Biomedical subjects

D Restrepo

Publications and source records attributed to D Restrepo.

At least 19 recordsLinked to original sources

PubMed1997

Selectivity and response characteristics of human olfactory neurons.

Transduction mechanisms were investigated in human olfactory neurons by determining characteristics of odorant-induced changes in intracellular calcium concentration ([Ca2+]i). Olfactory neurons were freshly isolated from nasal biopsies, allowed to attach to coverslips, and loaded with the calcium-sensitive indicator fura-2. Changes in [Ca2+]i were studied in response to exposure to individual odors, or odorant mixtures composed to distinguish between transduction pathways mediated by adenosine 3'5'-monophosphate (cAMP; mix A) or inositol 1,4,5-trisphosphate (InsP3; mix B). Overall, 52% of biopsies produced one or more odorant-responsive olfactory neurons, whereas 24% of all olfactory neurons tested responded to odorant exposure with a change in [Ca2+]i. As in olfactory neurons from other species, the data suggest that odorant exposure elicited calcium influx via second-messenger pathways involving cAMP or InsP3. Unlike olfactory neurons from other species that have been tested, some human olfactory neurons responded to odorants with decreases in [Ca2+]i. Also in contrast with olfactory neurons from other species, human olfactory neurons were better able to discriminate between odorant mixtures in that no neuron responded to more than one type of odor or mixture. These results suggest the presence of a previously unreported type of olfactory transduction mechanism, and raise the possibility that coding of odor qualities in humans may be accomplished to some degree differently than in other vertebrates, with the olfactory neuron itself making a greater contribution to the discrimination process.

Adolescent↗

PubMed1996

Second messenger signaling in olfactory transduction.

Olfactory receptor neurons respond to odorants with G-protein mediated increases in the concentration of cyclic adenosine 3',5'-monophosphate (cAMP) and/or inositol 1,4,5-trisphospahte (InsP3). These two second messengers directly regulate opening of cAMP- and InsP3-regulated conductances localized to the apical transduction compartments of the cell (cilia and olfactory knob). In the presence of physiological concentrations of extracellular Ca2+, these second messenger regulated conductances mediate influx of Ca2+ into the olfactory neuron resulting in large, localized increases in intracellular Ca2+ ([Ca2+]i). A significant advance in our understanding of the molecular mechanisms of olfaction is the recent realization that this increase in [Ca2+]i plays an important role as a "third messenger" in olfactory transduction. Second messenger dependent increases in [Ca2+]i cause opening of ciliary Ca(2+)-activated Cl-, cation and/ or K+ channels that can carry a large percentage of the generator current, thus amplifying the signal substantially. As a result of this sequence of events, the generator potential in olfactory neurons can be depolarizing, leading to excitation of the neuron, or hyperpolarizing, leading to suppression of basal action potential firing rate. This dual effect of odorants on olfactory neurons may play an important role in quality coding and in the ability to detect low concentrations of odorants, particularly in complex mixtures.

Animals↗

PubMed1996

Single taste stimuli elicit either increases or decreases in intracellular calcium in isolated catfish taste cells.

Taste cells are specialized epithelial cells that respond to stimulation with release of neurotransmitters onto afferent nerves that innervate taste buds. In analogy to neurotransmitter release in other cells, it is expected that neurotransmitter release in taste cells is dependent on an increase in intracellular Ca2+ ([Ca2+]i). We have studied changes in [Ca2+]i elicited by the taste stimuli L- and D-arginine in isolated taste cells from the channel catfish (Ictalurus punctatus). In a sample of 119 cells, we found 15 cells responding to L-arginine, and 12 cells responding to D-arginine with an increase in [Ca2+]i. The response to L-arginine was inhibited by equimolar D-arginine in cells where D-arginine alone did not cause a change in [Ca2+]i, which is consistent with mediation of this response by a previously characterized L-arginine-gated nonspecific cation channel antagonized by D-arginine [31]. However, we also found that these taste stimuli elicited decreases in [Ca2+]i in substantial number of cells (6 for L-Arg, and 2 for D-Arg, n = 119). These observations suggest that stimulation of taste cells with sapid stimuli may result in simultaneous excitation and inhibition of different taste cells within the taste bud, which could be involved in local processing of the taste signal.

Animals↗

PubMed1996

G alpha 9/G alpha 11: immunolocalization in the olfactory epithelium of the rat (Rattus rattus) and the channel catfish (Ictalurus punctatus).

The immunohistochemical localization of G alpha 9/G alpha 11 was studied in the olfactory and respiratory epithelium of two representative vertebrates, the rat and the channel catfish. Localization in the rat was found at the apical surface of cells in the epithelium and within nerve tracts in the lamina propria. Immunostaining of neuronal cilia and supporting cell microvilli was confirmed by electron microscopy. Immunoreactivity on the ipsilateral neuroepithelium was abolished five weeks following unilateral bulbectomy. An emergence of patchy immunoreactivity was found, however, after fifteen weeks. In catfish, G alpha 9/G alpha 11 antigenicity was found at the apical surface of cells within the olfactory epithelium, at supranuclear regions within some cell bodies and in basal nerve tracts of the olfactory rosette. Immunoreactivity was removed with unilateral bulbectomy. Specific labelling in both rat and catfish was eliminated by preincubation of the G alpha 9/G alpha 11 antibodies with the cognate peptide. Proteins were extracted from olfactory tissues of both species and solubilized. Using western blotting, bands corresponding in apparent molecular weight to a 38,000 mol. wt protein were found. These data demonstrate the presence of G alpha 9/G alpha 11 in the olfactory tissues of these vertebrates and suggest a role in olfaction for this class of G-protein.

Animals↗

PubMed1996

Induction of differentiation of human olfactory neuroblastoma cells into odorant-responsive cells.

Olfactory neuroblastoma is a rare malignancy of the olfactory mucosa that may be derived from the olfactory epithelium. To characterize this tumor, we cultured olfactory neuroblastoma cells in the presence or absence of growth factors (transforming growth factor alpha and basic fibroblast growth factor) known to affect olfactory tissue and assessed their responsiveness to known odorants by measuring changes in intracellular calcium. Untreated cells did not respond to odorants. Basic fibroblast growth factor treatment had cytotoxic effects, and treated cells did not respond to odorants. Transforming growth factor alpha treatment resulted in the induction of odor responsiveness in these cells. Cells responded to odorants at 100 nM to 100 microM concentrations and responded with both increases and decreases in intracellular calcium. Increases in intracellular calcium were mediated by a calcium influx and were reversibly blocked by compounds known to inhibit second messenger pathways in olfactory receptor neurons. The calcium responses of the olfactory neuroblastoma cells were thus specific to the odorants and similar to those found in olfactory receptor neurons. The results support the notion that olfactory neuroblastoma cells may be of olfactory origin and thus they can be used as a model cell line to study human olfaction.

Calcium↗

PubMed1996

Measurement of membrane potential and [Ca2+]i in cell ensembles: application to the study of glutamate taste in mice.

We have studied the spectral properties of the voltage-sensitive dye, 1-(3-sulfonatopropyl)-4-[beta [2-(di-n-octylamino)-6-naphtyl]vinyl] pyridinium betaine (di-8-ANEPPS), and the Ca(2+)-sensitive dye, fura-2, in azolectin liposomes and in isolated taste buds from mouse. We find that the fluorescence excitation spectra of di-8-ANEPPS and fura-2 are largely nonoverlapping, allowing alternate ratio measurements of membrane potential and intracellular calcium ([Ca2+]i). There is a small spillover of di-8-ANEPPS fluorescence at the excitation wavelengths used for fura-2 (340 and 360 nm). However, voltage-induced changes in the fluorescence of di-8-ANEPPS, excited at the fura-2 wavelengths, are small. In addition, di-8-ANEPPS fluorescence is localized to the membrane, whereas fura-2 fluorescence is distributed throughout the cytoplasm. Because of this, the effect of spillover of di-8-ANEPPS fluorescence in the [Ca2+]i estimate is < 1%, under the appropriate conditions. We have applied this method to study of the responses of multiple taste cells within isolated taste buds. We show that membrane potential and [Ca2+]i can be measured alternately in isolated taste buds from mouse. Stimulation with glutamate and glutamate analogs indicates that taste cells express both metabotropic and ionotropic receptors. The data suggest that the receptors responding to 2-amino-4-phosphonobutyrate (L-AP4), presumably metabotropic L-glutamate receptors, do not mediate excitatory glutamate taste responses.

Animals↗

PubMed1995

InsP3-gated ion channels in rat olfactory cilia membrane.

InsP3-gated channels present in isolated rat olfactory cilia membranes were studied by recording current fluctuations in cilia membranes fused onto phospholipid bilayers formed at the tip of a patch pipette. We found that InsP3 (1.25 to 30 microM) induced current fluctuations in 18 of 157 otherwise silent bilayers. The ion channels opened by InsP3 could be classified into two groups that differed in terms of conductance and kinetics. One channel, which had a conductance of 37 pS, displayed two current levels, and the larger single channel currents were associated with longer open dwell times. The other channel displayed a larger conductance (103-184 pS). Both types of channels displayed reversal potentials near zero millivolts, consistent with nonspecific cation channels. These experiments suggest that mammalian olfactory neurons possess two types of ciliary InsP3-gated channels.

Animals↗

PubMed1995

Functionally mature olfactory neurons from two anosmic patients with Kallmann syndrome.

Patients with Kallmann syndrome (KS) exhibit hypogonadotropic hypogonadism and anosmia [Kallmann et al., Am. J. Mental Def., 48 (1944) 203-236] secondary to failure of gonadotropin-releasing hormone (GnRH)-producing neurons to migrate from the olfactory placode to the brain, and to agenesis of the olfactory bulbs. It has been hypothesized that olfactory neurons (ON) from individuals with KS are immature partly on the basis of studies in animals showing that lack of synaptic connection of ON with the olfactory bulb results in expression of immature ON [Schwob et al., J. Neurosci., 12 (1979) 880-883]. To test this assumption, we obtained olfactory tissue samples from two males diagnosed with KS on the basis of medical history and MRI studies. Both patients were anosmic. The functioning of cells isolated from biopsies taken from the upper middle turbinate and septum was studied by measuring changes in intracellular Ca2+ concentration ([Cai]) using dual excitation fluorescence microscopy. Biopsies from both patients yielded cells that morphologically appeared to be ON. Seven of 16 cells that morphologically resembled ON responded with a change in [Cai] upon stimulation with an odorant mixture. These studies show that at least some ON in KS individuals are functionally mature and suggest that complete development of the olfactory bulbs is not required for differentiation of mature human ON.

Adolescent↗

PubMed1995

NADPH diaphorase staining suggests localization of nitric oxide synthase within mature vertebrate olfactory neurons.

Nitric oxide, a simple gas which serves as a neurotransmitter in the CNS, has been proposed to serve as an interneuronal second messenger in olfactory transduction. However, the role of nitric oxide in olfaction has been questioned by experiments in which nitric oxide synthase, the enzyme that generates nitric oxide, could not be localized to the olfactory epithelium. We have localized nitric oxide synthase to the olfactory neurons in adult rat and catfish olfactory epithelia using a modified nicotinamide adenine dinucleotide phosphate diaphorase technique. In the rat, staining was also found in cells with morphology reminiscent of microvillar olfactory cells. In contrast, the respiratory epithelium and the sustentacular cells in the olfactory epithelium displayed no staining. The nicotinamide adenine dinucleotide phosphate diaphorase reaction, which has been shown to co-localize with immunohistochemical staining for nitric oxide synthase in the brain, was stimulated by addition of the nitric oxide synthase substrate L-arginine, and was inhibited by the nitric oxide synthase inhibitor L-NG-nitro arginine, indicating that staining was specific for nitric oxide synthase. Unilateral bulbectomy, which causes degeneration of mature olfactory neurons on the bulbectomized size, markedly reduced nicotinamide adenine dinucleotide phosphate diaphorase staining. These observations were substantiated by biochemical assays for nitric oxide synthase by monitoring the production of [3H]-L-citrulline from [3H]-L-arginine. This is the first demonstration of specific NADPH diaphorase staining of mature olfactory neurons in rat and catfish olfactory epithelial suggesting the presence of nitric oxide synthase in these cells. Our histological and biochemical findings, in conjunction with data from other research, are supportive of a role for nitric oxide synthase in olfactory function.

Amino Acid Oxidoreductases↗

PubMed1995

InsP3 causes an increase in apical [Ca2+]i by activating two distinct current components in vertebrate olfactory receptor cells.

1. Effects of inositol-1,4,5-trisphosphate (InsP3) applied through a patch pipette to Xenopus laevis olfactory receptor cells (ORCs) were studied using the patch-clamp technique in conjunction with calcium imaging with fura-2. 2. InsP3 activated, first, a novel voltage-independent Ca2+ current (ICa) and, second, a nonselective cation current (Icat). 3. The activation of these currents occurred at different intracellular calcium concentrations, and the activation of either current led to a marked increase of [Ca2+]i in the dendritic knob. 4. The results suggest that InsP3 might act as a second messenger in vertebrate olfactory receptor cells by activating, through different mechanisms, a plasma membrane Ca2+ conductance (ICa) and a nonselective cation conductance (Icat).

Animals↗

PubMed1994

Control of intracellular pH during regulatory volume decrease in HL-60 cells.

Intracellular pH (pHi) homeostasis was investigated in human promyelocytic leukemic HL-60 cells as they undergo regulatory volume decrease (RVD) in hypotonic media to determine how well pHi is regulated and which transport systems are involved. Cells suspended in hypotonic (50-60% of isotonic) media undergo a small (< 0.2 pH units), but significant (P < 0.05), intracellular acidification within 5 min. However, after 30 min of RVD, pHi is not significantly different from the initial pHi in 20 mM HCO3- medium and is significantly higher in HCO3(-)-free medium. Experiments performed in media with or without 150 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid and HCO3- demonstrate that the anion exchanger (AE) mediates a net Cl- influx, with compensating HCO3- efflux, during RVD. To determine which transport systems are involved in counteracting this tendency toward acidification, we measured transport rates and examined the effect of transport system inhibitors on pHi. We found that inhibition of Na+/H+ exchange (NHE) with 12.5 microM ethylisoproplamiloride (EIPA) causes pHi to fall significantly by the end of 30 min of RVD. As assessed by EIPA-sensitive 22Na+ uptake measurements, NHE, largely dormant under resting isotonic conditions, becomes significantly activated by the end of 30 min of RVD, despite recovery of pHi and cell volume to near-normal levels. Thus a shift in the normal pHi dependence and/or volume dependence of NHE activity must occur during RVD under hypotonic conditions. In contrast, H(+)-monocarboxylate cotransport appears to play only a supportive role in pH regulation during RVD, as indicated by lack of stimulation of [14C]lactate efflux during RVD.

Anions↗

PubMed1994

Inositol 1,4,5-trisphosphate-gated conductance in isolated rat olfactory neurons.

1. The effect of intracellular application of inositol 1,4,5-trisphosphate (IP3) from the patch pipette was analyzed in isolated rat olfactory neurons under whole-cell patch clamp. 2. Intracellular dialysis of 10 microM 1,4,5-IP3 in K(+)-internal solution induced a sustained depolarization of 35.8 +/- 10.5 (SD) mV (n = 16). The IP3-induced response was observed in 75% of the cells dialyzed with IP3 but not when 10 microM ruthenium red was also included in the pipette solution (4 cells). Lower concentrations (50-100 nM) of 2,4,5-IP3 induced similar responses to those produced by 1,4,5-IP3 in five of eight olfactory neurons. 3. Steady-state I-V relationships of IP3-gated currents with K(+)-internal solution were classified into two types: outwardly rectifying and N-shaped. In Cs(+)-internal solution outwardly rectifying and linear patterns were observed. 4. The IP3-induced currents were inhibited by external Cd2+ (1 mM). The reversal potentials of the Cd(2+)-inhibitable currents were -16.1 mV (n = 2) and -29.0 +/- 7.1 mV (n = 3) for the outwardly rectifying and N-shaped types, respectively, in K(+)-internal solution. The reversal potential was -5.9 +/- 6.8 mV (n = 5) in the Cs(+)-internal solution. 6. In contrast, the Ca(2+)-ionophore, ionomycin (5 microM) hyperpolarized the olfactory neurons and greatly potentiated the outward currents at positive holding membrane potential. 7. The data suggest that IP3 can depolarize rat olfactory neurons without mediation by intracellular Ca2+.

Animals↗

PubMed1993

Human olfactory neurons respond to odor stimuli with an increase in cytoplasmic Ca2+.

The sense of smell allows terrestrial animals to collect information about the chemical nature of their environment through the detection of airborne molecules. In humans smell is believed to play an important role in protecting the organism from environmental hazards such as fire, gas leaks and spoiled food, in determining the flavor of foods, and perhaps in infant-parent bonding. In addition, the study of human olfaction is relevant to a number of medical problems that result in olfactory dysfunction, which can affect nutritional state, and to the study of the etiology of neurodegenerative diseases which manifest themselves in the olfactory epithelium. Although much is known about behavioral aspects of human olfaction, little is understood about the underlying cellular mechanisms in humans. Here we report that viable human olfactory neurons (HON) can be isolated from olfactory tissue biopsies, and we find that HON respond to odorants with an increase in intracellular calcium concentration ([Cai]).

Biopsy↗

PubMed1993

Odorant-regulated Ca2+ gradients in rat olfactory neurons.

Olfactory neurons respond to odors with a change in conductance that mediates an influx of cations including Ca2+. The concomitant increase in [Cai] has been postulated to play a role in the adaptation to maintained odorant stimulation (Kurahashi, T., and T. Shibuya. 1990. Brain Research. 515:261-268. Kramer, R. H., and S. A. Siegelbaum. 1992. Neuron. 9:897-906. Zufall, F., G. M. Shepherd, and S. Firestein. 1991. Proceedings of the Royal Society of London, B. 246:225-230.) We have imaged the distribution of [Cai] in rat olfactory neurons (RON) using the Ca2+ indicator fura-2. A large percentage of the RON (42%, n = 35) responded to odorants with an increase in [Cai]. About half of the responding neurons displayed an increase in [Cai] at the apical end of the cell, but not at the soma. Moreover, in those cells that responded to odors with a standing [Cai] gradient, the gradient could be maintained for long periods of time (minutes) provided that the cells were continuously stimulated. In contrast, K(+)-induced depolarization elicited a more homogeneous increase in [Cai]. The spatially inhomogeneous increase in [Cai] elicited by odorants in some cells has important implications for the role of Ca2+ in adaptation because channels and enzymes regulated by Ca2+ will be affected differently depending on their location.

Animals↗

PubMed1993

Rapid kinetic measurements of second messenger formation in olfactory cilia from channel catfish.

The effect of stimulating olfactory cilia from the channel catfish (Ictalurus punctatus) with odorant amino acids on the formation of adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, and inositol 1,4,5-trisphosphate (IP3) was studied in the subsecond time scale using a quenched flow technique. L-Alanine (L-Ala) and L-cysteine (L-Cys) (100 microM) elicited a transient elevation in IP3 levels that peaked at 25 ms. In contrast, even at high concentration a mixture of odorant amino acids (1 mM L-Ala, L-Cys, L-norleucine, L-glutamate, L-proline, and L-arginine) did not elicit a change in cAMP levels in this time scale and caused only relatively slow and minor increases in cGMP. The dose-response relationship for the IP3 response of L-Cys and L-Ala in the range from 10 nM to 1 mM is consistent with previous electrophysiological and ligand binding experiments. Odorant amino acid-stimulated IP3 formation was GTP dependent and was inhibited by guanosine 5'-O-(2-thiodiphosphate), suggesting that the response was G protein mediated. These results are consistent with a mediatory role for IP3 in amino acid olfactory signal transduction in catfish.

Alanine↗

PubMed1992

Characterization of a novel inositol 1,4,5-trisphosphate receptor in isolated olfactory cilia.

Inositol 1,4,5-trisphosphate (InsP3), a product of G-protein-mediated receptor activation of phosphoinositide turnover, plays the role of a second messenger when olfactory neurons are stimulated with certain olfactory stimuli. In this paper we examine the specific binding of [3H]InsP3 to isolated olfactory cilia, microsomes and brain membranes from the channel catfish (Ictalurus punctatus) and, by photoaffinity labelling with an InsP3 analogue (125I-labelled 1-[3-(4-azidosalicyloxy)-aminopropyl]inositol 1,4,5-trisphosphate (125I-ASA-InsP3)], we tentatively identify the major InsP3-binding protein in catfish olfactory cilia. InsP3 binding to ciliary membranes is specific and saturable, with a Kd of 1.10 +/- 0.31 microM and a maximum number of binding sites (Bmax) of 17.6 +/- 5.8 pmol/mg. The rank order for potency of inhibition of [3H]InsP3 binding is Ins(1,4)P2 less than Ins(1,3,4)P3 less than Ins(1,3,4,5)P4 = Ins(1,4,5)P3 less than Ins(2,4,5)P3. Exposure of cilia membranes to u.v. light in the presence of 125I-ASA-InsP3 results in the labelling of a protein with apparent Mr 107,000. Labelling is specifically prevented by Ins(1,4,5)P3, Ins(2,4,5)P3 and Ins(1,3,4,5)P4, but not by Ins(1,4)P2 or Ins(1,3,4)P3. Both specific [3H]InsP3 binding and photoaffinity labelling of the Mr-107,000 protein were displaced by heparin. The Kd and the inhibition of [3H]InsP3 binding and of photoaffinity labelling by inositol phosphates and heparin are consistent with the ability of micromolar concentrations of Ins(1,4,5)P3 [but not Ins(1,3,4)P3] to activate the InsP3-gated currents in patch-clamp experiments with olfactory neurons. These results suggest that InsP3 binding to a Mr-107,000 cilia membrane protein may represent binding to the olfactory InsP3-gated cation channel.

Animals↗

PubMed1992

IP3- and cAMP-induced responses in isolated olfactory receptor neurons from the channel catfish.

Olfactory receptor neurons enzymatically dissociated from channel catfish olfactory epithelium were depolarized transiently following dialysis of IP3 or cAMP (added to the patch pipette) into the cytoplasm. Voltage and current responses to IP3 were blocked by ruthenium red, a blocker of an IP3-gated Ca(2+)-release channel in sarcoplasmic reticulum. In contrast, the responses to cAMP were not blocked by extracellularly applied ruthenium red, nor by L-cis-diltiazem or amiloride and two of its derivatives. The current elicited by cytoplasmic IP3 in neurons under voltage clamp displayed a voltage dependence different from that of the cAMP response which showed marked outward rectification. A sustained depolarization was caused by increased cytoplasmic IP3 or cAMP when the buffering capacity for Ca2+ of the pipette solution was increased, when extracellular Ca2+ was removed or after addition of 20-200 nM charybdotoxin to the bathing solution, indicating that the repolarization was caused by an increase in [Cai] that opened Ca(2+)-activated K+ channels. The results suggest that different conductances modulated by either IP3 or cAMP are involved in mediating olfactory transduction in catfish olfactory receptor neurons and that Ca(2+)-activated K+ channels contribute to the termination of the IP3 and cAMP responses.

Animals↗

PubMed1992

A novel method to differentiate between ping-pong and simultaneous exchange kinetics and its application to the anion exchanger of the HL60 cell.

We have developed a new test to differentiate between ping-pong and simultaneous mechanisms for tightly coupled anion exchange. This test requires the use of a dead-end reversible noncompetitive inhibitor. As an example, we have applied the test to the anion exchanger of the HL60 cell using the salicylic acid derivative 3,5-diiodosalicylic acid (DIS), which reversibly inhibits HL60 cell Cl/Cl exchange. The concentration of DIS that causes 50% inhibition (ID50) increased only slightly as either intra- or extracellular chloride was increased, indicating that DIS inhibits HL60 anion exchange in a noncompetitive manner. In agreement with this observation, plots of the slope of the Dixon plot as a function of 1/[Clo] or 1/[Cli] were fit with straight lines with nonzero intercepts, indicating that DIS does not compete with either of the substrates ([Clo] and [Cli]). The secondary Dixon slope test is based on the fact that, for a dead-end inhibitor such as DIS, the slope of the Dixon plot slope vs. 1/[Cli] (secondary Dixon slope or SDS) is independent of extracellular Cl when the exchange mechanism follows ping-pong kinetics. Similarly, the SDS calculated from a plot as a function of 1/[Clo] is also independent of intracellular Cl for a ping-pong exchanger. In contrast to this prediction, we found that for DIS inhibition of Cl/Cl exchange in HL60 cells the slope of the Dixon plot slope vs. 1/[Cli] decreased by a factor of 2.5-fold when [Clo] was increased from 1 to 11 mM (P < 0.0001). This change in the SDS rules out ping-pong kinetics, but is consistent with a simultaneous model of Cl/Cl exchange in which there are extra- and intracellular anion binding sites, both of which must be occupied by suitable anions in order to allow simultaneous exchange of the ions.

Bicarbonates↗