Acetylcholine-induced Na+ influx in the mouse lacrimal gland acinar cells: demonstration of multiple Na+ transport mechanisms by intracellular Na+ activity measurements

Structural Alterations in Large-scale Brain Networks and Their Relationship with Sleep Disturbances in the Adolescent Population

Although sleep disturbances are highly prevalent in adolescents, neuroimaging evidence on the effects of sleep disturbances on their developing brains remains limited. Therefore, we explored gray matter volumes (GMVs) at the whole-brain level and investigated their relationship to sleep disturbances in a sample of Korean adolescents in the general population. We recruited participants from one middle school and high school. All participants and their legal guardians gave informed consent before participating in our study. We used component 5 of the Pittsburgh Sleep Quality Index to measure sleep disturbances and conducted a voxel-based morphometry-DARTEL procedure to measure GMVs. We performed partial correlation analyses to examine whether the GMVs were associated with sleep disturbances. A total of 56 adolescents participated in this study. Our results revealed that GMVs in multiple global regions were negatively correlated with sleep disturbances. Moreover, most of these identified regions belong to large-scale brain networks categorized by functional neuroimaging studies. We found an association between regional GMVs in multiple global regions involved in large-scale networks and the severity of sleep disturbances in the adolescent population. Based on this evidence and previous neuroimaging evidence, we suggest that structural alterations in the networks may be linked to sleep disturbances.

Oral administration of royal jelly restores tear secretion capacity in rat blink-suppressed dry eye model by modulating lacrimal gland function

Tears are secreted from the lacrimal gland (LG), a dysfunction in which induces dry eye, resulting in ocular discomfort and visual impairment. Honey bee products are used as a nutritional source in daily life and medicine; however, little is known about their effects on dry eye. The aim of the present study was to investigate the effects of honey bee products on tear secretion capacity in dry eye. We selected raw honey, propolis, royal jelly (RJ), pollen, or larva from commercially available honey bee products. Tear secretion capacity was evaluated following the oral administration of each honey bee product in a rat blink-suppressed dry eye model. Changes in tear secretion, LG ATP content, and LG mitochondrial levels were measured. RJ restored the tear secretion capacity and decrease in LG ATP content and mitochondrial levels to the largest extent. Royal jelly can be used as a preventative intervention for dry eye by managing tear secretion capacity in the LG.

Neural regulation of lacrimal gland secretory processes: relevance in dry eye diseases

The lacrimal gland is the major contributor to the aqueous layer of the tear film which consists of water, electrolytes and proteins. The amount and composition of this layer is critical for the health, maintenance, and protection of the cells of the cornea and conjunctiva (the ocular surface). Small changes in the concentration of tear electrolytes have been correlated with dry eye syndrome. While the mechanisms of secretion of water, electrolytes and proteins from the lacrimal gland differ, all three are under tight neural control. This allows for a rapid response to meet the needs of the cells of the ocular surface in response to environmental conditions. The neural response consists of the activation of the afferent sensory nerves in the cornea and conjunctiva to stimulate efferent parasympathetic and sympathetic nerves that innervate the lacrimal gland. Neurotransmitters are released from the stimulated parasympathetic and sympathetic nerves that cause secretion of water, electrolytes, and proteins from the lacrimal gland and onto the ocular surface. This review focuses on the neural regulation of lacrimal gland secretion under normal and dry eye conditions.

Transepithelial bioelectrical properties of rabbit acinar cell monolayers on polyester membrane scaffolds

In our quest to develop a tissue-engineered tear secretory system, we have tried to demonstrate active transepithelial ion fluxes across rabbit lacrimal acinar cell monolayers on polyester membrane scaffolds to evaluate the bioelectrical properties of the cultured cells. Purified lacrimal gland acinar cells were seeded onto polyester membrane inserts and cultured to confluency. Morphological properties of the cell monolayers were evaluated by transmission electron microscopy and immunofluorescence staining for Na(+),K(+)-ATPase and the tight junction-associated protein occludin. Sections revealed cell monolayers with well-maintained epithelial cell polarity, i.e., presence of apical (AP) secretory granules, microvilli, and junctional complexes. Na(+),K(+)-ATPase was localized on both the basal-lateral and apical plasma membranes. The presence of tight cell junctions was demonstrated by a positive circumferential stain for occludin. Bioelectrical properties of the cell monolayers were studied in Ussing chambers under short-circuit conditions. Active ion fluxes were evaluated by inhibiting the short-circuit current (I(sc)) with a Na(+),K(+)-ATPase inhibitor, ouabain (100 microM; basal-lateral, BL), and under Cl(-)-free buffer conditions after carbachol stimulation (CCh; 100 microM). The directional apical secretion of Cl(-) was demonstrated through pharmacological analysis, using amiloride (1 mM; BL) and bumetanide (0.1 mM; BL), respectively. Regulated protein secretion was evaluated by measuring the beta-hexosaminidase catalytic activity in the AP culture medium in response to 100 microM basal CCh. In summary, rabbit lacrimal acinar cell monolayers generate a Cl(-)-dependent, ouabain-sensitive AP --> BL I(sc) in response to CCh, consistent with current models for Na(+)-dependent Cl(-) secretion.

Effect of anion secretion inhibitors on mucin content of airway submucosal gland ducts

In porcine bronchi, inhibition of both Cl- and HCO3- transport is required to block the anion secretion response to ACh and to cause mucus accumulation within ACh-treated submucosal gland ducts [S. K. Inglis, M. R. Corboz, A. E. Taylor, and S. T. Ballard. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L372-L377, 1997]. In this previous study, a combination of three potential HCO3- transport inhibitors [1 mM acetazolamide, 1 mM DIDS, and 0.1 mM dimethylamiloride (DMA)] was used to block carbonic anhydrase, Cl-/HCO3- exchange, and Na+/H+ exchange, respectively. The aim of the present study was to obtain a better understanding of the mechanism of ACh-induced HCO3- secretion in airway glands by determining which of the three inhibitors, in combination with bumetanide, is required to block anion secretion and so cause ductal mucin accumulation. Gland duct mucin content was measured in distal bronchi isolated from domestic pigs. Addition of either bumetanide alone, bumetanide plus acetazolamide, or bumetanide plus DIDS had no significant effect on ACh-induced mean gland duct mucin content. In contrast, glands treated with bumetanide plus DMA as well as glands treated with all four anion transport blockers were almost completely occluded with mucin after the addition of ACh. These data suggest that mucin is cleared from the ducts of bronchial submucosal glands by liquid generated from Cl(-)- and DMA-sensitive HCO3- transport.

Partial cloning and characterization of Slc12a2: the gene encoding the secretory Na+-K+-2Cl- cotransporter

The Slc12a2 gene encodes a widely expressed bumetanide-sensitive Na+-K+-2Cl- cotransporter that participates in various functions such as Cl- secretion and cell volume regulation. We isolated and characterized 75 kilobases of the murine gene encoding the cotransporter. The cotransport protein is encoded by 27 exons. Ribonuclease protection assay and primer extension demonstrated tissue-specific transcription initiation sites located within 270 base pairs upstream of the start codon. Nucleotide sequence analysis of the proximal 5'-flanking region revealed the presence of a weak TATA box, multiple Sp1/GC consensus sites, and the consensus sequence of a putative transcriptional initiator. Transfection of luciferase reporter gene constructs in mouse inner medullary collecting duct (mIMCD-3) cells confirmed the location of the minimal promoter within a 120-base pair fragment upstream of the cDNA. We also report the identification of an alternatively spliced variant of the cotransporter, expressed primarily in brain. This new spliced variant lacks exon 21, which encodes a 16-amino acid peptide located in the COOH-terminal tail of the protein. The absence of this exon causes the loss of the single protein kinase A consensus site of the cotransport protein.

Fluid phase endocytosis by isolated rabbit lacrimal gland acinar cells

It is well known that lacrimal gland acinar cells retrieve secretory vesicle membrane constituents from their apical plasma membranes after stimulated exocytosis of secretory proteins. There have also been indications of a recycling traffic involving the basal-lateral plasma membranes. In an effort to document this traffic, determine how it is regulated, and discern whether it involves more than one intracellular compartment, we studied internalization of the fluid phase marker, Lucifer Yellow, and its relationship to protein release in acinar cells isolated from rabbit lacrimal glands. Loading of intracellular vesicles was apparent with fluoresence microscopy. Stimulation with carbachol increased both the rate of internalization and the intracellular volume equilibrating with extracellular fluid, suggesting the loading of two compartments. A carbachol concentration of 10 microM increased uptake by 80% during 20-min incubations at 37 degrees C. Increasing the carbachol concentration to 1 mM reduced the response by 50%, and it appeared to do so by decreasing the intracellular volume accessible to extracellular fluid, rather than the rate of endocytosis. Carbachol affected protein release differently, increasing it by 50% at 10 microM and 80% at 1 mM. Acceleration of endocytosis by 10 microM carbachol was transient, becoming negligible after 60 min. Vasoactive intestinal peptide (VIP) and isoproterenol increased internalization 35% and 25% respectively; neither reduced uptake at the highest concentrations tested; and only isoproterenol significantly affected protein secretion. Combinations of VIP and carbachol exerted synergistic effects on both fluid phase internalization and protein release. Steady-state uptake at 18 degrees C in the presence of 10 microM carbachol was equal to uptake at 37 degrees C in the absence of carbachol, suggesting a temperature block in the pathway to at least one endocytic compartment. Decreasing the temperature to 18 degrees C eliminated the inhibitory action of excessive carbachol, suggesting that the compartment whose loading was impaired by excessive carbachol was positioned distal to the temperature block. Carbachol accelerated release of marker from preloaded cells, indicating that it stimulated recycling between the plasma membranes and endocytic compartments. This effect was maximal at a concentration of 10 microM and unchanged with increasing concentrations. In accord with the hypothesis that traffic into and out of a certain compartment was particularly dependent on stimulation, a fraction of the marker taken up by optimally stimulated cells at 37 degrees C was retained unless carbachol or VIP was present in the efflux medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Na+ transport processes in isolated guinea pig nasal gland acinar cells

In the dispersed acinar cells of the submucosal nasal gland in the guinea pig, intracellular Na+ concentration ([Na+]i) was measured with a microfluorimetric imaging method and the cytosolic indicator dye, sodium-binding benzofuran isophthalate, under HCO3(-)-free conditions. In the unstimulated condition, the [Na+]i was averaged to 12.8 +/- 5.2 mM. Addition of 100 microM ouabain or removal of external K+ caused an increase in [Na+]i. Replacement of external Cl- with NO3- or addition of 0.5 mM furosemide reversibly decreased the [Na+]i. The recovery process from the reduced [Na+]i was inhibited by removal of either K+ or Cl- in the bath solution. These findings indicate the presence of a continuous influx of Na+ coupled with K+ and Cl- movement. Application of acetylcholine (ACh, 1 microM) caused an increase in [Na+]i by about 15-20 mM, which was completely inhibited by addition of 10 microM atropine. Increased cytosolic Na+ induced by ACh was extruded by the Na(+)-K+ pump. Removal of external Cl- and addition of 50 microM dimethylamiloride inhibited ACh-induced increase in [Na+]i by about 66% and 19%, respectively. In both unstimulated and stimulated state, Na(+)-K+ pump, Na-K-Cl cotransport, and Na(+)-H+ exchange play a critical role in maintaining intracellular electrolyte environment and in controlling a continuous secretion of nasal fluids.

Carbachol-induced increase of Na+/H+ antiport and recruitment of Na+,K(+)-ATPase in rabbit lacrimal acini

Parallel arrays of Na+/H+ and Cl-/HCO3- antiporters are believed to catalyze the first step of transepithelial electrolyte secretion in lacrimal glands by coupling Na+ and Cl- influxes across acinar cell basolateral membranes. Tracer uptake methods were used to confirm the presence of Na+/H+ antiport activity in membrane vesicles isolated from rabbit lacrimal gland fragments. Outwardly-directed H+ gradients accelerated 22Na+ uptake, and amiloride inhibited 96% of the H+ gradient-dependent 22Na+ flux. Amiloride-sensitive 22Na+ influx was half-maximal at an extravesicular Na+ concentration of 14 mM. In vitro stimulation of isolated lacrimal acini with 10 microM carbachol for 30 min increased Na+/H+ antiport activity of a subsequently isolated basolateral membrane sample 2.5-fold, but it did not significantly affect Na+/H+ antiport activity measured in intracellular membrane samples. The same treatment increased basolateral membrane Na+,K(+)-ATPase activity 1.4-fold; this increase could be accounted for by decreases in the Na+,K(+)-ATPase activities of intracellular membranes. Thus, it appears that cholinergic stimulation causes recruitment of additional Na+,K(+)-ATPase pump units to the acinar cell basolateral plasma membrane. The mechanistic basis of the increase in basolateral membrane Na+/H+ antiport activity remains unclear.

Microfluorimetric imaging study of the mechanism of activation of the Na+/H+ antiport by muscarinic agonist in rat mandibular acinar cells

The mechanism of regulation of intracellular pH (pHi) in dispersed acini from the rat mandibular salivary gland has been studied with a microfluorimetric imaging method and the pH probe 2',7'-bis(2-carboxyethyl)-5(and -6)-carboxyfluorescein. The pHi in the TRIS/HEPES-buffered standard solution was 7.29 +/- 0.01. Addition of 1 mumol/l acetylcholine (ACh) or ionomycin caused a sustained increase in the pHi. These agents decreased pHi in the absence of external Na+ or in the presence of amiloride. The rate of pHi recovery from an acid load after NH+4 prepulse was a linear function of pHi and increased as pHi became more acidic. Addition of ACh shifted the relationship towards a more alkaline pHi range. The increase in pHi induced by ACh or ionomycin was not inhibited by the protein kinase C inhibitors staurosporine (10 nM) and 1-(5-isoquinolinesulfonyl)-1-methylpiperazine (50 mumol/l). Addition of 0.1-1 mumol/l phorbol 12-myristate 13-acetate (TPA) had little effect on pHi within 10 min; however, exposure to TPA for 120 min resulted in a significant rise in pHi. In Ca(2+)-free solution with 50 mumol/l 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate, the ACh-induced rise in both pHi and cytosolic Ca2+ concentration was suppressed. ACh and ionomycin caused an increment of amiloride-sensitive acid output into the extracellular fluid, while 20 mumol/l 1-oleoyl-2-acetylglycerol had little effect on it. It was concluded that (a) stimulation with ACh activated the Na+/H+ antiport in the plasma membrane, (b) ACh also stimulated the intracellular acid production but acid extrusion by the Na+/H+ antiport prevented the cell from intracellular acidification, and (c) the major route of signal transduction for the ACh-induced activation of the Na+/H+ antiport was independent of protein kinase C but was dependent on the rise in cytosolic Ca2+ concentration. The implication of the cytosolic acidification and cell volume change in pHi regulation is discussed.

Sodium transport and intracellular sodium activity in cultured human nasal epithelium

Human airway epithelia are predominantly Na(+)-absorbing epithelia. To investigate the mechanisms for Na+ absorption across airway epithelia, the driving forces and paths for Na+ translocation across each membrane were examined with double-barreled Na(+)-selective microelectrodes in cultured human nasal epithelium (HNE). Under control conditions, intracellular Na+ activity (acNa) was 23 +/- 1 mM (n = 44 preparations, 393 impalements). Amiloride (10(-4) M) hyperpolarized the apical membrane and increased the fractional apical membrane resistance but did not affect acNa. Exposure to Na(+)-free luminal solution induced bioelectric responses similar to amiloride but also reduced acNa to 8 +/- 1 mM. Reduction of luminal Na+ concentration ([Na+]) in the presence of amiloride also reduced acNa without further changes in bioelectric parameters. Reduction of serosal [Na+] decreased aNac, a response blocked by bumetanide (10(-4) M). Ouabain (10(-4) M, serosal) led to a reduction in equivalent short-circuit current (Ieq) and increase in acNa. We conclude that 1) acNa is higher in HNE than in most mammalian epithelial cells, 2) the apical membrane expresses a conductive Na+ path, and 3) the basolateral membrane transports Na+ via the Na(+)-K(+)-adenosinetriphosphatase and a Na(+)-K(+)-2Cl- cotransport system.

Effects of intra- and extracellular H+ and Na+ concentrations on Na(+)-H+ antiport activity in the lacrimal gland acinar cells

Kinetic properties of the Na(+)-H+ antiport in the acinar cells of the isolated, superfused mouse lacrimal gland were studied by measuring intracellular pH (pHi) and Na+ activity (aNai) with the aid of double-barreled H(+)- and Na(+)-selective microelectrodes, respectively. Bicarbonate-free solutions were used throughout. Under untreated control conditions, pHi was 7.12 +/- 0.01 and aNai was 6.7 +/- 0.6 mmol/l. The cells were acid-loaded by exposure to an NH4+ solution followed by an Na(+)-free N-methyl-D-glucamine (NMDG+) solution. Intracellular Na+ and H+ concentrations were manipulated by changing the duration of exposure to the above solutions. Subsequent addition of the standard Na+ solution rapidly increased pHi. This Na(+)-induced increase in pHi was almost completely inhibited by 0.5 mmol/l amiloride and was associated with a rapid, amiloride-sensitive increase in aNai. The rate of pHi recovery induced by the standard Na+ solution increased in a saturable manner as pHi decreased, and was negligible at pHi 7.2-7.3, indicating an inactivation of the Na(+)-H+ antiport. The apparent Km for intracellular H+ concentration was 105 nmol/l (pH 6.98). The rate of acid extrusion from the acid-loaded cells increased proportionally to the increase in extracellular pH. Depletion of aNai to less than 1 mmol/l by prolonged exposure to NMDG+ solution significantly increased the rate of Na(+)-dependent acid extrusion. The rate of acid extrusion increased as the extracellular Na+ concentration increased following Michaelis-Menten kinetics (Vmax was 0.55 pH/min and the apparent Km was 75 mmol/l at pHi 6.88).(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of bumetanide, amiloride and Ba2+ on fluid and electrolyte secretion in rabbit salivary gland

1. In order to distinguish between models of anion secretion, the effects of transport inhibitors on saliva flow rate and electrolyte composition were studied during the plateau phase of secretion in rabbit mandibular salivary glands. 2. Bumetanide, an inhibitor of Na+,K+,2Cl- co-transport, inhibited flow rate (by 60%) and reduced Cl- concentration. K+ and HCO3- concentrations were increased. Forskolin, an adenylate cyclase activator which inhibits ductal transport, did not significantly affect this pattern of changes. 3. Amiloride, used at concentrations that would inhibit Na(+)-H+ exchange, inhibited flow rate (by 30%). Cl- concentration was initially increased before subsequently decreasing at the same time as HCO3- concentration increased. These concentration changes can probably be attributed to ductal transport. When amiloride was applied to glands perfused with nominally HCO3- -free solutions, inhibition of flow rate was rapid and almost complete. 4. When amiloride and bumetanide were both present in the perfusate, flow rate was inhibited by 92%. The pattern of electrolyte changes was not significantly different from that observed in the presence of bumetanide alone. 5. Inhibition of K+ channel activity using Ba2+ also inhibited flow rate. Cl- concentration was increased as was K+ concentration. HCO3- concentration was not increased. 6. The anion exchange inhibitor DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid) had no effect on either flow rate or electrolyte concentration. It did, however, elicit secretion in the absence of acetylcholine. 7. The data suggest that Na(+)-H+ and Cl- -HCO3- exchangers are unlikely to be involved in fluid and electrolyte secretion in these glands as suggested by some authors. Most of the data can be explained by postulating the existence of non-specific anion channels in the apical membranes of the acinar cells.

Lacrimal fluid and electrolyte secretion: a review

Lacrimal gland fluid is an important component of the precorneal tear film. The rate of lacrimal gland fluid secretion is controlled primarily by parasympathetic innervation, and it is, apparently, modulated by sympathetic innervation. Lacrimal gland fluid is produced in two stages, secretion of a primary fluid which resembles an isotonic ultrafiltrate of plasma in the acinus-early intercalated duct region, and secretion of a KCl-rich fluid in subsequent ductal elements. Little is known about the electrolyte transport mechanisms of the ductal epithelia. Recent work using a variety of techniques, including tracer flux measurements, intracellular electrical recording, intracellular ion activity measurements, patch clamping, and analytical subcellular fractionation, supports a model for transcellular Cl-secretion in the acinus which involves Cl--selective channels in the apical plasma membrane and an array of Na+/H+ antiporters, Cl-/HCO3-antiporters, K+ channels, and Na,K-ATPase in the basal-lateral plasma membrane.

Effects of muscarinic, alpha-adrenergic, and substance P agonists and ionomycin on ion transport mechanisms in the rat parotid acinar cell. The dependence of ion transport on intracellular calcium

The relationship between receptor-mediated increases in the intracellular free calcium concentration [( Ca]i) and the stimulation of ion fluxes involved in fluid secretion was examined in the rat parotid acinar cell. Agonist-induced increases in [Ca]i caused the rapid net loss of up to 50-60% of the total content of intracellular chloride (Cli) and potassium (Ki), which is consistent with the activation of calcium-sensitive chloride and potassium channels. These ion movements were accompanied by a 25% reduction in the intracellular volume. The relative magnitudes of the losses of Ki and the net potassium fluxes promoted by carbachol (a muscarinic agonist), phenylephrine (an alpha-adrenergic agonist), and substance P were very similar to their characteristic effects on elevating [Ca]i. Carbachol stimulated the loss of Ki through multiple efflux pathways, including the large-conductance Ca-activated K channel. Carbachol and substance P increased the levels of intracellular sodium (Nai) to more than 2.5 times the normal level by stimulating the net uptake of sodium through multiple pathways; Na-K-2Cl cotransport accounted for greater than 50% of the influx, and approximately 20% was via Na-H exchange, which led to a net alkalinization of the cells. Ionomycin stimulated similar fluxes through these two pathways, but also promoted sodium influx through an additional pathway which was nearly equivalent in magnitude to the combined uptake through the other two pathways. The carbachol-induced increase in Nai and decrease in Ki stimulated the activity of the sodium pump, measured by the ouabain-sensitive rate of oxygen consumption, to nearly maximal levels. In the absence of extracellular calcium or in cells loaded with the calcium chelator BAPTA (bis[o-aminophenoxy]ethane-N,N,N',N'-tetraacetic acid) the magnitudes of agonist- or ionomycin-stimulated ion fluxes were greatly reduced. The parotid cells displayed a marked desensitization to substance P; within 10 min the elevation of [Ca]i and alterations in Ki, Nai, and cell volume spontaneously returned to near baseline levels. In addition to quantitating the activation of various ion flux pathways in the rat parotid acinar cell, these results demonstrate that the activation of ion transport systems responsible for fluid secretion in this tissue is closely linked to the elevation of [Ca]i.

Evidence for an anion exchanger in the mouse lacrimal gland acinar cell membrane

Anion exchange transport in the mouse lacrimal gland acinar cell membrane was studied by measuring the intracellular H+ (pHi) and Cl- (aCli) activities with double-barreled ion-selective microelectrodes. In a HCO3- -free solution of pH 7.4 (HEPES/Tris buffered), pHi was 7.25 and aCli was 33 mM. By an exposure to a HCO3- (25 mM HCO3-/5% CO2, pH 7.4) solution for 15 min, aCli was decreased to 25 mM, and pHi was transiently decreased to about 7.05 within 1 min, then slowly relaxed to 7.18 in 15 min. Intracellular HCO3- concentration [HCO3-]i, calculated by the Henderson-Hasselbalch's equation, was 11 mM at 1 min after the exposure and then slowly increased to 15 mM. Readmission of the HCO3(-)-free solution reversed the changes in aCli and pHi. The intracellular buffering power was about 40 mM/pH. An addition of DIDS (0.2 mM) significantly inhibited the rates of change in aCli, pHi, and [HCO3-]i caused by admission/withdrawal of the HCO3- solution and decreased the buffer value. Replacement of all Cl- with gluconate in the HCO3- solution increased pHi, and readmission of Cl- decreased pHi. The rates of these changes in pHi were reduced by DIDS by 32-45% but not by amiloride (0.3 mM). In the HCO3- solution, a stimulation of intracellular HCO3- production by exposing the tissue to 25 mM NH4+ increased aCli significantly. While in the HCO3(-)-free solution or in the HCO3- solution containing DIDS, exposure to NH4+ had little effect on aCli.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanism of uphill chloride transport of the mouse lacrimal acinar cells: studies with Cl- -sensitive microelectrode

The mechanism of uphill Cl- accumulation by mouse lacrimal acinar cells was studied using double-barrelled Cl- -selective microelectrodes. When measured in standard tris-buffered saline solution, the membrane potential (Vm) was -39.2 +/- 0.4 mV and intracellular Cl- activity (AiCl) was 34.6 +/- 0.7 mmol/l which was 1.4 times higher than the equilibrium level. In Na+-free solution, AiCl decreased from 34 mmol/l to 19 mmol/l in 100 min, a level that was close to the equilibrium activity. Return to the standard solution restored the normal level of AiCl in 5 min. In the presence of furosemide (1 mmol/l), Cl- uptake induced by Na+-readmission was inhibited by 44%. Superfusion with a K+-free solution gradually decreased AiCl until it was close to the equilibrium level after 75 min; superfusion with a high-K+ (29.5 mmol/l) solution increased AiCl significantly. In the presence of ouabain (1 mmol/l), switching the superfusing solutions from K+-free to high-K+ and from high-K+ to K+-free at timed intervals of 15 min caused, respectively, an increase (+9 mmol/l) and a decrease (-7 mmol/l) in AiCl. These changes in AiCl were inhibited by furosemide respectively by 61% and 24%. In the presence of furosemide, DIDS (1 mmol/l) or furosemide plus DIDS, the initial rate of Cl- uptake after cessation of acetylcholine (ACh 1 mumol/l) stimulation was inhibited by 47%, 37% or 74%, respectively. Present results show that the characteristics of the uphill chloride uptake by the mouse lacrimal acinar cells are consistent with those of Na+-K+-Cl- cotransport.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation-associated redistribution of Na,K-ATPase in rat lacrimal gland

To test the possibility that stimulation of secretion leads Na,K-ATPase to be recruited from cytoplasmic pools and inserted into basal-lateral plasma membranes, we surveyed the subcellular distributions of Na,K-ATPase in resting and stimulated fragments of rat exorbital lacrimal gland. After a two-dimensional separation procedure based on differential sedimentation and density gradient centrifugation, we defined six density windows, which differ from one another in their contents of biochemical markers. The membranes equilibrating in window I could be identified as a sample of basal-lateral membranes; in resting preparations these membranes contained Na,K-ATPase enriched 16.6-fold with respect to the initial homogenates. Windows II through VI contained various cytoplasmic membrane populations; these accounted for roughly 80% of the total recovered Na,K-ATPase activity. Thirty-minute stimulation with 10 microM carbachol caused a 1.4-fold increase (P less than 0.05) in the total Na,K-ATPase content of window I; this increase could be largely accounted for by a 1.7-fold decrease in the total Na,K-ATPase content of density window V. Acid phosphatase activity also redistributed following stimulation, but it was recruited from a different source, and it was inserted into membranes equilibrating in windows II and III as well as into the membranes of window I.

Differential effects of aldosterone and ADH on intracellular electrolytes in the toad urinary bladder epithelium

Quantitative electron microprobe analysis was employed to compare the effects of aldosterone and ADH on the intracellular electrolyte concentrations in the toad urinary bladder epithelium. The measurements were performed on thin freeze-dried cryosections utilizing energy dispersive x-ray microanalysis. After aldosterone, a statistically significant increase in the intracellular Na concentration was detectable in 8 out of 9 experiments. The mean Na concentration of granular cells increased from 8.9 +/- 1.3 to 13.2 +/- 2.2 mmol/kg wet wt. A significantly larger Na increase was observed after an equivalent stimulation of transepithelial Na transport by ADH. On average, the Na concentration in granular cells increased from 12.0 +/- 2.3 to 31.4 +/- 9.3 mmol/kg wet wt (5 experiments). We conclude from these results that aldosterone, in addition to its stimulatory effect on the apical Na influx, also exerts a stimulatory effect on the Na pump. Based on a significant reduction in the Cl concentration of granular cells, we discuss the possibility that the stimulation of the pump is mediated by an aldosterone-induced alkalinization. Similar though less pronounced concentration changes were observed in basal cells, suggesting that this cell type also participates in transepithelial Na transport. Measurements in mitochondria-rich cells provided no consistent results.