Intracellular pH measurement in primary monolayer cultures of rat epididymal cells

Immunolocalization and regulation of cystic fibrosis transmembrane conductance regulator in the adult rat epididymis

Cystic fibrosis is the most common serious autosomal recessive condition in whites, and more than 95% of men with cystic fibrosis are infertile. The cystic fibrosis transmembrane conductance regulator (CFTR), a cyclic adenosine monophosphate (cAMP)-regulated chloride channel, has been localized in the efferent ducts; however, to our knowledge, its expression and regulation in the epididymis by testicular factors have not been examined. In the present study, these parameters were examined immunocytochemically by the light microscope with an anti-CFTR antibody in Bouin-fixed, paraffin-embedded control adult rat epididymides and both orchidectomized adult rats with or without testosterone supplementation and efferent duct-ligated rats sacrificed at different time points. In control animals, a thick dense band of immunoperoxidase reaction product was visualized over the apical plasma membrane of the principal cells but not their microvilli. The apical band was prominent only in the corpus and cauda regions. While there was no CFTR expression in basal cells, clear cells of the corpus and cauda regions showed a weak-to-moderate band of apical plasma membrane staining. An examination of orchidectomized, orchidectomized and testosterone, and efferent duct-ligated rats revealed that CFTR was no longer expressed as an intense band on the apical plasma membrane of the principal cells of the corpus and cauda regions. However, under these conditions, an intense apical/supranuclear reaction was noted in the form of small vesicular structures. Clear cells were unaffected by the different experimental treatments. Together, these data indicate that CFTR is expressed in a cell- and region-specific manner and that, while its synthesis in principal cells is not under the control of testicular factors, targeting to the apical plasma membrane is regulated by a testicular luminal factor.

Determinants of intracellular pH in gas gland cells of the swimbladder of the European eel Anguilla anguilla

Gas gland cells of the European eel (Anguilla anguilla) were cultured on collagen-coated coverslips, and intracellular pH was measured using the pH-sensitive fluorescent probe 2′,7′-bis-(2-carboxypropyl)-5-(6)-carboxyfluorescein (BCPCF). The contributions of various proton-translocating mechanisms to homeostasis of intracellular pH (pHi) were assessed by adding specific inhibitors of the various proton-translocating mechanisms at a constant extracellular pH (pHe)of 7.4 and after artificial acidification of the cells using the ammonium pulse technique. The greatest decrease in pHi was observed after addition of 5-(N-ethyl-N-isobutyl)-amiloride (MIA), an inhibitor of Na+/H+ exchange. Na+/H+ exchange was active under steady-state conditions at an extracellular pH of 7.4, and activity increased after intracellular acidification. Incubation of gas gland cells with 4,4′-diisothiocyanostilbene-2,2′-disulphonic acid(DIDS), an inhibitor of anion exchange, also caused a decrease in pHi, but this decrease was not as pronounced as in the presence of MIA. Furthermore, at low pHi, the effect of DIDS was further reduced, suggesting that bicarbonate-exchanging mechanisms are involved in maintaining a steady-state pHi but that their importance is reduced at low pH. Bafilomycin A1,a specific inhibitor of the V-ATPase, had no effect on steady-state pHi. However, recovery of intracellular pH after an artificial acid load was significantly impaired in the presence of bafilomycin. Our results suggest that Na+/H+ exchange and anion exchange are important for the regulation of pHi at alkaline values of pHe. When pHi is low, a situation probably often encountered by gas gland cells during gas secretion,Na+/H+ exchange continues to play an important role in acid secretion and a V-ATPase appears to contribute to proton secretion.

Polarized distribution of NHE1 and NHE2 in the rat epididymis

Previous studies from our laboratory have provided evidence that the rat epididymis utilizes the Na(+)/H(+) exchanger to transport acid and base. The present study was undertaken to use immunohistochemistry for investigating the localization (apical versus basolateral) and distribution of NHE1 and NHE2 proteins along intact rat epididymis. Both proteins were found to be exclusively localized within the epithelium. Immunoreactivity for NHE1 was detected on the basolateral surface, whereas NHE2 immunoreactivity was detected on the apical side of the epithelium. Interestingly, NHE1 was found along the entire length of the epididymal tubule whereas NHE2 was absent in the initial segment but present in the caput, corpus, and cauda regions. These results, when interpreted along with those of previous functional studies, may suggest that the apical NHE2 is involved in Na(+) reabsorption and the basolateral NHE1 in HCO(3)(-) secretion in the rat epididymis.

Serotonin via 5-HT1B and 5-HT2B receptors stimulates anion secretion in the rat epididymal epithelium

1. The short-circuit current (Isc) technique was used to study the role of 5-hydroxytryptamine (5-HT) in the regulation of anion secretion in cultured rat cauda epididymal epithelia. 2. 5-HT, the 5-HT1B-selective agonist 5-nonyloxytryptamine (5-NOT) and the 5-HT2B-selective agonist alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT) added basolaterally stimulated Isc in a dose-dependent manner with EC50 values of 0.4, 20 and 0.3 microM, respectively. No other agonists for 5-HT receptors had any effect. 3. The pattern of responses to 5-HT was biphasic. Pretreating the tissues with the 5-HT1B-selective antagonist isamoltane (200 microM) and the 5-HT2B-selective antagonist rauwolscine (200 microM) inhibited the rapid transient phase by 55 and 45 %, whereas the sustained phase could only be blocked by rauwolscine. 4. Removal of chloride or bicarbonate or both from the normal Krebs-Henseleit solution reduced the responses to 5-HT, 5-NOT and alpha-methyl-5-HT to varying degrees. The results suggest that 5-HT1B- and 5-HT2B-mediated responses were mainly due to chloride and bicarbonate secretion, respectively. 5. Manipulation of the cAMP and Ca2+ signal transduction pathways with chemical agents provided evidence that the responses to 5-HT were mediated through cAMP. 6. Piroxicam pretreatment abolished the Isc response to alpha-methyl-5-HT but not to 5-NOT, indicating that the 5-HT2B-mediated response, but not the 5-HT1B-mediated response, is dependent on prostaglandin synthesis. 7. Immunohistochemical studies showed that 5-HT-like immunoreactivity was detected in nerve fibres and in small granular cells surrounding the epididymal tubules. 8. It is suggested that the 5-HT released from serotonergic nerve endings and/or from mast cells regulates electrolyte and fluid secretion in the epididymis.

Intracellular pH responses of hybridoma and yeast to substrate addition and acid challenge

The pHi responses of hybridoma and yeast cells to substrate and external acid additions were measured using the fluorescent pHi indicator, 9-aminoacridine. The pHi change, following CCCP addition, indicated by 9AA, compared very well with that indicated by BCECF. No change in pHi was observed following glucose or glutamine additions to hybridoma cells under glucose- and glutamine-absent conditions. Also, no change in pHi was observed when glucose was added in the presence of low glutamine and when glutamine was added in the presence of low glucose. However, in the presence of amiloride, the pHi of hybridoma cells decreased following glucose addition. Intracellular pH responses of hybridoma and yeast cells to decreases in external pH, effected by acid addition, were dependent on the cellular energy state and acid type. Cells controlled their pHi more tightly under energy-poor conditions compared to energy-rich conditions, and sulfuric acid (strong acid) caused larger changes in pHi compared to pyruvic acid (weak acid). In response to acid addition under energy-rich conditions, the magnitudes of pHi increases in hybridoma were smaller in the presence of amiloride compared to that in the absence of amiloride. Further, pHi responses to a decrease in external pH were slower at submetabolic temperatures.

Studies of transepithelial Cl- transport in cultured cauda epididymal cells of rats by the short-circuit current method

1. Monolayer cultures of cauda epididymides from male Sprague-Dawley rats (210-230 g) were studied by the short-circuit current (ISC) technique to characterize the properties of the transepithelial chloride transport. In HCO(3-)-free, HEPES-buffered solution, adrenaline (0.23 microM) added to the basolateral side led to an increase in ISC and transepithelial conductance (gt). 2. Decreasing apical chloride concentration ([Cl-]a) progressively from 126.7 to 0 mM by substituting chloride with gluconate increased the ISC response to adrenaline (delta ISC) in a linear fashion with a slope of -1.6 x 10(-3) mu equiv h-1 cm-2 per millimolar change in [Cl-]a. Pretreating the tissue with a chloride channel blocker diphenylamine-2-carboxylate (DPC) on the apical side significantly reduced the slope to -4.9 x 10(-4) mu equiv h-1 cm-2 per millimolar change in [Cl-]a. 3. By substituting apical chloride with various anions and measuring the change in ISC upon adrenaline stimulation, the selectivity sequence of the apical anion conductance was found to be NO3- approximately Br- > Cl- > I- > gluconate > isethionate. 4. When the monolayers were bathed with Krebs-Henseleit solution containing 25 mM HCO3- and 5% CO2, the delta ISC at each [Cl-]a as well as the dependence of delta ISC on [Cl-]a (slope = -3.3 x 10(-3) mu equiv h-1 cm-2 per millimolar change in [Cl-]a) were significantly greater than the HCO(3-)-free counterpart. Addition of 0.1 mM acetazolamide or 0.5 mM SITS (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulphonic acid) to the basolateral side significantly reduced the effects of HCO3- and CO2. 5. When the tissues were bathed on both sides with HCO(3-)-free, HEPES-buffered solution and were clamped at various transepithelial potential differences (PDt) from +30 mV (lumen positive) to -30 mV (lumen negative), the relationship between the clamping current response to adrenaline (delta ICL) and the PDt applied was linear. Zero clamping current response was found at -6 mV. Decreasing [Cl-]a to 0 mM reduced the dependence of delta ICL on PDt and delta ICL was positive at all PDt tested. The response of the transepithelial conductance to adrenaline (delta gt) did not depend on the PDt applied but was reduced with decreasing apical chloride concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Chloride channels on epithelial cells cultured from human fetal epididymis

Using single-channel recording techniques, we have detected two types of outwardly rectifying chloride channel on epithelial cells cultured from human fetal epididymis. A small-conductance channel (2.8-5.0 pS) was spontaneously active in 29% of cell-attached patches but rapidly disappeared on patch excision. This channel often occurred in clusters and exhibited slow kinetics with open and closed times of the order of tens or hundreds of msec; an open-state probability that was essentially independent of voltage; and a very low permeability to bicarbonate relative to chloride. Exposing epididymal cells to either forskolin (3 microM) or adrenaline (1 microM) activated this channel (up to 350-fold), suggesting that it may be involved in cyclic AMP-mediated anion secretion by the male reproductive tract. The large-conductance channel (14 to 29 pS) was never detected in cell-attached patches but could be activated by depolarization (40 mV) in 3% of excised, inside-out patches. Once activated, opening of this 'large' channel was voltage independent, and it had a relatively high permeability to both gluconate (Pgluconate/Pchloride = 0.24) and bicarbonate (Pbicarbonate/Pchloride = 0.4). The proportion of excised patches that contained this channel was increased 2.5-fold by prior stimulation of the epididymal cells; however, because the channel was never observed in cell-attached patches its physiological role must remain uncertain.

Effects of amiloride on intracellular pH and thermosensitivity

Amiloride, a diuretic drug, is a potent inhibitor of Na+/H+ exchange through the plasma membrane, and has been reported to enhance thermal damage in tumor cells in vitro. We investigated the possible relationship between changes in the thermal response of SCK mouse mammary tumor cells in vitro and changes in intracellular pH (pHi) due to amiloride in the present study. At a concentration of 0.5 mM, amiloride reduced the shoulder (Dq) without causing significant change in the slope (Do) of the survival curve of SCK cells heated once at 43 degrees C. On the other hand, 0.5 mM of amiloride sensitized thermotolerant cells to heat as shown by a reduction in Do. The presence of amiloride during the interval between the first and second heatings slightly reduced or inhibited the development of thermotolerance. The pHi was measured with the BCECF fluorescence method. The presence of 0.5 mM amiloride significantly reduced pHi in both pH 7.2 and 6.6 medium. Heating the SCK cells at 43 degrees C in pH 7.2 or 6.6 medium also reduced the pHi. The combined effect of heat and amiloride in reducing the pHi of SCK cells was additive. These results suggest that the effects of amiloride on the thermal response of SCK cells might be mediated in part by a decrease in pHi. The possibility that the effects of amiloride on the thermal response of tumor cells are mediated by other biochemical changes, such as inhibition of protein synthesis, however, could not be ruled out.