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Biomedical subjects

R Greger

Publications and source records attributed to R Greger.

At least 109 records · Page 6Linked to original sources
PubMed1987

Atrial natriuretic peptide stimulates salt secretion by shark rectal gland by releasing VIP.

Salt secretion by the isolated perfused rectal gland of the spiny dogfish shark, Squalus acanthias, is stimulated by synthetic rat atrial natriuretic peptide (ANP II) as well as extracts of shark heart, but not by 8-bromo-cyclic guanosine 5'-monophosphate. Cardiac peptides have no effect on isolated rectal gland cells or perfused tubules, suggesting that stimulation requires an intact gland. The stimulation of secretion by ANP II is eliminated by maneuvers that block neurotransmitter release. These include: perfusion with procaine (10(-2) M), perfusion with high Mg2+ (9.5 mM) and low Ca2+ (0.5 mM) concentrations, and addition to the perfusate of the calcium channel blockers nifedipine (10(-6)M), diltiazem (5 X 10(-5)M), or verapamil (10(-4)M). Cardiac peptides stimulate the release of vasoactive intestinal peptide (VIP), known to be present in rectal gland nerves, into the venous effluent or perfused glands in parallel with their stimulation of salt secretion, but the release of VIP induced by ANP II is prevented by perfusion with procaine. Cardiac peptides thus appear to regulate rectal gland secretion by releasing VIP from neural stores within the gland. It is possible that other physiological effects of these hormones might be explained by an action to enhance local release of neurotransmitters.

Adenosine↗
PubMed1987

Loop diuretics.

Loop diuretics such as furosemide, piretanide, and bumetanide bind reversibly to the Na+2Cl-K+ carrier. This transporter is responsible for the uptake of Cl- into the thick ascending limb segment. As a consequence, these compounds reduce or abolish NaCl reabsorption in this nephron segment and lead to a decreased interstitial hypertonicity and thus to a reduced water absorption. Apart from these profound effects, loop diuretics also inhibit Ca2+ and Mg2+ reabsorption in the thick ascending limb in a manner which is still not clear. They also increase urinary K+ excretion by an increase in distal tubule NaCl and water delivery and probably also by the reduction of K+ reabsorption which goes on under in vivo conditions in the thick ascending limb segment. Finally, by the reduction of the transport work in the thick ascending limb, these compounds reduce dramatically the substrate and oxygen dependence of this nephron segment.

Animals↗
PubMed1987

[Pathophysiology of renal ischemia].

Renal ischaemia results, early in its course, in cell swelling of those tubule segments which are specifically susceptible to damage. These segments are the straight proximal tubules in the outer stripe of the outer medulla and the medullary thick ascending limb of the loop of Henlé in the outer and inner stripe of the outer medulla. One causal predisposing factor for both nephron segments is the sharp decline in the partial pressure of oxygen in the outer medulla. Another important cause for the vulnerability of the thick ascending limb is its strict dependence on a continuous supply of metabolic substrates. The cell swelling caused by ischaemia can be explained, for all nephron segments, as an unchanged uptake of Na+ across the luminal membrane in the face of a reduced pump rate of the basolateral (Na+ + K+)-ATPase. The swelling can be prevented if, for example, in the thick ascending limb the Na+ uptake is inhibited by furosemide. In addition to cell damage by cell swelling, other pathomechanisms are operative in ischaemia. One such mechanism is the damage caused by oxygen radicals. The concentration of these radicals is increased during ischaemia, especially during the initiation of reperfusion. Additionally, the concentration of radical scavengers such as glutathion, is reduced during ischaemia. Future work is needed to define more closely the damage produced by oxygen radicals in terms of lipid peroxidation, ATP and enzyme degradation.

Animals↗
PubMed1986

Torasemide inhibits NaCl reabsorption in the thick ascending limb of the loop of Henle.

Torasemide (1-isopropyl-(4-(3-methylphenylamino)pyrid-3-yl)urea) is a new diuretic. The present study examines the effects of this substance in the isolated perfused thick ascending limb (TAL) of mouse and rabbit kidney. In cortical TAL segments of the rabbit, torasemide added to the lumen perfusate led to a fall in equivalent short circuit current ( = transepithelial voltage divided by transepithelial resistance, which corresponds to the rate of chloride reabsorption) with a half maximal inhibition concentration of 3 X 10(-7) mol/l. This effect was accompanied by a hyperpolarization of the luminal and basolateral membrane from -78 to -81 mV and from -72 to -81 mV, respectively. A similar hyperpolarization of both membrane voltages was also observed in medullary TAL segments of the mouse. Torasemide, added to the basolateral perfusate of cortical TAL segments of the rabbit, also inhibited the equivalent short circuit current. However, 3 X 10(-5) mol/l were necessary for a half maximal inhibition. The fall in the equivalent short circuit current was accompanied by a significant increase in transepithelial resistance from 34 to 38 omega cm2, by an increase in the fractional resistance of the basolateral membrane, and by a hyperpolarization mainly of the basolateral membrane. Again, similar results were obtained in the medullary TAL segment of the mouse. The strong inhibitory effect of torasemide from the lumen side can be explained by an interference with the Na+ 2Cl-K+ carrier in the luminal membrane. In fact, torasemide apparently is structurally related to furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

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↗
PubMed1986

A voltage-dependent ionic channel in the basolateral membrane of late proximal tubules of the rabbit kidney.

The patch-clamp method was applied to the lateral membrane of late proximal tubules of the rabbit kidney. Tubule segments were cannulated on one side by a perfusion system. At the noncannulated end of the tubules, the lateral membrane was accessible to a patch pipette. In cell-attached, as well as cell-excised (presumably inside-out oriented) membrane patches, a voltage sensitive channel was observed. The open-state probability of this channel increased with depolarizing potentials. In cell-excised patches bathed with NaCl-Ringer on both sides, the single channel conductance g was 28.0 +/- 1.2 pS (n = 10). With KCl-Ringer in the pipette and NaCl-Ringer in the bath g was 24.7 +/- 1.3 pS (n = 7) and the current-voltage curve crossed the axis at 0 mV. Therefore, the channel does not discriminate between K+ and Na+ ions. Replacing half of NaCl by mannitol on the bath side yielded a permeability for cations about twice as high as for Cl-. The channel could be reversibly blocked by diphenylamine-2-carboxylate (DPC), whereas its inhibition by SITS was only partially reversible. In cell-attached patches, the channel was nearly inactivated at zero clamp potential, but became active when the membrane patch was depolarized. The significance of this nonselective channel for proximal tubule cell function is still unclear. It could be involved in the contraluminal exit mechanism of various anions. However, it could also play a role in cell volume regulation processes.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1986

Effects of ouabain and temperature on cell membrane potentials in isolated perfused straight proximal tubules of the mouse kidney.

In isolated perfused segments of the mouse proximal tubule, the potential difference across the basolateral cell membrane (PDbl) was determined with conventional microelectrodes. Under control conditions with symmetrical solutions it amounted to -62 +/- 1 mV (n = 118). The potential difference across the epithelium (PDte) was -1.7 +/- 0.1 mV (n = 45). Transepithelial resistance amounted to 1.82 +/- 0.09 k omega cm (n = 28), corresponding to 11.4 +/- 0.6 omega cm2. Increasing bath potassium concentration from 5 to 20 mmol/l depolarized PDbl by +24 +/- 1 mV (n = 103), and PDte by +1.6 +/- 0.1 mV (n = 19). Thus, the basolateral cell membrane is preferably conductive to potassium. Rapid cooling of the bath perfusate from 38 degrees C to 10 degrees C led to a transient hyperpolarization of PDbl from -60 +/- 1 to -65 +/- 1 mV (n = 21) within 40 s followed by gradual depolarization by +18 +/- 1% (n = 14) within 5 min. The transepithelial resistance increased significantly from 1.78 +/- 0.11 k omega cm to 2.20 +/- 0.21 k omega cm (n = 15). Rapid rewarming of the bath to 38 degrees C caused a depolarization from -61 +/- 2 mV (n = 17) to -43 +/- 2 mV (n = 16) within 15 s followed by a repolarization to -59 +/- 2 mV (n = 10) within 40 s. Ouabain invariably depolarized PDbl. During both, sustained cooling or application of ouabain, the sensitivity of PDbl to bath potassium concentration decreased in parallel to PDbl pointing to a gradual decrease of potassium conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Na+ selective channels in the apical membrane of rabbit late proximal tubules (pars recta).

Using the patch-clamp technique, Na+ selective channels were observed in the luminal membrane of rabbit straight proximal tubule segments. In the cell-attached configuration (NaCl-Ringers in pipette and bath) influx of Na+ ions from the pipette into the cell through fluctuating channels was observed. The current-voltage curve of these Na+ channels yielded a zero-current potential of 84.3 +/- 30.9 mV (n = 10), reflecting the electrochemical driving force for Na+ influx under resting conditions. The single channel conductance was 12.0 +/- 2.1 pS (n = 13). In inside-out oriented cell-excised patches the single channel conductance was not significantly different with NaCl-Ringers on both sides. At clamp potentials ranging from +50 mV to -50 mV the single channel current was ohmic and channel kinetics were independent of the voltage. With KCl-Ringers on the bath side (corresponding to cell interior), the zero current potential was 62 +/- 19 mV (n = 4), indicating a high selectivity of Na+ over K+ ions. Addition of 10(-5) mol/l amiloride to the bathing solution decreased the mean channel open time slightly. This effect was more pronounced with 10(-4) mol/l amiloride, whereas the single channel conductance was unaffected by the diuretic. 10(-3) mol/l amiloride caused a complete block of the channel. It is concluded that amiloride sensitive Na+ channels, with similar properties to those observed in tight epithelia, contribute to Na+ reabsorbtion in the straight portion of proximal tubules.

Amiloride↗
PubMed1985

Diphenylamine-2-carboxylate, a blocker of the Cl(-)-conductive pathway in Cl(-)-transporting epithelia.

The present study examines the effects of diphenylamine-2-carboxylate (DPC) in Cl(-)-transporting epithelia. This substance blocks reversibly the Cl(-)-conductance present under normal circumstances in the basolateral membrane of the thick ascending limb of the loop of Henle (TAL) and in the apical membrane of shark rectal gland tubules (RGT). This leads to a reduction in active NaCl reabsorption (TAL) and NaCl secretion (RGT) respectively, as measured by the equivalent short circuit current. The cells hyperpolarize as the membrane voltage drifts from the control value (some compromise between the chemical potential of Cl- and K+) towards the chemical potential of K+. The resistance of the basolateral (TAL) or apical membrane (RGT) increases and this leads to a moderate increase in transepithelial resistance. In addition, the Cl(-)-concentration step induced membrane voltage changes, which can be produced under control conditions, disappear in the presence of the blocker. Finally, experiments in excised membrane patches indicate that this substance inhibits the single current events of individual Cl(-)-channels.

Animals↗
PubMed1985

Cl- -channels in the apical cell membrane of the rectal gland "induced" by cAMP.

Isolated rectal gland tubules (n approximately equal to 1000) of dogfish (Squalus Acanthias) were perfused in vitro. Individual channels in the apical and basolateral cell membrane were recorded with the patch clamp method. K+-channels were present in excised membrane patches of the basolateral membrane in stimulated (dbcAMP + forskolin + adenosine) and in nonstimulated state. Cl- -channels were found only in patches of the apical cell membrane when the tubule was stimulated. Cell attached recordings and simultaneous transepithelial PD measurements were obtained while the segment was stimulated. It is shown that concomitant with the increase in lumen negative PD "silent" membrane patches of the apical cell membrane suddenly develop Cl- -channel activity. It is concluded that stimulation of rectal gland tubules "activates" Cl- -channels in the apical cell membrane.

Animals↗
PubMed1985

cAMP increases the basolateral Cl- -conductance in the isolated perfused medullary thick ascending limb of Henle's loop of the mouse.

The effect of cAMP on transepithelial and transmembrane potential differences and resistances was examined in isolated in vitro perfused mouse medullary thick ascending limbs of Henle's loop (mTAL). The effects of furosemide and barium were tested. Stimulation of NaCl transport by ADH 10(-9) + dbcAMP 4 X 10(-4) + forskolin 10(-6) mol X l-1 (paired experiments) resulted in: a) an increase in transepithelial potential difference, referenced to the grounded bath, from +6.7 +/- 0.3 mV to +12.0 +/- 0.4 mV (n = 47); b) a decrease in transepithelial resistance from 25 +/- 1 omega cm2 to 20 +/- 1 omega cm2 (n = 47); c) a depolarization of the basolateral membrane by 12 mV and of the apical membrane by 7 mV (n = 36); d) a decrease in the fractional resistance of the basolateral membrane from 0.27 +/- 0.05 to 0.15 +/- 0.06 (n = 12). Furosemide (10(-4) mol X l-1) abolished the active transepithelial transport potential and hyperpolarized the basolateral membrane potential to values which were similar in both control and cAMP treated mTAL segments. Barium increased the transepithelial resistance and depolarized PDb1 to similar values in both functional states. An increase in the fractional conductance of the basolateral membrane was also seen, if, prior to the cAMP treatment, the luminal Na+2Cl-K+ cotransport was inhibited by furosemide. Thus, we propose that stimulation of active NaCl reabsorption in the mTAL segment of the mouse by ADH, mediated via cAMP, increases primarily the basolateral chloride conductance.

Animals↗
PubMed1984

Potassium activity in cells of isolated perfused cortical thick ascending limbs of rabbit kidney.

The Na+2Cl-K+ cotransporter in the apical membrane of the cortical thick ascending limb of the Henle's loop (cTAL) of rabbit nephron utilizes the electrochemical gradient for Na+ to transport K+ and Cl- against an unfavorable electrochemical gradient from lumen to cell interior. In the present study attempts are made to measure intracellular K+ activity (a cell K+) under control conditions and after inhibition of the cotransport system by furosemide (50 X 10(-6) mol X l-1). 70 cTAL segments of 55 rabbits were perfused in vitro. Conventional Ling-Gerard and K+-selective microelectrodes were used to measure the PD across the basolateral membrane (PDbl) as well as the PD sensed by the single barrelled K+-selective electrode (PDK+). PDbl was -64 +/- 1 (n = 65) mV and PDK+ + 15 +/- 1 (n = 32) mV under control conditions. The positive PDK+ value, significantly different from zero, indicates that a cell K+ is higher than predicted for passive distribution. The estimate for a cell K+ obtained from PDbl and PDK+ was 113 +/- 8 mmol X l-1. Furosemide lead to the previously reported hyperpolarization of PDbl by 17 +/- 4 (n = 13) mV and to a reduction of PDK+ from 15 +/- 1 to 5 +/- 1 (n = 20) mV. The a cell K+, obtained from this set of data, was 117 +/- 9 mmol X l-1, and was not different from the control value. The present data indicate that a cell K+ is significantly above Nernst equilibrium under control conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias). II. Effects of inhibitors.

Rectal gland tubule (RGT) segments of the spiny dogfish (Squalus acanthias) were perfused in vitro. The effects of inhibitors of known mode of action on transepithelial PD (PDte resistance (Rte), the PD across the basolateral membrane (PDbl), the fractional resistance of this membrane (FRbl), and intracellular activities of NA+, Cl-, K+ (apha cell) were examined. Furosemide (5 x 10(-4) mol x 1(-1)) reduced PDte from -12 +/- 0.7 to -2.3 +/- 0.2 mV (n = 63), hyperpolarized PDbl from -71 +/- 1.3 to -79 +/- 0.9 mV (n = 59), FRbl decreased from 0.2 +/- 0.03 to 0.13 +/- 0.01 (n = 21), alpha cell cl- fell from 38 +/- 4 to 11 +/- 2 mmol x 1(-1) (n = 21), alpha cell Na+ fell from 37 +/- 4 to 17 +/- 2 mmol x 1(-1) (n = 12) and alpha cell K+ was constant [113 +/- 14 vs. 117 +/- 15 mmol x 1(-1) (n = 6)]. Furosemide exerted its effects within some 20-40s. Its action was completely reversible. Analysis of the time courses revealed that the furosemide induced initial fall in alpha cell cl- was approximately twice as rapid when compared to that of alpha cell Na+. Ba2+ 0.5 mmol x 1(-1) (bath) reduced PDte from -7.1 +/- 1.2 to -4.1 +/- 0.6 mV (n = 24), increased Rte from 18 +/- 2 to 22 +/- 2.5, omega cm2 (n = 14). PDbl depolarized from -75 +/- 2 to -48 +/- 2 mV (n = 42), FRbl increased from 0.2 +/- 0.02 to 0.34 +/- 0.04 (n = 14) and alpha cell K+ increased from 143 +/-28 to 188 +/- mmol x 1(-1) (n = 4). Ouabain (50 x 10(-6) mol x 1(-1), bath) reduced PDte from -12 +/-2 to -3 +/- 0.5 mV (n = 9), Rte increased from 18 +/- 3 to 21 +/- 3 omega cm2 (n = 5). PDbl depolarized from -67 +/- 4 to -26 + 3 mV (n = 14), FRbl increased from 0.23 +/- 0.04 to 0.45 +/- 0.05 (n = 6), alpha cell K+ fell only slightly from 135 +/- 15 to 112 +/- 30 mmol x 1(-1) (n = 4), but alpha cell cl- increased from 35 +/- 12 to 111 +/- 37 mmol x 1(-1) (n = 3). These effects of ouabain were slow when compared to those exerted by furosemide or Ba2+. The ouabain effects on PDte and PDbl were completely prevented if furosemide was applied first.(ABSTRACT TRUNCATED AT 400 WORDS)

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1984

Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias). III. Effects of stimulation of secretion by cyclic AMP.

Segments of rectal gland tubules (RGT) the spiny dogfish (Squalus acanthias) were perfused in vitro to study the cellular mechanism by which NaCl secretion is stimulated. Transepithelial PD (PDte), transepithelial resistance (Rte), the PD across the basolateral membrane (PDbl), the fractional resistance of the lumen membrane (FR1), and the cellular activities for Cl-, Na+, and K+ (alpha cell x) were measured. In series 1 the effects of stimulation (S) (dbcAMP 10(-4, adenosine 10(-4), and forskolin 10(-6) mol x 1(-1) on these parameters were recorded and compared to nonstimulated state (NS). PDte increased from -1.9 +/- 0.2 mV to -11.0 +/- 0.9 mV (n = 51). PDbl depolarized from -86 +/- 1 to -74 +/- 1.4 mV (n =52), Rte fell from 29 +/- 2.8 to 21 +/- 2 omega cm2 (n = 23), and FR1 fell from 0.96 +/- 0.005 to 0.79 +/- 0.04 (n = 9). alpha cell K+ was constant (123 +/- 13 versus 128 +/- 17 mmol x 1(-1) (n = 6), but alpha cell cl- fell significantly from 48 +/- 4 to 41 +/- 3 mmol x 1(-1) (n = 7). alpha cell Na+ increased from 11 +/- 2.1 to 29.5 +/- 6.6 mmol x 1(-1) (n = 4). In series 2 the conductivity properties were examined by rapid K+, and Cl- concentration steps on the basolateral and luminal cell side respectively in NS and S states. In NS-segments reduction of bath K+ led to a hyperpolarization of PDbl with a mean slope of 28 +/- 1.3 mV/decade (n = 9) (as compared to 19 mV/decade for S-state).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Single channel recordings from basolateral and apical membranes of renal proximal tubules.

A new method is described, which enables the recording of single ionic channels from the basolateral as well as the luminal membrane of renal proximal tubules with the patch-clamp technique. Segments of late proximal tubules of rabbit kidney are cannulated and perfused from one end. The other end is open and freely accessible to a patch pipette. The patch electrode can be moved against lateral cell membranes or can be inserted through the open end into the lumen and brought to contact with the brush-border membrane. Both, in the basolateral as well as in the luminal membrane, giga seals can be achieved. In both membranes, K+ selective channels could be identified.

Animals↗
PubMed1984

Substrate utilization in the isolated perfused cortical thick ascending limb of rabbit nephron.

Isolated segments of cortical thick ascending limbs (cTAL) of rabbit kidney were perfused in vitro and the equivalent short circuit current (Isc) was measured. In a first series all substrates were removed on either side. Isc fell rapidly to 50 +/- 12% after 3 min and to 27 +/- 6% (n = 5) after 10 min. This indicates that in cTAL segments Isc is strictly dependent on the presence of substrates. In series two it was tested what substrates can be utilized by the cTAL segment, and from which epithelial side [bath (b) or lumen (1)] the substrates are taken up. From the 1-side only butyrate (10 mmol X 1(-1) sustained the Isc at 95 +/- 2% (n = 7). All other tested substrates (10 mmol X 1(-1): pyruvate, acetate, beta-OH-butyrate, D-glucose, and L-lactate lead to a marked decline in Isc. From the b-side several substrates (5--10 mmol X 1(-1) sustained the Isc: D-glucose, D-mannose, butyrate, beta-OH-butyrate, acetoacetate, L-lactate, acetate and pyruvate. Other compounds (1--10 mmol X 1(-1): citrate, alpha-ketoglutarate, succinate, glutamate, glutamine, propionate, caprylate and oleate did not sustain Isc. In the third series the mechanism of substrate utilization from the basolateral cell side was studied. It was shown that the Isc is a saturable function of the D-glucose, L-lactate, acetate, pyruvate or beta-OH-butyrate concentration with apparent Km's between 0.05--1.0 mmol X 1(-1). Several known inhibitors of sugar and of anion transport were tested at the bath side: phlorrhizin was without effect. Phloretin (500 mumol X 1(-1) inhibited Isc by 96%, yet its effect was not dependent on the presence of substrates on the b-side since inhibition occurred also if the b-perfusate contained no substrate and Isc was driven by luminal butyrate. Also SITS (5 mmol X 1(-1) exerted only a small inhibitory effect which was not specific since it was also observed with luminal butyrate. alpha-Cyano-m-OH-cinnamate (10 mmol X 1(-1) inhibited the Isc specifically when L-lactate was the bath substrate. Probenecid (1 mmol X 1(-1) had a similar yet less marked inhibitory effect. The D-glucose uptake from the b-side was specifically inhibited by cytochalasin B at 5 X 10(-6) mol X 1(-1). We conclude that the cTAL segment of the rabbit utilizes D-glucose and/or small anions such as pyruvate or L-lactate or acetate to energize salt reabsorption.(ABSTRACT TRUNCATED AT 400 WORDS)

Absorption↗
PubMed1984

Mechanism of NaCl secretion in the rectal gland of spiny dogfish (Squalus acanthias). I. Experiments in isolated in vitro perfused rectal gland tubules.

Rectal gland tubules (RGT) of spiny dogfish were dissected and perfused in vitro. Transepithelial PD (PDte), resistance (Rte), the PD across the basolateral membrane (PDbl) and intracellular chloride and potassium activities (a cell Cl-, a cell K+) were measured. In a first series, 67 RGT segments were perfused with symmetric shark "Ringers" solution. The bath perfusate contained in addition db-cAMP 10(-4), forskolin 10(-6), and adenosine 10(-4) mol X 1(-1). PDte was -11 +/- 1 (n = 67) mV lumen negative, Rte 27 +/- 2 (n = 47) omega cm2, PDbl -75 +/- 0.4 (n = 260) mV. a cell K+ and a cell Cl- were 109 +/- 22 (n = 4) and 38 +/- 4 (n = 36) mmol X 1(-1) respectively. These data indicate that Cl-secretion across the RGT must be an uphill transport process, whereas secretion of Na+ could be driven by the lumen negative PDte. Intracellular K+ is 14 mV above equilibrium with respect to the basolateral membrane PD and Cl- is 23 mV above equilibrium across the apical membrane. In series 2, the conductivity properties of the apical and basolateral membrane as well as that of the paracellular pathway were examined in concentration step experiments. Decrease of the basolateral K+ concentration led to a rapid hyperpolarization of PDbl with a mean slope of 19 mV per decade of K+ concentration change. Addition of 0.5 mmol X 1(-1) Ba2+ to the bath solution lead to a marked depolarization and abolished the response to K+ concentration steps. In the lumen a Cl- concentration downward step led to a depolarization of the lumen membrane; resulting in a mean slope of 18 mV per decade of Cl- concentration change. When dilution potentials were generated across the epithelium, the polarity indicated that the paracellular pathway is cation selective. In series 3 the equivalent short circuit current (Isc = PDte/Rte) was determined as a function of symmetrical changes in Na+ concentration, with Cl- held at 276 mmol X 1(-1), and as a function of symmetrical changes in Cl- concentration, with Na+ held at 278 mmol X 1(-1). Isc was a saturable function of Na+ concentration (Hill coefficient 0.9 +/- 0.1, K1/2 4.4 mmol X 1(-1), n = 7) and also a saturable function of Cl- concentration (Hill coefficient 2.0 +/- 0.1, K1/2 75 mmol X 1(-1), n = 11).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗