Cl Movement Research Articles

Cyclic AMP alteration of chloride transport into the choroid plexus-cerebrospinal fluid system.

The permeation of 36Cl from blood into choroid plexus (CP) and cerebrospinal fluid (CSF) was studied in adult rats intraventricularly injected with either dibutyryl (db)-cAMP, theophylline with db-cAMP, or forskolin. All 3 treatments significantly enhanced the 15-min distribution (Vd) of 36Cl into CSF, by an average of 17-33%. In contrast, ouabain and acetazolamide (inhibitors of CSF production) reduced 36Cl uptake into CSF by 34% and 13%, respectively. A correlative analysis of the various treatments revealed that the volume of distribution of 36Cl in CSF varied inversely with that in the choroid plexus. This inverse relationship suggests drug effects on Cl movement across the apical (CSF-facing) membrane of CP.

Regulation of apical membrane ion transport in Necturus gallbladder.

Na and Cl movement through the apical membrane of Necturus gallbladder epithelium was investigated using electrophysiological and light microscopic measurements. Changes in membrane potential difference, fractional resistance of the apical membrane, and transepithelial resistance caused by changes in apical bath Cl concentration revealed the presence of a Cl conductance in the apical membrane of control tissues that was apparently not present in the preparations studied by other investigators. This Cl conductance was blocked by bumetanide (10(-5) M) or by the inhibitor of adenosine 3',5'-cyclic monophosphate (cAMP) action, the Rp isomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS; 0.5 mM). Treatment of the tissues with Rp-cAMPS also eliminated bumetanide-sensitive cell swelling in the presence of ouabain and activated an amiloride-sensitive swelling, changes consistent with inhibition of NaCl cotransport and the activation of Na-H and Cl-HCO3 exchange. We conclude that the mode of NaCl entry into Necturus gallbladder epithelial cells is determined by the level of cAMP. When cAMP levels are high, entry occurs by NaCl cotransport; when cAMP levels are low, parallel exchange of Na-H and Cl-HCO3 predominates. These observations explain the previous disagreements about the mode of NaCl entry into Necturus gallbladder epithelial cells.

Effect of Loop Diuretics on Bullfrog Cornea Epithelium

The effect of loop diuretics on Cl transport was studied on an in vitro preparation of the bullfrog cornea. Bumetanide (10(-4) M) or furosemide (10(-3) M) added to the stromal solution decreased Cl transport measured as the short-circuit current (Isc) to values near zero. Concomitantly, transepithelial conductance (gt) decreased, whereas the intracellular potential (Vo) hyperpolarized and the fractional resistance of the apical membrane (fRo) increased. Substitution of SO4 for Cl in the tear-side solution led to prompt changes in Isc, gt, Vo, and fRo, characteristic of appreciable passive Cl movement across the apical membrane before and after inhibition. Epinephrine (10(-4) M) was similarly effective on apical membrane conductance in inhibited tissues as under control conditions, but the effective electromotive force for transepithelial Cl transport was reduced to approximately 25%. Intracellular Cl activity, measured with ion-selective microelectrodes, decreased so much that the difference in electrochemical Cl potential divided by the Faraday constant (delta mu Cl/F) was close to zero after inhibition of Isc by bumetanide. Apical Cl permeability remained essentially unchanged. Accordingly, loop diuretics inhibit Cl transport in the Cl-secreting cornea epithelium by blocking the Na-Cl symport without secondary apical effects, as believed for other Cl-reabsorbing epithelia.

Effect of loop diuretics on bullfrog cornea epithelium.

The effect of loop diuretics on Cl transport was studied on an in vitro preparation of the bullfrog cornea. Bumetanide (10(-4) M) or furosemide (10(-3) M) added to the stromal solution decreased Cl transport measured as the short-circuit current (Isc) to values near zero. Concomitantly, transepithelial conductance (gt) decreased, whereas the intracellular potential (Vo) hyperpolarized and the fractional resistance of the apical membrane (fRo) increased. Substitution of SO4 for Cl in the tear-side solution led to prompt changes in Isc, gt, Vo, and fRo, characteristic of appreciable passive Cl movement across the apical membrane before and after inhibition. Epinephrine (10(-4) M) was similarly effective on apical membrane conductance in inhibited tissues as under control conditions, but the effective electromotive force for transepithelial Cl transport was reduced to approximately 25%. Intracellular Cl activity, measured with ion-selective microelectrodes, decreased so much that the difference in electrochemical Cl potential divided by the Faraday constant (delta mu Cl/F) was close to zero after inhibition of Isc by bumetanide. Apical Cl permeability remained essentially unchanged. Accordingly, loop diuretics inhibit Cl transport in the Cl-secreting cornea epithelium by blocking the Na-Cl symport without secondary apical effects, as believed for other Cl-reabsorbing epithelia.

Potassium secretion by the cortical collecting tubule: effect of C1 gradients and ouabain.

In various epithelia K and Cl transport are molecularly coupled and KCl cotransport is dependent on the Na-K pump. The present study examines 1) the effect of a bath-to-lumen Cl gradient on K secretion during active Na transport and 2) the effect of basolateral ouabain on K secretion and Na absorption in the presence and the absence of a bath-to-lumen Cl gradient. Under symmetrical conditions there was significant K secretion (JK = -24.0 +/- 3.9 pmol.mm-1.min-1) and Cl secretion (JCl = -15.7 +/- 3.7 pmol.mm-1.min-1). Transepithelial voltage (VT) was significantly lumen negative (-25.3 +/- 5.9 mV), and Cl secretion occurred against its electrochemical gradient by a transcellular mechanism. Increasing bath [Cl] did not hyperpolarize VT; in fact there was a tendency for VT to depolarize and K secretion was not stimulated. However, ouabain significantly inhibited active Cl secretion and net Na absorption both in the presence and absence of a bath-to-lumen Cl gradient. Furthermore, ouabain totally inhibited K secretion in the absence of external ion gradients but inhibited K secretion by only 50% in the presence of a bath-to-lumen Cl gradient. This ouabain-insensitive K secretion exhibited a codependence on Cl secretion. Thus K secretion may occur passively, utilizing Cl movement down its electrochemical gradient when active Na transport is inhibited by ouabain. The results are compatible with the presence of a Cl-linked K-secretory process in the rabbit CCT.(ABSTRACT TRUNCATED AT 250 WORDS)

Procaine effects on sodium and chloride transport in frog skin.

Procaine, a tertiary amine, has previously been shown to stimulate reversibly transepithelial Na transport across frog skin after application from the epithelial side. In the present study with intracellular recording from principal, i.e. amiloride-sensitive cells, we demonstrate that the stimulation results from increase in apical membrane Na permeability. A second effect of procaine (10-25 mmol/l) in the outside perfusion solution is a reversible increase of transepithelial conductance which drastically exceeds the predicted response of the transcellular Na pathway. It requires presence of chloride on the epithelial side and depends on the non-ionized molecule of procaine. Abolition of apical membrane Na uptake by amiloride or Na-free mucosal incubation decreases the magnitude but does not prevent the stimulatory effect of procaine. The origin of this gain in conductance from stimulation of a Cl-specific pathway is demonstrated by a highly significant correlation between the increases in electrically determined tissue conductance and partial Cl conductance, obtained from measurements of influx and efflux of Cl-36. Measurements with microelectrodes indicate that the stimulated Cl-specific pathway is distinct from the principal cells. Since procaine activates a conductive pathway with similar response pattern as spontaneously existing Cl conductance, it might be a valuable tool for investigating mode and way of Cl movement across epithelial tissues.

Permeability properties of cell membranes and tight junctions of normal and cystic fibrosis sweat ducts.

The transepithelial permeability properties to Na, K, and Cl in microperfused segments of human eccrine sweat ducts from normal (N) subjects and patients with cystic fibrosis (CF) were examined. Amiloride administered on the luminal surface caused the transepithelial potential (Vt) of normal ducts to depolarize to 0 mV, but in the absence of Cl in the medium or in CF ducts, amiloride caused the Vt to significantly reverse electrical polarity from lumen negative to lumen positive with respect to the serosal bath. The Vt responses to changes in Na concentration in the lumen and K concentration in the bath were similar in CF and N ducts and showed that the basolateral membrane of the duct is K permeable and the apical membrane (in the absence of an anion shunt) is an almost ideal Na electrode. The Vt of N ducts was insensitive to 10-fold changes in luminal K and contraluminal Na solution concentrations. These responses show that in normal ducts, the apical membrane and tight junctions are relatively impermeable to K, and the basal membrane and tight junctions are relatively impermeable to Na. The Vt was highly sensitive to Cl- changes on either surface before or after ouabain inhibition in N ducts, but in every case were insensitive to Cl- changes in CF ducts. By comparison to control ducts the cation selective properties of the CF duct are probably normal, but both cell membranes as well as the tight junctions of the CF duct are relatively impermeable to Cl. The present data are inconclusive as to whether the route of Cl movement across the N duct epithelium is trans- or paracellular.

Effects of inhibitors of Cl conductance on Cl self-exchange in rabbit cortical collecting tubule.

Electroneutral vs. conductive pathways of Cl transport were examined by measuring transepithelial conductance (GT) and the lumen-to-bath 36Cl rate coefficient (KCl). Experimental conditions minimized both Cl-HCO3 exchange [HCO3/CO2-free, N-2-hydroxyethylpiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered solutions] and the electrical driving force for paracellular Cl diffusion (amiloride in the perfusate, transepithelial voltage near zero). Two agents known to inhibit Cl conductances in other epithelia, anthracene-9-carboxylate (9AC, 1 mM) and diphenylamine carboxylate (DPC, 0.1-0.5 mM) reversibly reduced GT and KCl when added to the bath. Both reduced KCl to values consistent with paracellular diffusion. Bath DPC had no effect on GT in the presence of 4 mM lumen Ba2+, suggesting that the DPC-sensitive conductance is in series with an apical K conductance, i.e., resides on the basolateral membrane. Lumen DPC also reduced GT and KCl, but was less potent than bath DPC. Because the lumen DPC effect on GT was also blocked by lumen Ba2+, lumen DPC probably inhibits a basolateral Cl conductance. K removal and ouabain (0.5 mM) had no effect on KCl, suggesting that Cl tracer movement is not predominantly through the principal cell. We assume that these agents are inhibiting Cl conductive pathways and propose a model in which transcellular Cl movement through the intercalated cell occurs via an apical electroneutral entry step in series with a basolateral conductive pathway.

Active transport and exchange diffusion of Cl across the isolated skin of Rana pipiens.

Transepithelial Cl influx and efflux were measured in pairs of frog skin (Rana pipiens) matched according to short-circuit current, tissue conductance, and transepithelial potential (TEP). The skins were bathed symmetrically in NaCl Ringer and voltage clamped at TEP values ranging from -60 to +60 mV. At 0 TEP, Cl influx and net inward Cl movement (in neq X h-1 X cm-2) were, respectively, 961 +/- 116 and 463 +/- 68 in NaCl Ringer, 509 +/- 52 and 202 +/- 53 in amiloride-treated skins, 4,168 +/- 777 and 1,444 +/- 447 in theophylline-treated skins, and 587 +/- 38 and 97 +/- 44 in Na-free Ringer. A correlation was discovered between short-circuit current and Cl fluxes corresponding to a 2:6:1 relationship between changes in active Na transport and active Cl transport. Deviations from the predicted Cl flux ratio indicate the presence of exchange diffusion in the range of spontaneously occurring TEPs, in contrast to observations on R. temporaria and R. esculenta. The experiments indicate that a substantial portion of transepithelial Cl movement proceeds transcellularly 1) via active Cl transport that is Na dependent, amiloride sensitive, stimulated by theophylline, and apparently correlated with active Na transport, and 2) by means of exchange diffusion that not only occurs under short-circuit conditions but also at positive TEPs. It is possible to explain both the exchange diffusion and the properties of active Cl transport by a Cl-HCO3 exchange system at the apical side of the transporting cell that interacts with a Na-H exchange mechanism, a notion consistent with the recent observation of an amiloride-induced decrease in intracellular pH.

Modelling water flow through undisturbed soil cores using a transfer function model derived from 3HOH and Cl transport

SUMMARYLarge undisturbed soil cores (20 cm diam. × 25–30 cm long) were irrigated at rates of 0.5–4 cm h−1 with 0.005 M CaCl2 solution labelled with 3HOH. The cores were used at varying initial water contents and flow in all cases was unsaturated. Breakthrough curves for Cl and 3HOH were markedly asymmetric and unlike those reported for columns of packed aggregates. The data could be satisfactorily described using a density distribution function of the logarithm of cumulative drainage D. The mean and standard deviation of In D were estimated by a curve‐fitting procedure from Cl and 3HOH effluent concentrations in each core. The mean pore water velocity and fraction of the soil water that participated in solute transport (the mobile volume) were also calculated.The apparent velocity of Cl movement was always greater than that of 3HOH which suggested that the mobile volume involved in convective and diffusive transport of Cl was less than that for 3HOH. We suggest that Cl and 3HOH diffused at different rates out of flowing water films in a relatively few large conducting channels into essentially immobile water within the surrounding soil matrix. The difference in mobile volume for Cl and 3HOH was used to calculate the perimeter of voids in any horizontal cross‐section of the soil through which water flowed, assuming a planar interface between the mobile and immobile water.

The role of chloride-bicarbonate exchange in the regulation of intracellular chloride in guinea-pig vas deferens.

The Cl-depleted smooth muscle cells of guinea-pig vas deferens rapidly restore their intracellular Cl activity ( aiCl ) to a level 5 times higher than that predicted by a passive distribution when Cl- ions are readmitted to the extracellular solution. Cl reaccumulation, measured using Cl-sensitive micro-electrodes and the uptake of 36Cl, was slowed about 3-fold by the nominal absence of CO2 and HCO3 and about 10-fold by the presence of the anion exchange inhibitor DIDS (4-4'-diisothiocyanostilbene-2,2'-disulphonic acid). However, the usual level of intracellular Cl was eventually attained and neither condition reduced intracellular Cl in normal tissues. The loss of intracellular Cl that occurs when Cl- ions are removed from the extracellular solution was slowed about 3-fold by the nominal absence of CO2 and HCO3 and was accelerated by their readdition. DIDS slowed the fall in aiCl about 10-fold and reduced 36Cl efflux. Intracellular pH (pHi), measured using pH-sensitive micro-electrodes, increased by a mean of 0.73 units when Cl was removed from the superfusing solution in the presence of CO2 and HCO3, and rapidly decreased when Cl was readmitted. These changes are equivalent to an intracellular accumulation and loss of HCO3- ions respectively. The net transmembrane movement of HCO3- ions which would have caused these changes in pHi was calculated using the measured intracellular buffering power ( Aickin , 1984). 25% fewer HCO3- ions than Cl- ions were accumulated and lost and the HCO3 movement was completed 2-3 times faster than the simultaneous Cl movement under the same conditions. The changes in pHi induced by alteration of extracellular Cl were reduced by the nominal absence of CO2 and HCO3 and abolished by the presence of DIDS. The acidification recorded on readmission of Cl in the nominal absence of CO2 and HCO3 was compatible with a metabolic production of about 0.1% CO2. We conclude that Cl-HCO3 exchange plays a major role in the regulation of intracellular Cl. The exchange carrier is reversible, is completely inhibited by DIDS, and accounts for about 75% of the net Cl movement that occurs when Cl is removed from or readmitted to the extracellular solution. The mechanism which is responsible for the remaining Cl movement remains to be elucidated.

Intracellular chloride activities in the isolated perfused shark rectal gland.

The isolated, perfused shark rectal gland secretes Cl when stimulated with adenosine 3',5'-cyclic monophosphate (cAMP). To investigate the mechanism of secretion, we used Cl-selective and conventional (KCl-filled) microelectrodes to measure the intracellular Cl activity (aClc). Under nonsecreting conditions, the electrical potential difference across the basolateral membrane (psi b) was -78 m V and aClc was 57 mM, a value seven times greater than predicted for electrochemical equilibrium across the basolateral membrane. When theophylline and 8-bromo-cAMP were added to the perfusate, the transglandular electrical potential difference doubled and the rate of fluid secretion increased 20-fold; however, neither psi b nor aClc changed. During both nonsecreting and secreting conditions the intracellular accumulation of Cl results in an electrochemical potential difference favoring Cl exit across the apical cell membrane. The constancy of aClc despite the variation in secretion rate suggests that stimulation is associated with an equivalent enhancement of net Cl movement across both the apical and basolateral membranes. When stimulated glands were perfused with Na-free (choline) Ringer, secretion was abolished and aClc fell toward the value predicted for electrochemical equilibrium. These findings suggest that the "uphill" step in Cl secretion lies at the basolateral membrane, where cellular Cl accumulation probably involves secondary active transport; i.e., Cl entry is driven by an inwardly directed electrochemical potential difference for Na.

Towards an estimate of chloride permeability in the smooth muscle of guinea-pig vas deferens.

Cl movements across the cell membranes of smooth muscle from the guinea-pig vas deferens were measured using Cl-sensitive micro-electrodes and 36Cl fluxes. The rate constants for the loss of Cl ions measured by both methods under a variety of conditions were used to calculate the apparent Cl permeability (PCl). If it is assumed that the initial rate of decline of the intracellular Cl activity (aiCl) on removal of extracellular Cl (Clo) represents net transmembrane Cl movement, the apparent PCl was 3-6 X 10(-8) cm s-1. This value is in good agreement with those calculated from the rate constant of 36Cl efflux into both normal Krebs solution (steady-state) and Cl-free solution. Such a value for PCl predicts a large depolarization on removal of Clo, but only a minimal change was recorded. It also predicts that changes in membrane potential (Em) would affect aiCl; furthermore that removal of Clo would increase membrane resistance and thus the hyperpolarization observed on reactivation of the electrogenic Na pump. Neither of these was observed. The PCl/PK ratio obtained from changes in Em on rapid changes in Clo and Ko gives a value for PCl which is an order of magnitude lower: 4 X 10(-9) cm s-1, using Casteels' (1969 b) value for PK. These observations can be reconciled by a substantial proportion of the measured Cl movements being carrier-mediated. The presence of the stilbene derivative DIDS greatly slowed both the steady-state efflux and uptake of 36Cl, as has previously been shown for the loss and reaccumulation of Cl ions on removal and replacement of Clo. PCl calculated in the presence of DIDS was about 5 X 10(-9) cm s-1. The nominal absence of CO2 and HCO3, which slows the reaccumulation and loss of Cl, had no effect on the steady-state fluxes. This indicates that the carrier operates in the self-exchange mode in the steady state.

A possible role of linked Na and Cl movement in active Cl uptake in smooth muscle.

Smooth muscles actively accumulate Cl. Abolition of the transmembrane Na gradient has been shown to lead to a passive distribution of Cl. This suggested to us that Na and Cl may move together across the smooth muscle cell membrane, Cl accumulation resulting due to [Na]i being less than [Na]o. In favour of this view are the findings that Cl uptake is reduced in Na-free medium, Na uptake is reduced in Cl-free medium, reducing [Cl]i reduces Na efflux, and increasing [Na]i increases Cl efflux.

Sodium-coupled chloride transport by epithelial tissues

There is compelling evidence that active Cl absorption by a variety of epithelia, widely distributed throughout the animal kingdom, is the result of an electrically neutral Na-coupled transport process at the luminal membrane and that the energy for transcellular Cl movement is derived from the Na gradient across that barrier. These co-transport processes are found predominantly in "leaky" or "moderately leaky" epithelia and permit these tissues to absorb Na and Cl with high degrees of efficacy. In addition, there is a growing body of evidence that cyclic AMP and Ca-induced electrogenic Cl secretion by a wide variety of epithelia may involve electrically neutral, Na-coupled Cl entry across the contraluminal membrane and that the energy for these secretory processes is derived from the Na-gradient across that barrier. A model for electrogenic Cl secretion that accounts for the available data is presented.

Nitrate‐Nitrogen and Chloride Movement Through Undisturbed Field Soil

AbstractResults are presented from a field study conducted to determine whether large pores represent a major pathway for NO3‐N and Cl movement through undisturbed soil. A solution containing 410 ppm NO3‐N and Cl as KNO3 and KCl was added to three experimental field plots enclosed by wooden barriers to prevent runoff. Initial and final soil samples were taken at various profile depths for ion analyses. Most of the NO3‐N and Cl added in solution moved vertically with the water through the profile. Ion movement was influenced by large soil pores between structural units. A fourth field plot was designed to compare field‐measured NO3‐N and Cl concentrations with theoretical calculations, using time‐dependent water flow velocity and dispersion equations. Soil solution samples were taken for ion analyses. Due to the incomplete mixing of water and ions with all soil pores, theoretical equations did not completely explain the field‐measured NO3‐N and Cl distributions.

Catecholamine-induced changes in ion transport in short-circuited frog skin and the effect of beta-blockade.

1. A method for measuring bidirectional Cl fluxes has been used to estimate net Cl movements in short-circuited frog skin and to compare these with the short-circuit current (Isc) and Na fluxes. 2. In some experiments bidirectional fluxes of both Na and Cl were measured simultaneously. It was found that the algebraic sum of the net fluxes of these two ions did not differ significantly from the values of Isc, either in untreated or catecholamine-treated skins, except for the half-hour period immediately after catecholamine addition. 3. The net effluxes of Cl produced by noradrenaline (1-6 X 10(-5)M), isoprenaline (8 X 10(-7)M) and adrenaline (6 and 15 X 10(-6)M) were of similar magnitude for each catecholamine. The magnitude of the Cl response measured as a flux ratio was related to a certain extent to the precatecholamine Cl conductance. 4. The net Na influx was increased by isoprenaline and reduced by noradrenaline. 5. Addition of the beta-adrenergic blocking agent oxprenolol (4-5 X 10(-5)M) to skins stimulated by catecholamine resulted in the disappearance of the net Cl movement and fall in skin conductance and Isc. This fall was similar in magnitude to, and correlated with the mean rise in Isc produced by isoprenaline, but of significantly greater magnitude in the case of noradrenaline. 6. The changes in Na influx were strongly associated with the changes in Isc following catecholamine addition. Similarly, the changes in Na efflux and Cl efflux were correlated, suggesting the Na fluxes to be dissociated, influx and efflux changes perhaps taking place at different loci. 7. Acetazolamide (1-2 X 10(-4)M), added either before or during the noradrenaline stimulation, had no effect on the Cl efflux response. 8. The tissue exchange of Cl from the outside bathing medium after 4 hr was greater in catecholamine-stimulated skins than in those in which the response had been blocked by oxprenolol. 9. These findings were taken to support a model entailing a neutral NaCl pump resident in the mucous glands and an epithelial Na pump enhanced by beta- and inhibited by alpha-adrenergic stimulation.

Electrochemical Gradients and K+ and Cl− Fluxes in Excised Corn Roots

The compartmental analysis method was used to estimate the K(+) and Cl(-) fluxes for cells of excised roots of Zea mays L. cv. Golden Bantam. When the measured fluxes are compared to those calculated with the Ussing-Teorell flux-ratio equation, an active inward transport of Cl(-) across the plasmalemma is indicated; the plasmalemma K(+) fluxes are not far different from those predicted for passive diffusion, although an active inward transport cannot be precluded. Whether fluxes across the tonoplast are active or passive depends upon the vacuolar potential which is unknown. Assuming no electropotential gradient, the tracer flux ratios are fairly close to those predicted for passive movement. However, if the vacuole is positive by about 10 millivolts relative to the cytoplasm, the data suggest active inward transport for K(+) and outward transport for Cl(-).Fluxes to the xylem exudate were found to be more accurately estimated from the specific radioactivity of the cytoplasm (symplasm) than from the external solution specific radioactivity. The electrochemical gradients for K(+) and Cl(-) between the xylem vessels and the surrounding stelar parenchyma indicate active K(+) and passive Cl(-) movement into the vessels. The data are interpreted as being in accord with radial transport through the symplast into living vessels.

Actions of external hypertonic urea, ADH, and theophylline on transcellular and extracellular solute permeabilities in frog skin.

Increases in transepithelial solute permeability were elicited in the frog skin with external hypertonic urea, theophylline, and vasopressin (ADH). In external hypertonic urea, which is known to increase the permeability of the extracellular (paracellular) pathway, the unidirectional transepithelial fluxes of Na (passive), K, Cl, and urea increased substantially while preserving a linear relationship to each other. The same linear relationship was also observed for the passive Na and urea fluxes in regular Ringer and under stimulation with ADH or 10 mM theophylline, indicating that their permeation pathway was extracellular. A linear relationship between Cl and urea fluxes could be demonstrated if the skins were separated according to their open circuit potentials; parallel lines were obtained with increasing intercepts on the Cl axis as the open circuit potential decreased. The slopes of the Cl vs. urea lines were not different from that obtained in external hypertonic urea, indicating that this relationship described the extracellular movement of Cl. The intercept on the ordinate was interpreted as the contribution from the transcellular Cl movement. In the presence of 0.5 mM theophylline or 10 mU/ml of ADH, mainly the transcellular movement of Cl increased, whereas 10 mM theophylline caused increases in both transcellular and extracellular Cl fluxes. These and other data were interpreted in terms of a possible intracellular control of the theophylline-induced increase in extracellular fluxes. The changes in passive solute permeability were shown to be independent of active transport. The responses of the active transport system, the transcellular and paracellular pathways to theophylline and ADH could be explained in terms of the different resulting concentrations of cyclic 3'-5'-AMP produced by each of these substances in the tissue.

Effect of pH and Auxin on Chloride Uptake into Avena Coleoptile Cells

The effect of pH on (36)Cl(-) movement into coleoptile cells (Avena sativa L. cv. Garry) was investigated and compared with effects of indoleacetic acid. (36)Cl(-) uptake, but not efflux, is stimulated when coleoptile sections are placed in media adjusted to pH levels from 5 to 3 after a preincubation period at pH 6.5. The enhancement is seen within 2 minutes, is not correlated with growth, and is completely erased by respiratory inhibitors. In comparison to the acid-induced stimulation, the stimulatory effect of indoleacetic acid on (36)Cl(-) uptake is also not accompanied by accelerated efflux, and indoleacetic acid does not further stimulate (36)Cl(-) uptake into 1-millimeter sections beyond that seen at pH 3.5 without auxin.