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E Schlatter

Publications and source records attributed to E Schlatter.

At least 19 recordsLinked to original sources
PubMed1992

Ion conductances of isolated cortical collecting duct cells.

The study of ion conductances in the intact cortical collecting duct (CCD) with the patch-clamp method is rather difficult. An optimized method to isolate CCD cells from rat kidneys using an in vivo followed by an in vitro enzyme digestion is described. Individual CCD segments were collected after this digestion and incubated in EGTA-buffered medium. This procedure resulted in single cells or cell clusters. These freshly isolated CCD cells were studied with different modifications of the patch-clamp method. Membrane voltages measured in the cell-attached-nystatin configuration were -74 +/- 1 mV (n = 13) and -68 +/- 3 mV (n = 22) in cells isolated from normal and mineralocorticoid-treated rats respectively. These values and those measured with the nystatin-perforated slow-whole-cell configuration (-79 +/- 1 mV, n = 23) are comparable to those measured in principal cells of isolated CCD segments. The cells hyperpolarized after the addition of amiloride and depolarized with the addition of adiuretin to the bath. The amiloride effect was enhanced when cells were isolated from deoxycorticosterone-acetate-treated rats. The cells were strongly depolarized upon elevation of the extracellular K(+)-concentration and did not demonstrate a measurable Cl- conductance. A large-conductance K+ channel (174 pS, n = 5, cell-attached, 145 mmol/l K+ in the pipette; 140 pS, n = 12, cell-free, 3.6 mmol/l K+ in the bath) was seen. It had a very low activity on the cell, but a high open probability when excised into a solution with 1 mmol/l Ca2+ on the cytosolic side.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Properties of the potassium conductances of principal cells of rat cortical collecting ducts.

In this study we examined by impalement techniques properties of the macroscopic K+ conductances in the luminal and basolateral membrane of principal cells from isolated perfused cortical collecting ducts (CCD) of the rat. Both membranes possess a dominating K+ conductance. Compared to their behaviour with K+, both membranes appear much less permeable to NH+4 and Rb+, and the K+ conductances of both membranes are inhibited by these cations. In light of these findings, it is very unlikely that significant amounts of NH+4, which is secreted in the CCD, cross the principal cells as NH+4. Several inhibitors with known effects on K+ channels in patch-clamp studies have been examined. Tetraethylammonium, which inhibits the excised K+ channels of these cells, has no effect on the macroscopic K+ conductances of either membrane. Verapamil, which inhibits the K+ channels in the luminal membrane, acts predominantly on the basolateral membrane K+ conductance in the intact tubule. Therefore, some of the macroscopic properties of the K+ conductances are distinct from those of single channels thus far observed in patch-clamp studies.

Animals↗
PubMed1992

Action of diuretics at the cellular level.

Classification of diuretics is based on their site and mechanism of action in the nephron. The most frequently used substances comprise 1. the mostly proximally acting carbonic anhydrase inhibitors (CAI); 2. the loop diuretics (LD); 3. the early distally acting thiazides (TZ); and 4. the K+ sparing diuretics (KS) acting in the distal tubule. CAI such as acetazolamide inhibit the dehydration of H2CO3 at the luminal membrane, the hydration of CO2 within the proximal tubule cell and the exit of HCO-3 out of the cell. As a result of this proximal reabsorption of HCO-3 is reduced, a slight diuresis and saluresis is induced. The enhanced urinary excretion of HCO-3 will cause a metabolic acidosis. LD inhibit the Na+2Cl-K+ carrier in the thick ascending limb of the loop of Henle (TAL). This produces a marked diuresis and saluresis which is accompanied by enhanced Ca2+, Mg2+, K+ and acid excretion. TZ inhibit the Na+Cl- cotransporter in the early distal tubule. The diuresis is less marked than that induced by LD but the renal losses of K+ are comparable. KS inhibit Na+ channels present in the luminal membrane of the cortical collecting tubule. This leads to a very limited diuresis, but a marked attentuation of renal K+ losses. All diuretics act by inhibiting the admission of Na+ (LD, TZ, KS) or HCO-3 (CAI) into the cell. Their organotropy is merely due to the fact that they are concentrated in tubule fluid by volume reabsorption and by proximal tubule secretion.

Animals↗
PubMed1991

[Regulation of ion conductance in the cortical collecting duct].

In the following, factors will be discussed which regulate the ionic conductances of the luminal membrane of principal cells of the cortical collecting duct. Transport of sodium and potassium, which is mediated via selective sodium- and potassium-channels, is chronically or acutely adjusted to the needs of the salt balance by the hormones aldosterone and adiuretin. In addition, the potassium conductance and thus potassium secretion can be modified by the cellular pH, which results in a direct and reciprocal coupling between potassium and proton excretion in the cortical collecting duct.

Animals↗
PubMed1991

Macula densa cell function.

Studies concerning the sensing step in the tubuloglomerular feedback (TGF) mechanism have been conflicting. To study this step, we measured macula densa (MD) cell volume and membrane potentials in the isolated perfused ascending limb of the loop of Henle with attached glomerulus with MD segments (cTAL-MD). Addition of furosemide reduced cell volume rapidly and the effect could be reversed on removal of the drug. From the time course of cell volume changes hydraulic conductivity could be measured both in the basolateral and apical cell membrane. It was found that the apical cell membrane constituted the main barrier for water flow with a low hydraulic conductance, while the basolateral hydraulic conductance was quite high. Measurements of the basolateral electrical potential in the MD cells have shown a mean electrical potential of -56 mV. This potential was hyperpolarized by the addition of furosemide, the Cl channel blocker NPPB, or during a reduction of luminal NaCl from 150 to 30 mM, and depolarized when bath Cl concentration was reduced from 150 to 30 mM. These results are consistent with the following model for electrolytes transported and similar to the one described in the cTAL [15]. In the luminal cell membrane there is an Na-K-2Cl cotransporter that takes these ions into the MD cells and there is a potassium recycling through a K channel. On the basolateral membrane side there is an Na-K pump and a Cl channel through which chloride is transported out of the MD cell. The Na-K pump activity seems to be only 1/40 of that in the cTAL cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Principal cells of cortical collecting ducts of the rat are not a route of transepithelial Cl- transport.

The rat cortical collecting duct (CCD) exhibits high rates of NaCl reabsorption when stimulated by mineralocorticoid and antidiuretic hormone (ADH). The present study was undertaken to determine if there is significant transcellular Cl- movement across the principal cells of the rat CCD. CCDs were dissected from kidneys of rats that had been injected with deoxycorticosterone (5 mg, i.m.) 2-9 days prior to the experiment. The ducts were perfused in vitro with identical perfusing and bathing solutions, except that 200 pmol.l-1 ADH was added to the bathing solutions. The basolateral membrane voltage (PDbl) of principal cells was -77 +/- 1 mV and the luminal membrane voltage (PD1) was -68 +/- 1 mV (mean +/- SEM, n = 124). Separate impalements with single-barrelled Cl(-)-selective microelectrodes gave an apparent intracellular Cl- activity of principal cells of 17 +/- 2 mmol.l-1. Transepithelial PD and PDbl were unaffected by luminal furosemide, hydrochlorothiazide (HCT), 4-acetamido-4-isothiocyanostilbene2,2-disulphonic acid, (SITS), or the Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB); bath addition of SITS or the Cl- channel blocker diphenylamino-2-carboxylic acid; or replacement of bath HCO3- by Cl-. The intracellular Cl- activity (a(cell)Cl) also remained unchanged with the addition of HCT, SITS or the Cl- channel blockers to either the perfusing or bathing solutions, or with replacement of the bathing solution HCO3-.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1990

The luminal K+ channel of the thick ascending limb of Henle's loop.

In vitro perfused rat thick ascending limbs of Henle's loop (TAL) were used (n = 260) to analyse the conductance properties of the luminal membrane applying the patch-clamp technique. Medullary (mTAL) and cortical (cTAL) tubule segments were dissected and perfused in vitro. The free end of the tubule was held and immobilized at one edge by a holding pipette kept under continuous suction. A micropositioner was used to insert a patch pipette into the lumen, and a gigaohm seal with the luminal membrane was achieved in 455 instances out of considerably more trials. In approximately 20% of all gigaohm seals recordings of single ionic channels were obtained. We have identified only one single type of K+ channel in these cell-attached and cell-excised recordings. In the cell-attached configuration with KCl or NaCl in the pipette, the channel had a conductance of 60 +/- 6 pS (n = 24) and 31 +/- 7 pS (n = 4) respectively. In cell-free patches with KCl either in the patch pipette or in the bath and with a Ringer-type solution (NaCl) on the opposite side the conductance was 72 +/- 4 pS (n = 37) at a clamp voltage of 0 mV. The permeability was 0.33 +/- 0.02 . 10(-12) cm3/s. The selectivity sequence of this channel was: K+ = Rb+ = NH4+ = Cs+ greater than Li+ much greater than Na+ = 0; the conductance sequence was K+ much greater than Li+ much greater than Rb+ = Cs+ = NH4+ = Na+ = 0. In excised patches Rb+, Cs+ and NH4+ when present in the bath at 145 mmol/l all inhibited K+ currents out of the pipette. The channel kinetics were described by one open (9.5 +/- 1.5 ms, n = 18) and by two closed (1.4 +/- 0.1 and 14 +/- 2 ms) time constants. The open probability of this channel was increased by depolarization. The channel open probability was reduced voltage dependently by Ba2+ (half maximal inhibition at 0 mV: 0.07 mmol/l) from the cytosolic side. Verapamil, diltiazem, quinine and quinidine inhibited at approximately 1 mumol/l -0.1 mmol/l from either side. Similarly, the amino cations lidocaine, tetraethylammonium and choline inhibited at 10-100 mmol/l. The channel was downregulated in its open probability by cytosolic Ca2+ activities greater than 10(-7) mol/l and by adenosine triphosphate greater than or equal to 10(-4) mol/l. The open probability was downregulated by decreasing cytosolic pH (2-fold by a decrease in pH by less than or equal to 0.2 units).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Vasopressin and mineralocorticoid increase apical membrane driving force for K+ secretion in rat CCD.

Cortical collecting ducts (CCD) from untreated Sprague-Dawley rats were perfused and bathed in vitro with modified Krebs-Ringer solutions. Arginine vasopressin (AVP;100 microU/ml) in the bathing solution hyperpolarized the transepithelial voltage (PDT, mV) from -2.3 +/- 0.7 (control) to -6.0 +/- 1.1 (n = 22) and decreased the transepithelial resistance from 64 +/- 7 to 54 +/- 7 omega.cm2 (n = 21). AVP depolarized the basolateral membrane voltage of principal cells (PDbl) only slightly (but significantly by paired statistical comparison) from -85 +/- 1 to -84 +/- 1 mV (n = 9), with a fall in the fractional resistance of the apical membrane (FRa) from 0.82 +/- 0.03 to 0.77 +/- 0.05 (n = 9). Luminal amiloride (10 microM) produced no change in FRa in the absence of AVP, but in the presence of AVP increased FRa to the same level observed in the absence of AVP. The changes with AVP were significantly less than those observed by us previously in deoxycorticosterone (DOC)-treated animals (E. Schlatter and J. A. Schafer. Pfluegers Arch. 409:81-92, 1987), indicating that the observed synergism between DOC and AVP in stimulating Na+ absorption is attributable to a greater increase in the Na+ conductance in the apical membrane of principal cells with AVP in the DOC-treated CCD than in the normal. Furthermore, we have calculated that the depolarization of apical membrane voltage resulting from the increased Na+ conductance produced by either or both AVP and DOC increases the driving force for K+ exit across the apical membrane in proportion to the previously measured increase in secretion. This increase in driving force may be sufficient to explain the increased K+ secretion produced by these hormones with no change in the apical membrane K+ conductance.

Amiloride↗
PubMed1989

Macula densa cells sense luminal NaCl concentration via furosemide sensitive Na+2Cl-K+ cotransport.

The macula densa cells of the juxtaglomerular apparatus probably serve as the sensor cells for the signal which leads to the appropriate tubuloglomerular feedback response. The present study reports basolateral membrane voltage (PDbl) measurements in macula densa cells. We isolated and perfused in vitro thick ascending limb segments with the glomerulus, and therefore the macula densa cells, and the early distal tubule still attached. Macula densa cells were impaled with microelectrodes under visual control. PDbl was recorded in order to examine how these cells sense changes in luminal NaCl concentrations. The addition of furosemide, a specific inhibitor of the Na+2Cl-K+ cotransporter in the thick ascending limb, to the lumen of the perfused thick ascending limb hyperpolarized PDbl from -55 +/- 5 mV to -79 +/- 4 mV (n = 7). Reduction of NaCl in the lumen perfusate from 150 mmol/l to 30 mmol/l also hyperpolarized PDbl from -48 +/- 3 mV to -66 +/- 5 mV (n = 4). A Cl- concentration step in the bath from 150 mmol/l to 30 mmol/l resulted in a 24 +/- 4 mV (n = 4) depolarization of PDbl. This depolarization of PDbl was absent when furosemide was present during the Cl- concentration step. These data suggest that the macula densa cells sense changes in luminal NaCl concentration via coupled uptake of Na+ and Cl-.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Piretanide-dextran and piretanide-polyethylene glycol interact with high affinity with the Na+ 2 Cl- K+ cotransporter in the thick ascending limb of the loop of Henle.

Piretanide blocks the Na+ 2Cl- K+ cotransporter protein in the thick ascending limb (TAL) of the loop of Henle reversibly. When tested from the luminal side in isolated perfused cTAL segments it leads to a half maximal inhibition (IC50) of the equivalent short circuit current (Isc) at a concentration of 10(-6) mol/l. From the basolateral side it has no effect on Isc up to 10(-4) mol/l. The present study was designed to search for high affinity blockers of the Na+ 2Cl- K+ cotransporter with large molecular weight in an attempt to use these macromolecules for antibody-labelling or affinity separation of this transport-protein. Amino-ethyl-dextran or amino-ethyl-polyethylene glycol (M.W. 5kd) were coupled to isothiocyanato-piretanide (ISO-PIR) at room temperature in DMSO. The resulting compounds dextran-sulfonylurea-piretanide (PIR-DEX) and polyethylene glycol-sulfonylurea-piretanide (PIR-PEG) (M.W. 5.38kd) were purified and tested in isolated perfused cTAL segments. IC50 values for ISO-PIR, PIR-DEX and PIR-PEG were estimated from dose response curves after their addition to the lumen or bath perfusate, respectively. ISO-PIR, PIR-DEX and PIR-PEG acted from the lumen side at 3.10(-6), 6.10(-6) and 2.10(-6) mol/l. The inhibitory effect was easily reversible. From the basolateral side no effect for any compound was seen at up to 10(-4) mol/l. In clearance experiments PIR-DEX was given to female Wistar rats as an i.v. bolus (25 mumol/kg) and the diuretic urine was collected. After dialysis (exclusion limit 2.5kd) the dialysed urine and the dialysate were tested in isolated perfused cTAL segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Stimulation of NaCl secretion in the rectal gland of the dogfish Squalus acanthias.

1. The rectal gland of the dogfish (Squalus acanthias) secretes NaCl when stimulated by a hormone related to vasointestinal peptide. 2. Patch clamp and microelectrode techniques are used to examine the changes in membrane conductances occurring with hormonal stimulation. 3. The conductance of the "resting" cell is dominated by basolateral K+ channels. 4. Hormonal stimulation "opens" apical Cl- channels. 5. This opening of apical chloride channels appears to be mediated by cAMP-dependent phosphorylation of pre-existing closed channels.

Animals↗
PubMed1987

Electrophysiological studies in principal cells of rat cortical collecting tubules. ADH increases the apical membrane Na+-conductance.

The mechanism of ion transport across principal cells of rat cortical collecting tubules (CCT) and its regulation by vasopressin (ADH) has been studied in the isolated perfused tubule. To amplify the response to ADH rats were treated with 5 mg I. M. desoxycorticosterone 4-9 days prior to the experiments. Addition of 2 X 10(-10) mol X l-1 ADH increased the transepithelial voltage from -5.1 +/- 0.7 mV to -16.1 +/- 1.4 mV (n = 37) and decreased the transepithelial resistance from 51 +/- 4 omega cm2 to 39 +/- 2 omega cm2 (n = 33). Optical and functional differentiation of impalements of principal and intercalated cells was made and only data of principal cells are presented. ADH depolarized the apical membrane from 79 +/- 1 mV to 66 +/- 2 mV (n = 26) and decreased the fractional resistance of the apical membrane from 0.76 +/- 0.04 to 0.70 +/- 0.04 (n = 13). These ADH effects were prevented by 10(-5) or 10(-4) mol X l-1 luminal amiloride which hyperpolarized the apical membrane when added in the presence or absence of ADH. Apical and basolateral membranes were dominated by large K+ conductances and addition of 3 mmol X l-1 barium to bath or lumen perfusates increased transepithelial resistance almost two-fold, whereas luminal amiloride increased the transepithelial resistance only by 26-35%. Ouabain (0.5 mmol X l-1, bath) depolarized the basolateral membrane and decreased its K+ conductance. These effects were prevented by the simultaneous presence of apical amiloride suggesting that the only route of Na+ entry into the principal cells occurred via the amiloride sensitive Na+ conductance. We conclude that ADH stimulates Na+ reabsorption and K+ secretion in the rat CCT primarily by increasing the Na+ conductance in the apical cell membrane.

Amiloride↗
PubMed1987

Potassium channels in the basolateral membrane of the rectal gland of the dogfish (Squalus acanthias).

Previous studies in isolated, in vitro perfused rectal gland tubules (RGT) have revealed that the basolateral membrane possesses a K+ conductive pathway. In the present study, we have utilized the patch clamp technique in RGT segments to characterize this pathway. The basolateral membrane was approached with patch pipettes at the open end of in vitro perfused segments. Recordings were obtained in cell-attached as well as in excised inside-out patches. In cell-attached patches with the pipette filled with a KCl solution (274 mmol/l) and the bath containing NaCl shark Ringer (275 mmol/l), inward K+ currents (from pipette into cell) with a mean slope conductance of 123 +/- 26 pS (n = 3) were observed. We were unable to generate outward K+ currents at high depolarizing (cell more positive) clamp voltages. This indicates inward rectification of this channel. To examine the rectification properties further, excised (inside out) patches were exposed to K+ concentration gradients, directed out of, as well as into the pipette. With NaCl in the pipette and KCl in the bath, K+ outward currents were observed. The current-voltage (IV) relation revealed Goldman-type rectification, with a mean single channel conductance of 185 +/- 28 pS (n = 7) at high positive voltages (linear range of the IV curve). The single-channel permeability coefficient for K+ was 0.26 +/- 0.04 X 10(-12) cm3/s (n = 7). In the reversed experiment (pipette KCl, bath NaCl), inward currents of similar kinetics and amplitude were obtained. The single channel conductance was 146 +/- 21 pS (n = 7) at high negative voltages (linear range of the IV curve).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Potassium channels in the basolateral membrane of the rectal gland of Squalus acanthias. Regulation and inhibitors.

The present study examines the influences of pH and Ca2+ and several putative inhibitors on the basolateral K+ channel of the rectal gland of Squalus acanthias. Excised membrane patches were examined using the patch clamp technique. It is shown that reduction of the calcium activity on the cytosolic side to less than 10(-9) mol/l has no detectable inhibitory effect on this channel. Conversely, increase in calcium activity to some 10(-3) mol/l reduced the activity of this channel. Variations in cytosolic pH had only a moderate effect on the current amplitude: alkalosis by one pH unit increased and acidosis reduced the single current amplitude by some 15%. Several inhibitors were tested in excised patches when added to the cytosolic side. Ba2+ (approximately 5 X 10(-3) mol/l), quinine (approximately 10(-3) mol/l), quinidine (approximately 10(-4) mol/l), lidocaine (approximately equal to 1 mmol/l), tetraethylammonium (approximately 10 mmol/l), Cs+ (approximately 10 mmol/l), and Rb+ (approximately 20 mmol/l) all blocked this K+ channel reversibly. We conclude that the basolateral K+ channel of the rectal gland is distinct from other epithelial K+ channels inasmuch as it is not stimulated by Ca2+ directly, but that it is qualitatively similar to many other known K+ channels with respect to its sensitivity towards blockers.

Animals↗
PubMed1987

Chloride channels in the luminal membrane of the rectal gland of the dogfish (Squalus acanthias). Properties of the "larger" conductance channel.

The rectal gland of the dogfish (Squalus acanthias) secretes chloride via a chloride channel present in the apical cell membrane. Using the patch clamp technique in isolated perfused rectal gland tubules, two types of chloride channels are demonstrable in the apical membrane of cyclic AMP treated tubule segments. A small channel of about 11 pS and another channel of 40-50 pS are present. The small channel is described in the succeeding report. With NaCl on both sides (excised patches) the current amplitude of the larger channel is an almost linear function of the voltage (+/- 50 mV). However, the open probability of this channel is grossly reduced at negative clamp potentials (corresponding to cell hyperpolarization). Therefore, the macroscopic Cl- current through this channel is reduced with hyperpolarization on the cytosolic side. An analysis of time constants of this channel reveals that at depolarized voltages two open and two closed time constants of about 1 ms and of about 10 ms, respectively, are demonstrable. With hyperpolarized voltages the larger open state time constant is reduced significantly. This type of chloride channel is blocked reversibly by diphenylamine-2-carboxylate (10(-4) mol/l) and by 5-nitro-2-(3-phenylpropylamino)-benzoate (10(-5) mol/l). The channel is selective for Cl- over Na+ and K+ as well as over Br-. It is, however, permeable for NO3-. Since this channel is very rare or absent in nonstimulated rectal gland tubules, it is very likely that this type of channel is responsible for hormone and cAMP dependent chloride secretion in this organ.

Animals↗
PubMed1987

The "small" conductance chloride channel in the luminal membrane of the rectal gland of the dogfish (Squalus acanthias).

Besides the "larger" Cl- channel, with a single channel conductance of about 45 pS, a "small" channel was observed in the luminal membrane of the dogfish rectal gland. In cell excised (inside out) patches with NaCl solution on both sides, the latter channel had a single channel conductance of 11 +/- 1 pS (n = 21), and its current-voltage relationship was linear in the voltage range +90 to -90 mV. The open state probability increased moderately with negative clamp potentials. Ionic replacement studies revealed a high selectivity of Cl- over gluconate, sulfate, and iodide, whereas bromide was permeable to some extent. Also the channel is impermeable for Na+. The Cl- channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoate did not affect this "small" conductance Cl- channel. It can be concluded that the luminal membrane of stimulated rectal gland cells possesses two types of Cl- channels, which differ markedly in their characteristics.

Animals↗
PubMed1986

Cl(-)-channel blockers in the thick ascending limb of the loop of Henle. Structure activity relationship.

On the basis of our findings with diphenylamine-2-carboxylate we have searched for compounds which possess an even higher affinity for the Cl(-)-channels in the basolateral membrane of the thick ascending limb of the loop of Henle. To quantity the inhibitory potency, we performed measurements of the equivalent short circuit current, corresponding to the secondary active transport of Cl- and measurements of the voltage across the basolateral membrane. A survey of 219 compounds reveals that relatively simple modifications in the structure of diphenylamine-2-carboxylate led to very potent blockers such as 5-nitro-2-(3-phenylpropylamino)-benzoate which inhibits the short circuit current half maximally (IC50) at 8 X 10(-8) mol/l. A comparison of the structural formula and the respective IC50 values leads to several empirical conclusions: The potent compounds are lipophilic due to the apolar residue (e.g. phenyl- or cycloalkyl group). Replacing this part of the molecule by an aliphatic chain (up to 4 C-atoms) leads to inactive compounds. Most of the inhibitors are secondary amines. Linking other than with -NH- between the phenyl ring and the benzoic acid results in inactive compounds. Tertiary amines, such as in case of 2-(N,N-diphenylamine)benzoic acid or N-methylphenylamine-benzoic acid are poorly active. The carboxylate group of the benzoate moiety must be in ortho position to the amino group. Introduction of substituents into the benzoate moiety e.g. -NO2 (in meta position to the carboxylate group), or by -Cl (in para position to the carboxylate group) results in an increase of inhibitory potency. A -CH2-, -C2H4-, -C3H6- spacer between the amino bridge and the phenyl ring increases the affinity for the Cl(-)-channel by several orders of magnitude. The above described structure activity relationship renders it likely that these chloride channel blockers possess several sites of interaction: The negatively charged carboxylate group, the secondary amine group which probably carries a positive partial charge, and for the very potent agents (nos. 130, 143, 144, and 145) an additional negative partial charge at the respective -Cl or -NO2 substituent. Finally, also an apolar interaction with an cycloalkyl or cycloaryl residue seems to be required, and this site of interaction has a defined spacing from the secondary amino nitrogen.

Animals↗