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PubMed1988

Electrophysiological properties of amphibian late distal tubule in vivo.

This study was undertaken to determine the passive electrophysiological properties of the diffusive barriers of the late distal tubule (LDT) in Necturus. The transepithelial resistance (RT) determined by cable analysis was 1,130 omega.cm2, which puts the LDT in the class of "tight" epithelia. Using two different methods, we did not find significant cell-to-cell electrical coupling. The fractional apical resistance was 0.93, and it did not vary with distance from the current-injecting electrode. Relative permeabilities of K+, Na+, and Cl- during peritubular ion concentration changes were assessed by circuit analysis. The conclusions are as follows. The basolateral cell membrane is highly permeable to K+; its apparent K+ transference number is 0.78. Basolateral chloride transference was very small. Sodium removal from peritubular fluid produced depolarization, suggesting carrier-mediated electrogenic Na+ transport. The high fractional resistance of the apical cell membrane prevented assessment of apical transference numbers. However, Cl- removal from luminal fluid produced cell hyperpolarization; the underlying mechanism has not been established with certainty. The paracellular pathway does not discriminate between Na+, Cl-, and some of their substitutes; it is poorly permeable to gluconate and prefers K+ to Na+.

Algorithms↗
PubMed1991

A calcium-permeable stretch-activated cation channel in renal proximal tubule.

Isolated Necturus proximal tubules were split to expose the apical membrane surface for patch clamping. When both pipette and bath solutions contained only Ca, N-methyl-D-glucamine, and methanesulfonate, inwardly directed Ca currents were observed through a stretch-activated (SA) cation channel with conductance of 18 +/- 1 pS (n = 19). The SA cation channel exhibited little discrimination among Na, K, and Ca but was at least nine times more selective for cations than anions. The channel was not significantly gated by either membrane potential or cytosolic Ca. However, application of 15 cmH2O suction to patch pipette significantly increased the mean number of open channels by a factor of 6.5, from 0.04 +/- 0.02 to 0.26 +/- 0.08 (n = 11). Ca currents through the SA cation channel were reversibly blocked by 10 microM gadolinium, which was applied to outside surface of excised patches. This is similar to gadolinium block of stretch-activated channels in Xenopus oocytes (X.-C. Yang and F. Sachs. Science Wash. DC 243: 1068-1071, 1989). A Ca-dependent, maxi-K channel (92 +/- 9 pS, n = 5) was also found at the apical membrane of the same proximal tubules. In some cases this maxi-K channel appeared to be indirectly activated by pipette suction, raising the possibility that Ca influx through the SA cation channel may regulate K efflux via the maxi-K channel. Such a process could mediate cell volume regulation and maintain electrolyte homeostasis during normal variations in Na-substrate cotransport.

Animals↗
PubMed1992

Stretch- and volume-activated channels in isolated proximal tubule cells.

Apical and basolateral channels were studied in isolated proximal tubule cells of Necturus kidney. Many of these isolated cells maintained their polarity, with clearly delineated apical and basolateral regions. A 20-pS stretch-activated (SA) cation-selective channel was identified at the apical side of these cells. This channel was permeable to Ca, K, and Na but was not significantly gated by either membrane potential or cytosolic Ca. Negative pipette pressure (15 cmH2O) increased the open probability (Po) of this channel from 0.04 +/- 0.02 to 0.26 +/- 0.08 (n = 6). Two types of Ca-independent, mechanosensitive, K-selective (SAK) channels were identified at the basolateral surface of polarized proximal tubule cells, i.e., a 30-pS long-open time (50 +/- 7 ms) channel (n = 9), and a 46-pS short-open time (1.3 +/- 0.7 ms) channel (n = 10). Pipette suction (-12 cmH2O) increased the Po of the short-open time channels from 0.008 to 0.015 and increased the Po of the long-open time channel from 0.03 to 0.19. The effect of swelling was studied with isolated cells suspended at the tip of patch pipettes. A 50% dilution of the bath doubled cell volume, hyperpolarized the membrane potential by 11 +/- 0.7 mV, and increased the Po of the basolateral SAK channels. This was followed by a spontaneous regulatory volume decrease (RVD), repolarization of the membrane potential, and a decrease in Po. In contrast, isosmotic (bath side) replacement of an impermeant anion (methanesulfonate) with a permeant anion (Cl) doubled cell volume in 5 min but without a subsequent RVD. This sustained swelling hyperpolarized the cell potential by 5.5 +/- 0.7 mV (n = 16) and increased the Po of short-open time channel by a factor of 2.3 from 0.03 +/- 0.01 to 0.07 +/- 0.02 (n = 6). The increase in Po was primarily produced by a reduction in the interburst closed time, which decreased from 142 +/- 43 ms in K methanesulfonate to 36 +/- 11 ms in KCl solutions. These results are consistent with the hypothesis that cell swelling activates Ca-independent K channels at the basolateral membrane of renal proximal tubule. Efflux of K through these channels may partially mediate renal cell volume regulation.

Animals↗
PubMed1992

Site of action potential initiation in amphibian retinal ganglion cells.

1. We applied morphological, pharmacological, electrophysiological, and computer simulation techniques to analyze the origin of impulse initiation in amphibian retinal ganglion cells. 2. Morphological studies of retinal ganglion cells in the mudpuppy (Necturus maculosus) and larval tiger salamander (Ambystoma tigrinum) were carried out with the use of either retrograde or intracellular labeling with horseradish peroxidase. These studies identified a characteristic thinning of the axon that begins after the initial segment of axon emerges from the ganglion cell soma or primary dendrite. Morphometric analysis of the thin segment revealed an average length of 74 microns with a standard deviation of 22 microns. For 20 conventionally placed ganglion cells, the length of the thin segment could not be correlated with soma size, initial segment diameter, or distance from the optic disk. There was also little or no correlation for seven displaced ganglion cells. The diameter of the thin segment was below reliable estimation by light microscopy. 3. We studied the possible significance of the thin axonal segment for ganglion cell impulse generation through a combination of electrophysiological recordings (intracellular and whole-cell recordings) together with computer modeling experiments. 4. Electrophysiological experiments are consistent with the idea that the thin segment and cell soma are less excitable than the initial segment region, which appears to be the principal site of initiation of the nerve impulse. The initial segment is that portion of the axon that is bounded by the soma (or proximal dendrite) at its origin and the thin segment at its distal end. 5. Computer simulations of impulse activation were carried out with the use of two different anatomic constraints: one class of simulations did not take into account the thin segment and assumed uniform cylinder conditions, whereas the other class of simulations included a model of the thin axonal segment. These comparative simulations indicate that the thin segment must contain a relatively high density of voltage-gated Na+ channels and support impulse traffic to account for physiological observations on orthodromic and antidromic impulse propagation. In addition, to match the physiological recordings, it is necessary for both the initial segment and the soma compartments to contain moderately high levels of Na+ channels. 6. Our physiological and simulation studies are consistent with the idea that the nerve impulse is normally initiated in the initial segment of axon and then spreads to activate a somatic impulse in the retrograde direction and the axonal impulse in the anterograde direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1992

Physiological and morphological correlations of horizontal cells in the mudpuppy retina.

1. Horizontal cells (HCs) of the mudpuppy (Necturus maculosus) retina were physiologically characterized with the use of intracellular recordings in a superfused, dark-adapted, retina-eyecup preparation. 2. Physiological analysis included an evaluation of rod versus cone input and a determination of the receptive field size with the use of a displaced slit of light. 3. The morphology of HCs was established through intracellular staining with horseradish peroxidase (HRP) and Lucifer yellow mixed in a single electrode. 4. Three types of horizontal cells were identified, each associated with a distinct morphology. Physiological subtypes included luminosity (L) and chromaticity (C) cells. Morphological diversities included single axon-bearing, multiple axon-bearing and, nonaxon-bearing cells. All C-type HCs lacked axons. 5. Approximately 90% of HCs encountered in this study were L-type cells, which received sign-conserving inputs from both rods and cones. These cell types contained one or more long axons that often stretched greater than 500 microns. This group was morphologically diverse, particularly with respect to variations in the number of axons, but we were unable to correlate this diversity with any unique set of physiological properties. 6. Several C-type HCs were identified (n = 8). These cells depolarized to a low-intensity, short-wavelength (SW) stimulus, whereas they hyperpolarized to high-intensity, long-wavelength stimuli. Morphologically, these cells were axonless (n = 4), with relatively small dendritic fields. 7. A third group of HCs were classified as "short wavelength preferring" HCs (n = 7). These cells responded better to a SW stimulus at all intensity levels. They were thus dissimilar to the common L-type HCs, which showed an apparent rod to cone transition as the stimulus intensity increased, suggestive of a shift from rod to cone preference. Morphologically, these cells were axonless (n = 2), but had broader dendritic fields than the C-type HCs. 8. Our observations indicate that the horizontal cell population of the mudpuppy retina is considerably more complex than previously supposed. The existence of both axon-bearing and axonless HCs, which could be correlated with L- and C-type physiology, implies that HCs may support more than one function in outer retina processing.

Animals↗
PubMed1993

Membrane currents evoked by excitatory amino acid agonists in ON bipolar cells of the mudpuppy retina.

1. Whole-cell patch-clamp recordings were obtained from ON bipolar cells in a retinal slice preparation of the mudpuppy, Necturus maculosus. The effects of excitatory amino acid (EAA) agonists applied in the presence of cobalt (2-5 mM) were examined. 2. At the holding potential of -50 mV, L-2-amino-4-phosphonobutanoic acid (L-AP4, 5-10 microM) evoked an outward current accompanied by a conductance decrease. The zero current potential of the L-AP4-evoked current was near 0 mV independent of whether the intracellular Ringer solution contained CsCl or CsCH3SO4. The currents evoked by light were also accompanied by a conductance decrease and reversed near 0 mV. Replacing external sodium with choline or N-methyl-D-glucamine generated an outward current and suppressed the response to L-AP4. The response to L-AP4 was enhanced by removing extracellular calcium and suppressed by increasing extracellular calcium. These results indicate that L-AP4 closes nonspecific cation channels that are blocked by extracellular calcium. 3. In 2 mM cobalt, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA, 50-100 microM) evoked membrane currents that were accompanied by a conductance increase. AMPA-evoked currents exhibited a significant chloride dependence and were suppressed by gamma-aminobutyric acid-A (GABAA) antagonists bicuculline and picrotoxin; a GABA uptake blocker, nipecotic acid; and a glycine antagonist, strychnine. AMPA-induced currents were virtually absent in the presence of 5 mM cobalt and nominally 0 mM extracellular calcium. These results indicate that the conductance increase induced by AMPA in the presence of 2 mM cobalt is largely the result of calcium-dependent synaptic inputs onto GABAA and glycine receptors of ON bipolar cells. 4. N-methyl-D-aspartic acid (250 microM) was ineffective when applied in the presence of 100 microM cadmium or 2 mM cobalt. 5. 1S,3R/1R,3S-1-aminocyclopentane-1,3-dicarboxylic acid (100-200 microM) evoked an outward current accompanied by a conductance decrease and appears to be an agonist at the L-AP4 receptor. 6. The findings of this study suggest that the only type of EAA receptor in mudpuppy ON bipolar cells is the L-AP4 receptor and that L-AP4 receptor activation results in the closing of nonspecific cation channels that are blocked by extracellular calcium.

Amino Acids↗
PubMed1999

IP(3)-Independent release of Ca(2+) from intracellular stores: A novel mechanism for transduction of bitter stimuli.

A variety of substances with different chemical structures elicits a bitter taste. Several different transduction mechanisms underlie detection of bitter tastants; however, these have been described in detail for only a few compounds. In addition, most studies have focused on mammalian taste cells, of which only a small subset is responsive to any particular bitter compound. In contrast, approximately 80% of the taste cells in the mudpuppy, Necturus maculosus, are bitter-responsive. In this study, we used Ca(2+) imaging and giga-seal whole cell recording to compare the transduction of dextromethorphan (DEX), a bitter antitussive, with transduction of the well-studied bitter compound denatonium. Bath perfusion of DEX (2.5 mM) increased the intracellular Ca(2+) level in most taste cells. The DEX-induced Ca(2+) increase was inhibited by thapsigargin, an inhibitor of Ca(2+) transport into intracellular stores, but not by U73122, an inhibitor of phospholipase C, or by ryanodine, an inhibitor of ryanodine-sensitive Ca(2+) stores. Increasing intracellular cAMP levels with a cell-permeant cAMP analogue and a phosphodiesterase inhibitor enhanced the DEX-induced Ca(2+) increase, which was inhibited partially by H89, a protein kinase A inhibitor. Electrophysiological measurements showed that DEX depolarized the membrane potential and inhibited voltage-gated Na(+) and K(+) currents in the presence of GDP-beta-S, a blocker of G-protein activation. DEX also inhibited voltage-gated Ca(2+) channels. We suggest that DEX, like quinine, depolarizes taste cells by block of voltage-gated K channels, which are localized to the apical membrane in mudpuppy. In addition, DEX causes release of Ca(2+) from intracellular stores by a phospholipase C-independent mechanism. We speculate that the membrane-permeant DEX may enter taste cells and interact directly with Ca(2+) stores. Comparing transduction of DEX with that of denatonium, both compounds release Ca(2+) from intracellular stores. However, denatonium requires activation of phospholipase C, and the mechanism results in a hyperpolarization rather than a depolarization of the membrane potential. These data support the hypothesis that single taste receptor cells can use multiple mechanisms for transducing the same bitter compound.

1-Methyl-3-isobutylxanthine↗
PubMed2002

Taste receptor cell responses to the bitter stimulus denatonium involve Ca2+ influx via store-operated channels.

Previous studies in rat and mouse have shown that brief exposure to the bitter stimulus denatonium induces an increase in [Ca2+]i due to Ca2+ release from intracellular Ca2+ stores, rather than Ca2+ influx. We report here that prolonged exposure to denatonium induces sustained increases in [Ca2+]i that are dependent on Ca2+ influx. Similar results were obtained from taste cells of the mudpuppy, Necturus maculosus, as well as green fluorescent protein (GFP) tagged gustducin-expressing taste cells of transgenic mice. In a subset of mudpuppy taste cells, prolonged exposure to denatonium induced oscillatory Ca2+ responses. Depletion of Ca2+ stores by thapsigargin also induced Ca2+ influx, suggesting that Ca2+ store-operated channels (SOCs) are present in both mudpuppy taste cells and gustducin-expressing taste cells of mouse. Further, treatment with thapsigargin prevented subsequent responses to denatonium, suggesting that the SOCs were the source of the Ca2+ influx. These data suggest that SOCs may contribute to bitter taste transduction and to regulation of Ca2+ homeostasis in taste cells.

Animals↗
PubMed1983

Induction of epithelial tight junctions by a light chain protein isolated from a patient with Fanconi's syndrome.

Tight junctions have not been described in the adult human glomerulus. In a 22-year-old patient with kappa light chain proteinuria, tight junctions were observed between glomerular epithelial cell foot processes (kidney biopsy). The light chain isolated from urine proved to have a relatively high isoelectric point. When the light chain was exposed in vitro to the mucosal surface of a 'leaky' epithelium, the Necturus gallbladder, transepithelial resistance and potential difference increased in a concentration-dependent, reversible manner and NaCl dilution potentials decreased, consistent with a reduction in tight-junctional ionic permeability. Gallbladders fixed in situ and freeze-fractured during peak electrophysiological responses revealed an increase in tight-junctional depth. This report indicates that certain light chains, possibly by virtue of a positive charge, may induce changes in epithelial tight junction structure and/or permeability.

Adult↗
PubMed1982

Amphibian neurotensin (NT) is not xenopsin (XP): dual presence of NT-like and XP-like peptides in various amphibia.

To clarify whether xenopsin (XP) is the amphibian counterpart of mammalian neurotensin (NT), extracts of skin, brain, and intestine from representative amphibians were subjected to immunochemical, chromatographic, and biological analyses. The results indicated the dual presence of NT- and XP-like peptides in extracts of tissues from Xenopus laevis, Rana catesbeiana, Rana pipiens, Bufo marinus, Bufo americanus, and Necturus maculosus, which were separated during gel chromatography on Sephadex G-25 and high pressure liquid chromatography on mu-Bondapak C-18. Immunochemical studies, employing three different region-specific antisera toward NT (ox and man) and one antiserum towards XP (Xenopus laevis), indicated that the NT-like peptides shared COOH-terminal homologies with NT and differed at their NH2-termini. TWo classes of NT-like peptides could be distinguished on the basis of their distributions in tissues and their cross-reactivities with the antisera; immunoreactive NT measured using antiserum HC-8 tended to be found primarily in brain and intestine, whereas that reactive with antiserum PGL-4 was most concentrated in stomach, liver, and pancreas. Although also present in brain and intestine, immunoreactive XP was highest in stomach, pancreas, and skin. Partially purified immunoreactive NT and XP obtained from gastrointestinal tissues of Xenopus laevis and Bufo marinus were shown to increase the hematocrit and induce cyanosis in anesthesized rats. These findings indicate the presence of both NT- and XP-like peptides in neural and gastrointestinal tissues from several amphibia and suggest the possibility that XP-like peptides (apart from NT) may exist in other animals.

Amphibians↗
PubMed1991

Ultrastructure of chromatin. II. Three-dimensional reconstruction of isolated fibers.

Electron-microscope tomography has been used to reconstruct isolated, negatively stained chromatin fibers from Necturus maculosus erythrocytes. Tilt series micrographs from +70 degrees to -70 degrees at 5 degrees intervals were obtained, allowing a reconstruction resolution of 3.3 nm for fibers lying parallel to the tilt axis. The fibers were found to be flattened in the plane of the carbon support, and also stained differentially according to the distance from the carbon. A number of methods of presenting the three-dimensional information were explored. Especially useful was an automatic peak search method for locating putative nucleosome positions coupled with the production of a computer-generated model. Other valuable techniques included the generation of projection stereograms and construction of solid models. A peripheral location of nucleosomes in the chromatin fiber was indicated, and helical arrangements of nucleosomes were observed over short regions. However, no long-range ordering of nucleosomes was apparent. The extent to which this lack of order may be the result of events occurring during the preparation of chromatin for electron microscopy is discussed.

Animals↗
PubMed1991

Ultrastructure of chromatin. I. Negative staining of isolated fibers.

The ultrastructure of chromatin fibers isolated from erythrocyte nuclei of Necturus maculosus and contrasted with a number of negative stains is described. Long (greater than 1000 nm) fibers are prepared under ionic conditions that promote fiber integrity, fixed with glutaraldehyde and negatively stained with aurothioglucose, ammonium molybdate, methylamine tungstate, sodium phosphotungstate, uranyl acetate and a uranyl acetate-sodium phosphotungstate sequence. All stains yield images of '30 nm' chromatin fibers, but aurothioglucose gives the most consistent diameter measurements (33 nm, S.D. 3.5 nm), and provides the clearest images of individual nucleosomes. Regions of fiber showing structural order are seen with all stains. The most commonly observed is a regular pattern of oblique cross-striations consistent with the visualization of the 'top' or 'bottom' of a helical structure. There is a significant relationship between fiber diameter and the cross-striation angle, consistent with an extensible chromatin fiber. Examination of power spectra prepared from selected ordered regions confirms the visual impressions, and indicates a striation spacing ranging from 11 nm to 18 nm, and dependent on the stain type. Fibers allowed to unfold slightly in a buffer containing 50 mM monovalent ions show evidence of a two-stranded helix-like organization. These results are discussed in terms of current models for the structure of the chromatin fiber.

Animals↗
PubMed1983

Fluid transport by gallbladder epithelium.

The absorption of fluid by epithelial tissues is thought to be due to the existence of hypertonic regions within the epithelium. The magnitude of the required hypertonicity as well as its localization have been the subject of considerable experimental and theoretical effort. Model calculations demonstrated the need for knowledge of the water permeability of the membranes of epithelial cells for the purpose of estimation of the osmotic gradients required for fluid absorption. We measured the hydraulic water permeability of the individual cell membranes of Necturus gallbladder by quantitative light microscopy. The water permeabilities were sufficiently high so that small osmotic gradients were required to achieve normal rates of fluid transport. The cell osmolality was calculated to exceed that of the mucosal bathing solution by about 2 mosmol kg-1, and the basolateral interstitial osmolality was calculated to be about 1 mosmol kg-1 greater than that of the cell. The fluid absorbed by the epithelium must be slightly hypertonic to the bathing solutions. Knowledge of the apical cell membrane water permeability and the relative area of the cell and tight junction allow a calculation of the relative flow of fluid across both pathways. It can be readily shown that osmotically induced flow across the epithelium occurs predominantly transcellularly because of the small area of the junctional pathway and the high water permeability of the cell membranes.

Animals↗
PubMed2000

Neuromodulatory effects of gonadotropin releasing hormone on olfactory receptor neurons.

The terminal nerve is an anterior cranial nerve that innervates the lamina propria of the chemosensory epithelia of the nasal cavity. The function of the terminal nerve is ambiguous, but it has been suggested to serve a neuromodulatory role. We tested this hypothesis by exposing olfactory receptor neurons from mudpuppies (Necturus maculosus) to a peptide, gonadotropin releasing hormone (GnRH), that is found in cells and fibers of the terminal nerve. We used voltage-clamped whole-cell recordings to examine the effects of 0. 5-50 micrometer GnRH on voltage-activated currents in olfactory receptor neurons from epithelial slices. We found that GnRH increases the magnitude, but does not alter the kinetics, of a tetrodotoxin-sensitive inward current. This increase in magnitude generally begins 5-10 min after initial exposure to GnRH, is sustained for at least 60 min during GnRH exposure, and recovers to baseline within 5 min after GnRH is washed off. This effect occurred in almost 60% of the total number of olfactory receptor neurons examined and appeared to be seasonal: approximately 67% of neurons responded to GnRH during the courtship and mating season, compared with approximately 33% during the summer, when the sexes separate. GnRH also appears to alter an outward current in the same cells. Taken together, these data suggest that GnRH increases the excitability of olfactory receptor neurons and that the terminal nerve functions to modulate the odorant sensitivity of olfactory receptor neurons.

Animals↗
PubMed1977

Effects of radiation upon the light-sensing elements of the retina as characterized by scanning electron microscopy.

A model system using Necturus maculosus, the common mudpuppy, was established for evaluating effects of radiation upon the light-sensing elements of the retina. Accelerated heavy ions of helium and neon from the Berkeley Bevalac were used. A number of criteria were chosen to characterize radiation damage by observing morphological changes with the scanning electron microscope. The studies indicated retina sensitivity to high-LET (neon) particles at radiation levels below 10 rads (7 particles per visual element) whereas no significant effects were seen from fast helium ions below 50 rads.

Animals↗
PubMed1987

Organization of a vertebrate cardiac ganglion: a correlated biochemical and histochemical study.

A correlated biochemical and histochemical study was undertaken to identify and quantify the presence of different biogenic amines and a substance P-like peptide within the parasympathetic cardiac ganglion of the mudpuppy (Necturus maculosus). Tissue extracts of the cardiac septum containing the parasympathetic cardiac ganglia from control animals were found, by high-pressure liquid chromatography, to contain significant amounts of norepinephrine (NE), epinephrine (E), dopamine (DA), and 5-HT. To allow neural elements of extraganglionic origin to degenerate, ganglia were explanted and maintained in organ culture for 8 d. Extracts from these explanted preparations had no detectable level of E, and NE was reduced, whereas DA and 5-HT levels were similar to those of control preparations. The results indicated that some of the neurons intrinsic to the cardiac septum contain DA and 5-HT and that most (greater than 70%) of the E and NE found in this tissue is of extrinsic origin. Histochemistry of control and explanted preparations showed 5-HT-immunoreactive and catecholamine-containing intrinsic neurons. A substance P-like peptide was identified by radioimmune assay in septal extracts. The peptide content diminished by one-third to one-fifth in preparations maintained in organ culture for 8-14 d, suggesting that a significant amount of the substance P-like peptide is derived from extraganglionic sources. Immunocytochemical studies demonstrated the presence of numerous long substance P-immunoreactive fibers coursing across the septum, branching over cardiac muscle fibers, and forming pericellular networks around individual parasympathetic ganglion cells and clusters of ganglion cells. In addition, numerous small intrinsic neurons exhibited immunoreactivity for substance P. Comparison of the substance P-staining patterns in control and explanted ganglia suggests that the majority of the long substance P-immunoreactive fibers innervating the mudpuppy cardiac ganglion cells are not parasympathetic preganglionic fibers. Rather, it is hypothesized that these fibers are processes of primary sensory fibers. The present observations indicate that the mudpuppy cardiac ganglion exhibits a complex organization similar to that of mammalian sympathetic and enteric ganglia.

Animals↗
PubMed1987

Intracellular pH (pHi) in gastric surface epithelium is more susceptible to serosal than mucosal acidification.

Intracellular microelectrode techniques were used to examine the effects of mucosal or serosal acidification on intracellular pH (pHi) in gastric surface epithelial cells. Necturus antrum was mounted in a modified Ussing chamber, and pHi was determined from the difference between the potentials recorded by intracellular conventional and pH-sensitive microelectrodes. In tissues bathed with bicarbonate-buffered Ringer's solution (pH 7), acidification of the mucosal solution to pH 4.5 by isotonic replacement of the NaHCO3 with NaCl had no significant effects on pHi. In contrast, acidification of the serosal solution to pH 4.5 by replacing the bicarbonate reduced pHi from 7.32 +/- 0.04 to 6.95 +/- 0.06 (p less than 0.001, n = 8). Similarly, in tissues bathed with HEPES-buffered Ringer's solution (pH 7.0), pHi was unaffected by reducing the mucosal solution pH to 4.5 with HCl but fell 0.21 +/- 0.05 pH units (p less than 0.01, n = 7) during acidification of the serosal solution to pH 6. These results suggest that gastric epithelium is more sensitive to acidification from the serosal than the mucosal side. Such a finding is consistent with the concept of a gastric mucosal barrier to luminal acid. It may also explain the gastric epithelium's greater sensitivity to acute ulceration during systemic acidosis.

Animals↗
PubMed1986

Comparative morphometric study of the vestibular system of the vertebrata: reptilia, aves, amphibia, and pisces.

Morphometric measurements were made from serial sections of the vestibular system in four classes of vertebrates: Reptilia, Aves, Amphibia, and Pisces. Representative species of reptile studied were the lizard (Gekko gecko), the common garter snake (Thamnophis sp.), and the common turtle (Chelonia sp.). The budgie (Melopsittacus undulatas), the common pigeon (Columba domestica), the yellow-bellied sapsucker (Sphyrapicus varius), and the horned owl (Bubo virginianus) were chosen as representative of the bird. For the amphibian, the leopard frog (Rana pipiens), and the mud puppy (Necturus maculatus) were chosen for study. As representative of the fish, the goldfish (Carassius auratus), the tilapia (Tilapia mossambica), the guppy (Lebistes sp.), and the sea horse (Hippocampus sp.) were used in these measurements. The morphometric data obtained were then used in estimates of the time constants in the Steinhausen equation which describes the biophysics of fluid flow in the semicircular canals. In general, the time constants (theta/II in the Steinhausen equation) of these representatives of Reptilia, Aves, and Amphibia were of magnitude similar to those reported in mammals, despite the dissimilarities in the diameters of the ducts, the duct radii of curvature, the dimensions of the cristae ampullares and the utricle, and volumes of endolymph within the vestibular system. However, the short-time constants in Pisces were larger (therefore providing a slower response) than those in other vertebrates, and were similar to that of the turtle and the mud puppy.

Amphibians↗