Bay g 2821.

A series of transport and electrophysiological experiments were carried out on rat salivery duct epithelium to study the mechanism of action of Bay g 2821 on electrolyte transport at the cellular level. On the basis of the reported data it is suggested that Bay g 2821 blocks Na+ entry into the cell at the luminal rather than at the intersitial membrane of the duct cell.

Adenosine Triphosphatases↗
PubMed1976

[The role of HCO3- ATPase in H+ /HCO3-Secretion (author's transl)].

Active buffer transport, e.g. H+ -secretion by stomach and kidney and HCO3--secretion by pancreas and salivary glands, is linked with the presence of a HCO3-stimulated ATP-Phosphohydrolase. In contrast to (Na+ -k+)-ATPase which is considered to be equivalent to the Na+ pump, the HCO3--ATPase requires only one ion for activation and is insensitive to ouabain. The HCO3--ATPase is found in the plasma membrane of the epithelia, but in contrast to the (Na+ -k+)-ATPase it is located in the luminal cell border. The activity of the HCO3--ATPase changes in parallel along with the rate of active buffer transport, a finding which underlines its importance as a transport enzyme. Several disorders of buffer transport are described which are possibly associated with a defect of the HCO3--ATPase system.

Adenosine Triphosphatases↗
PubMed1976

The effect of spironolactone on transport of Na+, K+ and H+. A microperfusion study in rat main submaxillary duct.

The epithelium of the main excretory duct of the rat submaxillary gland was used as a target tissue for studies on the effect of a spironolactone on electrolyte transport. The spironolactone decreased net Na+ reabsorption by 27% and net K+ secretion by 23%. HCO-3 was found to be about 2-fold accumulated in the duct lumen, which was considered to result from decreased H+ion secretion. The results can be reconciled with an action of spironolactone on 1) the peritubular Na+-K+-exchange mechanism and 2) the functional coupling of Na+ entry from lumen to cell with K+ and H+ transfer from cell to lumen.

Animals↗
PubMed1976

On the mechanism of action of triamterene: effects on transport of Na+, K+, and H+/HCO3- -ions.

The rat salivary duct epithelium, which actively transports Na+, K+, and H+/HCO3- in a manner similar to renal distal tubules, was used as a model tissue to study the mechanism of action of triamterene on electrolyte transport. 10(-4) M triamterene completely blocked Na+ resorption and lowered net K+ secretion to half that of controls, whereas HCO3- accumlated in the lumen, probably due to a decrease in H+ secretion. The rates of K+ and H+/HCO3- transport in the presence of triamterene did not differ from those determined after omission of Na+ from the luminal fluid. This was considered to be evidence against a direct action of triamterene on transport of K+ and H+/HCO3-. Triamterene rapidly and reversibly reduced the transepithelial electrical potential difference. This was due to almost complete abolition of Na+ conductance of the luminal membrane at 10(-4) M triamterene, whereas K+ conductance was not altered. Triamterene, administered in vitro from the interstitial side of the isolated duct epithelium was ineffective even at the highest concentrations. The activities of the Na-K-ATPase, the Mg-ATPase and the microsomal HCO3-ATPase were influenced by 10(-4) M triameterene in a similiar fashion. These effects were clearly demonstrated only in the homogenate of the duct tissue and not in intact cells in the isolated duct preparation. Therefore they were considered unspecific. The transport studied demonstrate a primary effect of triamterene on Na+ entry from lumen to cell. Influences on net K+ and H+/HCO3 transport are secondary consequences of functional coupling between movement of Na+ and movement of K+ and H+ across the luminal cell membrane.

Adenosine Triphosphatases↗
PubMed1976

Non-specific inhibition of membrane-ATPase by amiloride: a comparative in vivo and in vitro study with ouabain.

The submaxillary duct epithelium, which actively transports Na+ (rabbit) and, in addition, K+ and H+/HCO-/3 (rat), was used as a model epithelium to compare the effects of ouabain and amiloride on transport parameters. 1. Ouabain was only effective from the interstitial side, amiloride, however, only from the luminal side. Amiloride induced effects on transport of the ions were seen within less than 1 s, ouabain effects, however, only after minutes. 2. Ouabain inhibited in a parallel fashion the Na+ transport potential and the Na+-K+-ATPase activity. It had no effect on the Mg2+-ATPase and the HCO-/3-ATPase. 3. Amiloride also inhibited the Na+ transport potential and the Na+-K+-ATPase; however, the Na+ transport potential was significantly more sensitive to amiloride than the Na+-K+-ATPase. 4. Amiloride inhibited in a similar fashion the Na+-K+-ATPase, the Mg2+-ATPase and the HCO-/3-ATPase, but did not influence active HCO-/3 secretion. 5. It is concluded that the amiloride induced effects on the membrane ATPases are non-specific.

4-Nitrophenylphosphatase↗
PubMed1976

The role of HCO3-stimulated ATPase in buffer transport.

An ATPase stimulated by HCO-3ions and other oxybases and inhibited by SCN- has been found in main excretory duct of rat submaxillary gland, a tissue, capable of actively secreting HCO-3ions. No such ATPase was found in the rabbit duct, which normally does not secrete HCO-3. The HCO-3ATPase was localized in the plasma membrane fraction of the homogenate, as evidenced by the marker 5'nucleotidase. The activities of the HCO-3ATPase increased in metabolic alkalosis and decreased in metabolic acidosis in parallel to secretion of HCO-3 and K+ ions by the rat salivary duct epithelium. In renal cortex tissue, where HCO-3 is actively reabsorbed respectively H+ is secreted, there was also found a parallel change in the activity of the HCO-3ATPase and the rate of active H+ secretion. These findings provide further evidence that the membrane-bound HCO-3ATPase is involved in active H+/HCO-3 transport. The HCO-3ATPase is not only stimulated by HCO-3 but also by other non transportable oxybases, a finding which indicates H+ rather than HCO-3 being the actively transported component of the buffer system. Small concentrations of K+ ions decrease the Km for HCO-3 and thus yield stimulation of the HCO-3-ATPase. Thport changing in parallel with that of H+/HCO-3 may be taken as indicative for a coupled K+-H+-exchange mechanism to which the HCO-3ATPase is linked.

Adenosine Triphosphatases↗
PubMed1976

[Inhibition of the exchange of Na+ for K+ and and H+ by triamterene (in epithelia)(author's transl)].

The salivary duct epithelium, which actively transports Na+, K+ and H+/HCO3/- similarly to renal distal tubules, was used as a model tissue to study the mechanism of action of triamterene (Jatropus, Dyrenium) on electrolyte transport. Triamterene was only effective when administered from the luminal side of the duct, not from the interstitial side. 10-4 M triamterene completely blocked Na+-reabsorption. At the same time K+ secretion dropped to half of control, whereas HCO-/3 accumulated in the duct lumen following reduced H+ secretion. These changes in electrolyte transport are caused by an inhibition of Na+-entry by triamterene as suggested by measurements of ion permeability of the cell membrane. Triamterene has no specific effect on the membrane-bound ATPase. Since Na+-entry is functionally coupled with exit of K+ and H+ from cell to lumen, impairment of Na+-entry by triamterene necessarily causes reduction of K+ and H+ secretion into lumen.

Adenosine Triphosphatases↗
PubMed1975

Evidence for Na+ independent active secretion of K+ and HCO - 3 by rat salivary duct epithelium.

In order to elucidate whether or not active secretion of potassium and bicarbonate by the rat submaxillary duct epithelium operates independently of sodium reabsorption, Na+ transport was blocked by amiloride, which is known to inhibit Na+ entry from lumen into cell. With 10(-4) M amiloride in HCO - 3 -Ringer at the luminal side, the transepithelial electrical potential difference approached zero, the Na+ conductance of the luminal cell membrane was drastically reduced, and the K+ conductance was significantly reduced. Net K+ secretion was reduced by 80%, whereas net HCO - 3 secretion was significantly increased. The remaining 20% of net K+ secretion proceeded at zero net Na+ transport and in the absence of significant chemical and electrical potential differences between lumen and interstitium of the duct. This active component of net K+ secretion was accompanied by an equal rate of active HCO - 3 secretion. These findings confirm the independence of this active secretion of K+ and HCO - 3 from Na+ transport. They indicate an electrically neutral secretion of K+ and HCO - 3, probably by the postulated luminal K+ -H+ -exchange mechanism. The 80% of net K+ secretion, which were abolished by amiloride together with Na+ reabsorption, seem to be functionally coupled with Na+ transport. The linkage of K+ -to- Na+ is probably mediated by a luminal carrier exchanging Na+ for K+ and H+.

Amiloride↗
PubMed1975

H+ transport and membrane-bound HCO - 3 ATPase in salivary duct epithelium.

An ATPase stimulated by HCO - ions and other oxybases and inhibited by SCN- has been found in main excretory duct of rat submaxillary gland, a tissue, capable of actively secreting HCO - 3 ions. No such ATPase was found in the rabbit duct, which normally does not secrete HCO - 3. The HCO - 3 ATPase was localized in the plasma membrane fraction of the homogenate, as evidenced by the marker 5'-nucleotidase. The activities of the HCO - 3 ATPase increased in metabolic alkalosis and decreased in metabolic acidosis in parallel to secretion of HCO - 3 and K+ ions by the duct epithelium. These findings provide further evidence that the membrane-bound HCO - 3 ATPase is involved in active H+/HCO - 3 transport.

Adenosine Triphosphatases↗
PubMed1975

The separate modes and sites of action of furosemide and amiloride.

The effect of furosemide and amiloride on the transport of sodium, potassium, hydrogen and bicarbonate ions was studied in microperfusion experiments on the main excretory duct of the submaxillary gland of the rat. Furosemide did not impair transport of Na+, K+ and H+/HCO-3. Amiloride, however, completely abolished Na+ transport. Blockade of Na+ transport was accompanied by abolition of passive K+ secretion, whereas the active components of K+ and HCO-3 secretion were not affected. In urinary excretion studies, amiloride, which is known to block sodium transport selectively, was used in order to assess whether furosemide has a distinct effect that is independent of sodium transport. Oral administration of amiloride caused a selective excretion of Na+ in a more alkaline urine with an extremely low K+ concentration. The injection of furosemide caused a copious diuresis of an isotonic urine, in which excretion of Na+ and K+ was balanced by the excretion of Cl- ions. Combined administration of amiloride and furosemide produced summation of the individual effects of both diuretics, indicating that the two drugs had different sites and modes of action. In the presence of furosemide the kidney no longer responded to antidiuretic hormone, which suggested that the urine concentrating mechanism in Henle's loop was blocked by furosemide.

Amiloride↗