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PubMed1977

Active chloride transport in the in vitro opercular skin of a teleost (Fundulus heteroclitus), a gill-like epithelium rich in chloride cells.

1. The opercular epithelium lining the inside of the gill chamber of the killifish, Fundulus heteroclitus, contains Cl(-) cells, identical in fine structure to gill Cl(-) cells, at the high density of 4 x 10(5) cells/cm(2). This epithelium can be isolated, mounted in a Lucite chamber, and its ion transport properties studied with the short-circuit current technique.2. The isolated opercular epithelia of seawater-adapted fish, when bathed on both sides with Ringer and gassed with 100% O(2), displayed a mean short-circuit current of 136.5 +/- 11.1 muA/cm(2), a mean transepithelial potential difference of 18.7 +/- 1.2 mV (blood side positive), and a mean transepithelial d.c. resistance of 173.7 +/- 12.1 Omega.cm(2) (mean +/- S.E. of mean; n = 64).3. The transepithelial potential difference across the opercular epithelia of seawater-adapted fish was dependent on both Na(+) and Cl(-) in the bathing solutions and increased linearly with increasing Cl(-) concentrations with a slope of 28.3 +/- 2.1 mV/tenfold concentration change. The short-circuit current was Na(+) dependent and increased linearly with increasing Cl(-) concentrations with no evidence of saturation kinetics below 142.5 m-equiv/l.4. When the short-circuited epithelia of seawater-adapted fish, bathed on both sides with Ringer, was gassed with 100% O(2) the mean Cl(-) blood side to seawater side flux was 211.7 +/- 27.1 muA/cm(2) and the mean Cl(-) seawater side to blood side flux was 48.9 +/- 10.0 muA/cm(2). This resulted in a net Cl(-) blood side to seawater side flux of 162.8 muA/cm(2) which was not statistically different (P > 0.70) from the mean short-circuit current of 158.6 +/- 16.3 muA/cm(2) for these flux studies. The mean Na(+) blood side to seawater side flux was 32.2 +/- 3.3 muA/cm(2) and the mean Na(+) seawater side to blood side flux was 34.8 +/- 4.1 muA/cm(2), resulting in no significant (P > 0.20) net flux of this cation. Similar results were obtained with short-circuited epithelia of seawater-adapted fish when bathed on both sides with Ringer and gassed with 95% O(2)/5% CO(2).5. Ouabain (10(-5)M), furosemide (10(-3)M), thiocyanate (10(-2)M), adrenaline (10(-6)M), and anoxia (100% N(2)) decreased the short-circuit current 92.7, 85.0, 45.3, 62.6, and 83.3% respectively. Theophylline (10(-4)M) stimulated the short-circuit current 54.9%. Increasing the HCO(3) (-) concentration in the bathing solutions had a stimulatory effect on the short-circuit current and the potential difference across epithelia from seawater-adapted fish.6. The opercular epithelia of freshwater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 94.1 +/- 10.4 muA/cm(2), a mean transepithelial potential difference of 14.8 +/- 1.9 mV (blood side positive), and a mean d.c. resistance of 169.0 +/- 14.0 Omega.cm(2) (mean +/- S.E. of mean; n = 20). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to freshwater side flux of 95.2 +/- 16.1 muA/cm(2) and no significant net flux of Na(+).7. The opercular epithelia of 200% seawater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 33.5 +/- 8.5 muA/cm(2), a mean transepithelial potential difference of 10.5 +/- 2.5 mV (blood side positive), and a mean transepithelial d.c. resistance of 440.7 +/- 62.6 Omega.cm(2) (mean +/- S.E. of mean n = 18). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to seawater side flux of 96.2 +/- 51.5 muA/cm(2) and a net Na(+) blood side to seawater side flux of 65.3 +/- 28.6 muA/cm(2).

Adaptation, Physiological↗
PubMed1979

Non-passive chloride distribution in mammalian heart muscle: micro-electrode measurement of the intracellular chloride activity.

1. Liquid ion-exchanger Cl- -sensitive micro-electrodes were used to make continuous measurements of the intracellular Cl activity, aCli, of quiscent sheep cardiac Purkinje fibres in vitro. 2. aCli was higher than that expected from a passive distribution, (which would have been about 5 mM). It was 3--4 times hiable; EC1 was about 35 mV positive to Em. It was over twice as high in the nominal absence of bicarbonate/CO2 (when the buffer-system was HEPES/O2) but was not always so stable, and ECl was about 20 mV positive to Em. 3. Experiments designed to assess the maximum possible error likely to occur in the measurement of aCli showed that this could not be large and that the estimates of ECl were accurate to within 8 mV. 4. The ability of Cl to move down both concentration and potential gradients was established by demonstrating a loss of aCli in Cl-free solutions and a gain when Em was depolarized positive to ECl in high-K solutions. In both cases, the changes were complete within about 100--160 min. 5. The decline of aCli in Cl-free solutions (glucuronate-substituted) was not significantly affected by changes of [Ca]o from 0 to 12 mM or by the depolarizations of Em of up to 60 mV that sometimes occurred in low or zero [Ca]o. 6. Only 2--3 mM-aClo was sufficient to impede substantially the ready loss of aCli in HEPES-buffered solutions. 7. In high-K solutions (45 mM), Cl appeared to be passively distributed since, at equilibrium, Em and ECl differed by less than 2 mV. 8. In HEPES-buffered Tyrode, ECl of quiescent papillary muscle of the guinea-pig was, on average, 39 mV positive to Em. 9. It is concluded that liquid ion-exchanger Cl- -sensitive micro-electrodes are suitable for studying the Cl regulation of sheep Prukinje fibres, and probably of other cardiac tissues. The measurements of resting aCli are quite accurate when using either HEPES or bicarbonate-buffered Tyrode. The results are discussed in relation to estimates of the apparent membrane Cl permeability under various conditions and the possible existence of an inwardly directed 'Cl pump'.

Animals↗
PubMed1979

Regulation of chloride in quiescent sheep-heart Purkinje fibres studied using intracellular chloride and pH-sensitive micro-electrodes.

1. The intracellular Cl activity, alpha iCl was measured inside quiescent sheep cardiac Purkinje fibres, bathed in normal Tyrode at pH 7.40, buffered with approximately 22 mM-bicarbonate/approximately 5% CO2 + 95% O2. The measurements were made using liquid ion-exchanger Cl-sensitive micro-electrodes. 2. After internal Cl levels had been depleted by prolonged exposure to Cl-free media (glururonate-substituted) when external Cl was restored, there was a rapid re-accumulation of Cl inside the fibres to levels that were much higher than those expected for a passive Cl distribution. Such a process can be conveniently defined as an active inward Cl pump. 3. The inward-pumping was noticeably temperature-sensitive (Q10 approximately 2.6), its rate was reduced about eighteenfold in the nominal absence of external bicarbonate/CO2 and it was substantially inhibited by the drug SITS (4-acetamido-4'-isothiocyanato-stilbene-2,2'-disulphonic acid). 4. The fall of alpha iCl in Cl-free solution was slow and was also equally temperature-sensitive and substantially inhibited by SITS, but was only slightly impaired in the nominal absence of external bicarbonate/CO2. 5. pHi was measured using recessed-tip pH-sensitive micro-electrodes, and in some experiments both pHi and alpha iCl were monitored simultaneously. When alpha iCl slowly declined in Cl-free solution then pHi slowly became alkaline. Upon restoring external Cl, then there was, as usual, a rapid recovery of a high alpha iCl and this was accompanied by a rapid re-acidification of pHi. Both the recovery of alpha iCl and pHi were exponential with virtually the same time constant. 6. Both the slow alkalinization of pHi in Cl-free solution and the rapid re-acidification upon restoring external Cl were substantially inhibited by the drug SITS. 7. When [k]O was raised to 45 mM or more (by removing equivalent amounts of [Na]O), there was a large depolarization of Em and a slow rise of alpha iCl, which was not accompanied by a large change of pHi. The rise of alpha iCl appeared to be unaffected by SITS. 8. It is suggested that a Cl/CHO-3 exchange mechanism can operate reversibly across the membrane of quiescent Purkinje fibres, and that it can account, at least in part, for the high levels of alpha iCl measured in the resting state. It is also concluded that Cl can cross the membrane in other ways, especially in high-K solution possibly by moving passively through conductance channels that are open under these conditions.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1981

Chloride transport and intracellular chloride activity in the presence of theophylline in Amphiuma small intestine.

1. Simultaneous bidirectional tracer fluxes of 22Na and 36Cl were measured under short-circuited conditions in isolated stripped segments of Amphiuma duodenum incubated in media containing Cl- and HCO3-. 2. Theophylline (10 mM) increased the short-circuit current (Isc), eliminated net Cl- absorption and elevated the residual flux by more than 50%. 3. Subsequent addition to acetazolamide lowered the Isc and reduced the residual flux. 4. Using double-barreled Cl- specific micro-electrodes the intracellular activity of Cl- averaged 27.1 mM in the presence of theophylline, consistent with active accumulation of Cl-. 5. Theophylline depolarized the mucosal membrane of villus epithelial cells by an average of 6.9 mV. 6. The findings indicate that the inhibition of Cl- absorption by theophylline does not result from complete inhibition of mucosal Cl- uptake and provide evidence that HCO3- secretion is enhanced by theophylline.

Acetazolamide↗
PubMed1984

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.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1990

Chloride conductance and intracellular chloride accumulation in mouse Peyer's patch enterocytes.

1. Measurements of membrane potential, Cl- conductance and intracellular Cl-, K+, Na+ and H+ activities have been carried out in the follicle-associated epithelium of the mouse Peyer's patch to characterize further the physiological properties of antigen-transporting M cells, enterocytes and intraepithelial lymphocytes. 2. Intraepithelial lymphocytes, identified in random impalements as a second negative jump in membrane potential (Vm), were found to have higher K+ and H+ activities, lower Na+ and Cl- activities and higher negative values for Vm than either of the other two epithelial cell types. Cl- activity in these cells was higher than that predicted from the Nernst equation. 3. M cells identified as having the first negative jump in Vm in impalements involving intraepithelial lymphocytes were unable to accumulate Cl-. They also had a lower Vm than that found in apparently fully differentiated enterocytes. This Vm was partly depolarized at a low Cl- concentration. 4. Apparently fully differentiated enterocytes could be further divided into two populations depending on whether the Vm could or could not be partly depolarized by a low Cl- concentration. The mean Vm and intracellular Cl- activity of Cl(-)-sensitive cells, measured in high Cl- medium, were less than values found for Cl(-)-insensitive enterocytes. Cl- was only accumulated by enterocytes showing no depolarization at low external Cl- concentration. 5. The Vm of mature villus enterocytes was the same as that determined for Cl(-)-insensitive follicle-associated enterocytes. Villus enterocyte Vm was not depolarized at a low Cl- concentration. 6. The present ability to distinguish two apparently large populations of follicle-associated enterocytes having M cell-like or villus enterocyte-like properties is discussed in relation to current theories describing how M cells might be formed. The presence of a Cl- conductance in M cell enterocytes, the inability to accumulate Cl- and the maintenance of a low Vm could aid endocytosis of macromolecules across the apical membrane.

Animals↗
PubMed2004

Slc26a6: a cardiac chloride-hydroxyl exchanger and predominant chloride-bicarbonate exchanger of the mouse heart.

Bicarbonate facilitate more than 50% of pH recovery in the acidotic myocardium, and have roles in cardiac hypertrophy and steady-state pH regulation. To determine which bicarbonate transporters are responsible for this activity, we measured the expression levels of all known HCO3(-)-anion exchange proteins in mouse heart, by quantitative real time RT-PCR. Bicarbonate-anion exchangers are members of either the SLC4A or the SLC26A gene families. In neonatal and adult myocardium, AE1 (Slc4a1), AE2 (Slc4a2), AE3 (Slc4a3) (AE3fl and AE3c variants), Slc26a3 and Slc26a6 were expressed. Adult hearts expressed Slc26a3 and Slc4a1-3 mRNAs at similar levels, while Slc26a6 mRNA was about seven-fold higher than AE3, which was more abundant than any other. Immunohistochemistry revealed that Slc26a6 and AE3 are present in the plasma membrane of ventricular myocytes. Slc26a6 expression levels were higher in ventricle than atrium, whereas AE3 was detected only in ventricle. Cl(-)-HCO(3)(-) and Cl(-)-OH(-) exchange activity of SLC26A6 and AE3 were investigated in transfected HEK293 cells, using intracellular fluorescence measurements of 2',7'-bis (2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), to monitor intracellular pH (pH(i)). Rates of pH(i) change were measured under HCO3(-)-containing (Cl(-)-HCO(3)(-)) or nominally HCO3(-)-free (Cl(-)-OH(-)) conditions. HCO3(-) fluxes were similar for cells expressing AE3fl, SLC26A6 or Slc26a3, suggesting that they have similar transport activity. However, only SLC26A6 and Slc26a3 functioned as Cl(-)-OH(-) exchangers. Activation of alpha-adrenergic receptors, which stimulates protein kinase C, inhibited SLC26A6 Cl(-)-HCO(3)(-) exchange activity. We conclude that Slc26a6 is the predominant Cl(-)-HCO(3)(-) and Cl(-)-OH(-) exchanger of the myocardium and that Slc26a6 is negatively regulated upon alpha-adrenergic stimulation.

Animals↗
PubMed1986

Differential effects of methylmercuric chloride and mercuric chloride on the L-glutamate and potassium evoked release of [3H]dopamine from mouse striatal slices.

The effects of CH3HgCl and HgCl2 on the evoked release of 3H from mouse striatal slices prelabelled with [3H]dopamine have been examined. CH3HgCl (10 microM) was observed to increase the L-glutamate-evoked release of [3H]dopamine, while HgCl2 (10 microM) had no effect. In contrast, CH3HgCl at concentrations up to 100 microM had no effect on the 25 mM K+-stimulated release of [3H]dopamine, whereas HgCl2 (100 microM) significantly reduced the 25 mM K+-stimulated release of [3H]dopamine. Thus CH3HgCl and HgCl2 have differential effects on the L-glutamate- and K+-stimulated release of [3H]dopamine from mouse striatal slices, suggesting that these compounds may have different sites and (or) mechanisms of action in altering neurotransmitter release. It is suggested that CH3HgCl may act predominantly at intracellular sites or at the level of the L-glutamate receptor, whereas the major site of action of HgCl2 may be the voltage-operated calcium channel.

Animals↗