Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Necturus”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15Linked to original sources
PubMed1988

Rheogenic transport of basic and acidic amino acids across the brush border of Necturus small intestine.

In studies with isolated Necturus intestine, glutamate (Glu-) and Na+ each enhanced the mucosal influx of the other. Measurement of apical membrane potential, Va, with microelectrodes revealed a rapid depolarization with addition of 10 mM mucosal Glu-. This depolarization was Na+ dependent. Upon complete removal of Cl- from the bathing medium Va hyperpolarized and the Glu- -induced depolarization increased significantly. However, removal of Cl- did not alter the total Glu- influx. These data suggest that external Cl- attenuates the rheogenicity of Na+/Glu- cotransport in the apical membrane of the absorptive cells. We have presented a model consistent with these observations in which Cl- competes with one -COO- group of Glu- for its binding site on the carrier. The two complexes which may form, carrier/Glu-/2Na+ or carrier/Glu-/2Na+/Cl-, allow for either electrogenic or electroneutral transport of Glu-, depending on the ratio [Glu-]/[Cl-] in the extracellular fluid. In other experiments, addition of mucosal L-lysine (Lys+) induced a rapid depolarization of Va. In the presence of Na+, the depolarization appeared to be saturable with respect to Lys+ concentration. In Na+-free media, however, the depolarization increased with Lys+ concentration up to a maximum at 10 mM and then decreased to near zero at 30 mM. These data are consistent with a model for Lys+ entry in which an anionic site of the carrier can bind either Na+ or the epsilon-NH3+ group of Lys+. In this model transport of either complex, carrier-/Lys+ or carrier-/Lys+/Na+ (and return of the carrier to the extracellular surface) is rheogenic. However, at higher Lys+ concentrations, the epsilon-NH3+ group of a second Lys+ molecule may bind to the carrier forming a complex, carrier-/2Lys+, which is not transported.

Amino Acids↗
PubMed1985

Addition of cAMP to mucosal or serosal medium induces different actions on Necturus gallbladder.

Open tip and Cl(-)-selective microelectrodes were used to study the effects of cAMP on apical membrane potential (Va), fractional voltage ratio (fa) and intracellular chloride activity (aicl) in Necturus gallbladder under open-circuit conditions. In the presence of cAMP in the mucosal medium Va depolarized from -68 +/- 5 mV in control conditions to -56 +/- 5 mV and fa decreased from 0.56 +/- 0.15 in control conditions to 0.15 +/- 0.02. Concomitantly aicl fell from 15 +/- 2 mM to 8 +/- 3 mM, a value close to its electrochemical equilibrium activity. These results differ markedly from those obtained when cAMP was added to serosal medium and indicate that cAMP elicits different transport mechanisms whether it is added to the serosal medium or to the mucosal medium.

Animals↗
PubMed1988

Effects of muzolimine on the late distal tubule of necturus kidney.

The in vivo effects of the diuretic muzolimine were studied in the late distal tubule of the amphibian Necturus. Conventional and ion-selective microelectrodes were used to determine basolateral membrane potential, intracellular Cl- activity and luminal activities of Cl- and K+. Muzolimine depolarized basolateral membrane potential by about 30 mV in 1 min, in a reversible fashion. We attributed this depolarization to blockade of a K+ conductance, because the effects of muzolimine and barium on the highly K-selective basolateral membrane were not additive. In addition, muzolimine elicited a reversible increase of intracellular Cl- activity from 7.5 +/- 0.5 to 14.5 +/- 2.6 mM (concomitant to the basolateral membrane potential depolarization) and of luminal activities of Cl- from 12.4 +/- 1.5 to 22.3 +/- 2.5 mM, within approximately 1 min; both disturbances relaxed toward control values after withdrawal of the diuretic. That muzolimine increases Cl- activity in both the cell and the lumen of the late distal tubule (Cl- is accumulated in these compartments), indicates that retention of Cl- results from hindrance of the basolateral exit step rather than of apical Cl- uptake. Inasmuch as muzolimine failed to increase the luminal activity of K+, Cl- is believed to accumulate in the lumen as NaCl, not KCl.

Animals↗
PubMed1994

Bidirectional synaptic transmission in Necturus taste buds.

Pairs of taste cells were impaled with intracellular recording microelectrodes in intact taste buds in slices of Necturus lingual epithelium. Applying short pulses of 140 mM KCl or 200 mM CaCl2 solutions to the apical pore elicited receptor potentials in taste receptor cells. Chemostimulation of receptor cells elicited postsynaptic responses in basal cells in the taste bud. Postsynaptic responses in basal cells had a threshold for activation and did not saturate with increasing doses of chemical stimulus applied to the receptor cells. We directly depolarized individual receptor cells and tested whether this would evoke postsynaptic responses in basal cells. Depolarizing receptor cells to approximately 0 mV evoked small depolarizing responses in basal cells in 16% of the experiments. The properties of these responses were consistent with their being mediated by a chemical synapse. A comparison of the responses in basal cells evoked by depolarizing single receptor cells, with responses evoked by stimulating the entire receptor cell population with KCl suggests that there is extensive synaptic convergence from receptor cells onto each basal cell. We also tested whether electrical excitation of basal cells would elicit (retrograde) synaptic responses in receptor cells. Single depolarizing pulses (up to 1 sec duration) applied to basal cells through the intracellular recording microelectrode never evoked synaptic responses in receptor cells. However, when repetitive electrical stimuli were applied to basal cells (four to six 1 sec depolarizations to approximately 0 mV every 12 sec) we observed prolonged effects on receptor cells in 11 of 23 experiments. These effects included an increase in the amplitude of receptor potentials elicited by KCI (mean +/- SD = +19 +/- 5%), an increase in membrane input resistance of receptor cells (+27 +/- 11%), and a hyperpolarization of receptor cells (3-10 mV). In control experiments, repetitive stimulation of one receptor cell never elicited such effects in another receptor cell. We investigated the possibility that serotonin (5-HT), released from basal cells, mediated the above modulatory effects on receptor cells. Bath-applied 5-HT (100 microM) mimicked the effects produced by repetitive basal cell stimulation (KCI responses increased by 23 +/- 12%; input resistance increased by 24 +/- 11%; hyperpolarization of 5-15 mV; N = 14). We conclude that basal cells release 5-HT onto adjacent taste receptor cells and that this enhances the electrotonic propagation of receptor potentials from the apical (chemosensitive) tip to the basal (synaptic) processes of receptor cells. The net effect is that activation of basal cells effectively increases the chemosensitivity of taste receptor cells.

Animals↗
PubMed1997

Bitter taste transduction of denatonium in the mudpuppy Necturus maculosus.

Bitter substances are a structurally diverse group of compounds that appear to act via several transduction mechanisms. The bitter-tasting denatonium ion has been proposed to act via two different G-protein-regulated pathways, one involving inositol 1,4, 5-trisphosphate and raised intracellular calcium levels, the other involving phosphodiesterase and membrane depolarization via a cyclic nucleotide-suppressible cation channel. The aim of the present study was to examine these transduction mechanisms in taste cells of the mudpuppy Necturus maculosus by calcium-imaging and whole-cell recording. Denatonium benzoate increased intracellular calcium levels and induced an outward current independently of extracellular calcium. The denatonium-induced increase in intracellular calcium was inhibited by U73122, an inhibitor of phospholipase C, and by thapsigargin, an inhibitor of calcium transport into intracellular stores. The denatonium-induced outward current was blocked by GDP-beta-S, a blocker of G-protein activation. Neither resting nor denatonium-induced intracellular calcium levels were affected by inhibition of phosphodiesterase (with IBMX) or adenylate cyclase (with SQ22536) or by raising intracellular cyclic nucleotides directly (with cell permeant analogs). Our results support the hypothesis that denatonium is transduced via a G-protein cascade involving phospholipase C, inositol 1,4,5-trisphosphate, and raised intracellular calcium levels. Our results do not support the hypothesis that denatonium is transduced via phosphodiesterase and cAMP.

1-Methyl-3-isobutylxanthine↗
PubMed1977

Sex differences in Necturus urinary bladders.

We describe morphological sex differences in urinary bladders of the urodele amphibian Necturus maculosus. The mucosal epithelial cells of bladders from males were tall and contained considerable PAS-positive material. In scanning electron micrographs of the mucosal surface, epithelial cells from male bladders were well demarcated and were capped with microplicae or with long cilia. The mucosal epithelial cells of bladders from females were low and contained only a small amount of PAS-positive material; in scanning electron micrographs cell boundaries could not be distinguished and no cilia or microplicae were present. Bladders from males had higher transepithelial potential difference and lower water content than bladders from females. Urine analyses were not significantly different in the two sexes. It is suggested that response to androgens in the male accounts for the observed differences.

Animals↗
PubMed1977

The central projections in the retina in Necturus maculosus.

The projections of the retina in Necturus maculosus were studied by injecting radioactive proline into one eye. Labeling was seen in both the contralateral and ipsilateral diencephalon and tectum. The contralateral fibers are divided into three major tracts: the marginal, axial, and basal. The ipsilateral fibers separate into a marginal and an axial optic tract. The contralateral and ipsilateral axial optic tracts have a similar distribution. The contralateral and ipsilateral marginal optic tracts projecting to the diencephalon also have a similar distribution. However, in the tectum the ipsilateral marginal optic tract ends in the anterior third while the contralateral extends almost the entire length of the tectum. The retinotectal ipsilateral projection ends in clumps as has been described in other vetebrates. A direct ipsilateral retinotectal projection has not been described in any other amphibian.

Animals↗
PubMed1980

Electron microscopic and autoradiographic studies on vitellogenesis in Necturus maculosus.

Electron microscope studies on Necturus maculosus oocytes ranging in size from 1.1-1.5 mm in diameter indicate the primary proteinaceous yolk to arise within structures referred to in other amphibian oocytes as yolk precursor sacs or bodies. The origin of these yolk precursor sacs appears to result from the activity of the Golgi complexes which form multivesicular and granular-vesicular bodies, the limiting membrane of which is at times incomplete. During differentiation, the yolk precursor sacs contain small vesicles similar in size to Golgi vesicles, larger vesicles similar to vesicular elements of the agranular endoplasmic reticulum and, on occasion, a portion of a mitochondrion. The interior of these sacs becomes granular, perhaps by a dissolution of the components just described, and soon becomes organized into a crystalline configuration. In oocytes 2.0-2.5 mm in diameter, an extensive micropinocytotic activity begins, continues throughout vitellogenesis, and constitutes the primary mechanism for the formation of secondary yolk protein. Numerous coated and smooth-surfaced vesicles, as well as electron-dense and electronlucent ones, fuse in the cortical ooplasm to form progressively larger yolk platelets.

Animals↗
PubMed1975

A further study of the fine structure and membrane properties of neuroglia in the optic nerve of Necturus.

The optic nerve of Necturus maculosus consists of a homogeneous population of astroglia and bundles of unmyelinated axons. The glial cell processes ramify within the nerve roughly delineating fascicles of axons and come together at the periphery to form a complete external limiting membrane interrupted only by narrow clefts between adjacent processes. They are frequently "attached" to one another, forming specialized junctions. Blood vessels are entirely outside the nerve which is surrounded by a basal lamina. The temperature dependence of the glial membrane potential is accurately predicted by the Nernst relation. The membrane potential is unaffected by changes in Cl, Na, Li, and guanidinium which are apparently impermeant. The permeability of the glial membrane to other cations is in the sequence Tl greater than K greater than Rb greater than Cs greater than NH4. This suggests that the chemical nature of the site of potassium permeability in glial cells is similar to that in the neuron.

Animals↗
PubMed1978

The AC impedance of Necturus gallbladder epithelium.

The impedance of Necturus gallbladder epithelium was determined using sine wave currents of 1 Hz to 30 kHz. In control Ringer's solution the impedance locus exhibited a simple semicircle with minute shift of the high frequency end along the real axis and a minute depression of the center below the real axis (average 0.9 +/- 0.7 degrees). Neglecting the slight suppression, the impedance of 1 cm2 of epithelium can be represented by an electrical analogue consisting of a parallel RC element of 115 +/- 26 omega and 5.16 +/- 0.9 muF in series with a small resistor of 5.3 +/- 1.3 omega. In agreement with experimental results obtained under ionic or osmotic substitutions, the applicability of this simple RC analogue to gallbladder epithelium under control conditions can be explained by the influence of the paracellular shunt and by assuming the time constants of the apical and basal cell membranes to be comparable. Based on these data and on voltage divider measurements obtained with microelectrodes the capacitances of the apical and basal cell membrane can be estimated to be approximately 7 and approximately 18 muF/cm2. The latter value agrees well with estimates of the surface folding obtained from electromicrographs, if the specific cell membrane capacitance is assumed to be approximately 1 muF/cm2 as in other cell membranes.

Animals↗
PubMed1976

Transepithelial potential difference in the proximal tubule of necturus kidney.

Transepithelial potential difference (p.d.) was measured in the proximal tubule of Necturus kidney in vivo, by means of microelectrodes filled either with a 3M KClion or with a Ringer's solution for amphibians. The average transepithelial p.d., measured with KCl-tips, was: -1.4 +/- 2.4 mV (early convolutions), -0.1 +/- 2.0 mV (middle convolutions) and +0.1 +/- 2.4 mV (straight segment). The corresponding values obtained with Ringer's-filled microelectrodes were -2.3 +/- 1.8 mV, -1.3 +/- 1.1 mV and +0.1 +/- 1.2 mV, respectively. Tip localization into the lumen was ascertained by luminal injection of either oil (KCl electrode measurements) or artificial solutions which produced a measurable shift of transepithelial p.d. (determinations obtained with Ringer's-tips). Transepithelial p.d. in split-drops (mean reabsorptive half time 27.1 +/- 2.5 min) was -1.8 +/- 1.1 mV. The magnitude of transepithelial p.d. is discussed with respect to an equivalent electrical circuit; it is shown that high transepithelial p.d.'s are inconsistent with the known values of relative conductances of cell membranes in series and shunt pathway, respectively.

Animals↗
PubMed1975

Electrical properties of the cellular transepithelial pathway in Necturus gallbladder. I. Circuit analysis and steady-state effects of mucosal solution ionic substitutions.

Microelectrode techniques were employed to measure the electrical resistance of the cell membranes and the shunt pathway, and the equivalent electromotive forces (EMF's) at both cell borders in Necturus gallbladder epithelium. The cell is, on the average, 57 mV negative to the mucosal solution and 59 mV negative to the serosal solution. The transepithelial potential (Vms) ranges from 0.5 to 5 mV, serosal solution positive. Assuming that the shunt EMF (Vs) is zero with standard Ringer's bathing oth sides of the tissue, both cell membrane EMF's are oriented with the negative pole toward the cell interior and are 39.9 +/- 3.6 mV (apical, Va), and 69.4 +/- 1.8 mV (basal-lateral, Vb)...

Animals↗
PubMed1975

Electrical properties of the cellular transepithelial pathway in Necturus gallbladder. II. Ionic permeability of the apical cell membrane.

Microelectrode techniques were employed to study the ionic permeability of the apical cell membrane of Necturus gallbladder epithelium. Results obtained from continuous records in single cells, and from several cellular impalements shortly after a change in solution, were similar and indicate that both the apical membrane equivalent electromotive force (Va) and electrical resistance (Ra) strongly depend on external [K]. Cl substitutions produced smaller effects, while the effects of Na substitutions with N-methyl-D-glucamine on both Va and Ra were minimal. These results indicate that the permeability sequence of the apical membrane is PKgreater thanPClgreater than PNa. From the calculated absolute value of PNa it is possible to estimate the diffusional Na flux from the mucosal solution into the cells (from the cell potential and an assumed intracellular Na concentration). The calculated flux is roughly three orders of magnitude smaller than the measured net transepithelial flux in this tissue and in gallbladders of other species. Thus, only a minimal portion of Na entry can be attributed to independent diffusion. From estimations of the electrochemical potential gradient across the apical membrane, Cl transport at that site must be active. At the serosal cell membrane, Na transport takes place against both chemical and electrical potentials, while a significant portion of the Cl flux can be passive, if this membrane has a significant Cl conductance. The changes in shunt electromotive force and in transepithelial potential after mucosal substitutions were very similar, indicating that transepithelial bi-ionic potentials yield appropriate results on the properties of shunt pathway.

Animals↗
PubMed1975

Anion permeation in the proximal tubule of Necturus kidney: the shunt pathway.

The effect of foreign anions on transepithelial potential difference and transepithelial input conductance was studied in the isolated perfused Necturus kidney. Two microelectrodes (recording and current-injecting) were inserted into the lumen of single proximal tubules and the peritubular perfusate was shifted reversibly for 30-60 sec from a physiologic Ringer's solution to a test solution in which chloride was replaced isosmotically by a foreign anion. The permeability sequence, obtained by potential measurements, was: lactate less than glutamate less than gluconate less than pyruvate less than benzene sulfonate less than or equal to acetate less than or equal to F less than propionate less than BrO3 less than formate less than ClO3 less than Cl than ClO4 less than I less than or equal to Br less than NO3 less than SCN. Transepithelial conductance decreased when the tissue was perfused with anions less permeable than chloride but the conductance sequence was different from the permeability sequence. Such discrepancies were more pronounced during perfusion with hyperpolarizing anions; ClO4 and I- (both more permeable than chloride) produced an important decrease in transepithelial conductance, followed by incomplete reversibility when the perfusion was shifted again to chloride Ringer's. The results are best explained by the presence of weak positive fixed charges, governing anion permeation, at the shunt pathway of the proximal tubule. An analysis of the data allows tentative estimates of shape and size of the sites.

Animals↗
PubMed1979

Electrical properties of the cellular transepithelial pathway in Necturus gallbladder: III. Ionic permeability of the basolateral cell membrane.

The ionic permeability of the basolateral membrane of Necturus gallbladder epithelium was studied with intracellular microelectrode techniques. After removal of most of the subepithelial tissue (to reduce unstirred layer thickness), impalements were performed from the serosal side, and ionic substitutions were made in the serosal solution while a microelectrode was kept in a cell. Thus, it was possible to obtain continuous (and reversible) records of transepithelial and cell membrane potentials and to measure intermittently the transepithelial resistance and the ratio of cell membrane resistances. From these data and the mean value of the equivalent resistance of the cell membranes in parallel (obtained from cable analysis in a different group of tissues), absolute cell membrane and shunt resistances and equivalent electromotive forces (emfs) were calculated. From the changes of basolateral membrane emf (Eb) produced by the substitutions, the conductance (G) and permeability (P) of the membrane for K, Cl and Na were estimated. Potassium-for-sodium substitutions produced large reductions of both cell membrane potentials, of Eb, and of the resistance of the basolateral membrane (Rb), indicating high GK and PK. Chloride substitution with isethionate or sulfate resulted in smaller changes of cell membrane potentials and Eb and in no significant change of Rb, indicating small but measurable values of GCl and PCl. Sodium substitutions with N-methyl-D-glucamine (NMDG) resulted in cell potential changes entirely attributable to the biionic potential produced in the shunt pathway (PNa greater than PNMDG), and in no significant changes of Rb or Eb, indicating that GNa and PNa are undetectable. The question of the mechanism of Cl transport across the basolateral membrane was addressed by comparing the mean rate of transepithelial Cl transport : formula, see text: and the predicted passive Cl flux across the basolateral membrane (from the membrane Cl conductance, potential, and Cl equilibrium potential). The conclusion is that only a very small fraction of the Cl flux across the basolateral membrane can be electrodiffusional. Since the paracellular Cl conductance is also too low to account for : formula, see text:, these results suggest the presence of a neutral mechanism of Cl extrusion from the cells. This could be a NaCl pump, a downhill KCl transport mechanism, or a Cl-HCO3 exchange mechanism.

Animals↗
PubMed1977

Intracellular gradients of electrical potential in the epithelial cells of the Necturus gallbladder.

When single-barrelled electrodes (5-60 Momega) were advanced under manual control from the mucosal side of the epithelium the mucosal membrane was on average indented by about 40 micron before the microelectrode pentrated the cell. Since this dimpling was comparable with the total depth of the cell, which recovered its original shape within 0.5 sec, the steady intracellular potential was recorded only about 14 micronm from the basal (serosal) membrane. Fast recording of the associated change in potential revealed an abrupt drop to -26 mV at a mean rate of 84 V/sec, followed by a further slow drop to a steady value of about -50 mV at a mean rate of 0.28 V/sec. The initial level of -26 mV may be regarded as the potential difference across the mucosal membrane. This conclusion was confirmed by mounting the microelectrode on a piezoelectric probe, which delivered 3 micron jabs in less than 0.5 msec. With this device in operation to prevent dimpling, the mean potential difference across the mucosal membrane was recorded as -29 mV. In all cases the potential across the basal membrane was recorded as -52 mV. Manual advance of the microelectrode tip within the cytoplasm yielded an intracellular potential gradient of 0.6 mV/micron. The same potential profile and membrane potentials were demonstrated on penetrating the epithelium from the serosal side, and measurements with multibarrelled electrodes whose tips were staggered in depth gave roughly the same internal potential gradient. The resistivity of the cytoplasm was determined by a triple-barrelled microelectrode, and varied from 10 times that of Necturus saline at the mucosal end of the cell to 4 times in the middle and 6 times at the serosal end.

Animals↗
PubMed1978

Intracellular gradients of ion activities in the epithelial cells of the Necturus gallbladder recorded with ion-selective microelectrodes.

In Necturus gallbladder epithelial cells the intracellular electrical potential, as recorded with microelectrodes, varied from -28 mV in the mucosal end to about -50 mV in the serosal end of the transporting cell. The Na+ activity varied concurrently from about 39 mM to between 8 and 19 mM. Thus, within the cell both the recorded electrical and chemical gradients caused Na+ to move towards the serosal end. Serosal addition of ouabain (5 X 10(-4) M) caused the intracellular Na+ activity to attain electrochemical equilibrium within 30 min. However, the intracellular electrical potential gradient was only slowly affected. In cells from animals stored at 5 degrees C, the Cl- activity varied from about 55 mM in the mucosal end to 28 mM in the serosal end, and the K+ activity from 50 mM to between 95 and 131 mM. Both ions were close to electrochemical equilibrium within the cytoplasm but were too concentrated to be in equilibrium with the mucosal solution. Bubbling CO2 through the mucosal solution caused the intracellular gradients to vanish. When Na+ in the bathing solutions was exchanged for K+, the intracellular electrical potential became roughly constant at about -5 mV. The Cl- activity became constant in 65 mM, and the K+ activity became constant at 109 mM, both close to equilibrium with the mucosal solution. The Na+ activity was reduced to about 1 mM. The ratio of cytoplasmic resistivities between cells bathed in K+-rich saline to cells bathed in Na+-rich saline was measured by means of triple-barreled electrodes and compared to the same ratio as assessed from the activity measurements. The two values were equal only if one assumes the mobility of Na+ inside the cell to be less than 1/10 of the mobility of K+ or Cl-. The same conclusion was reached by comparing the intracellular Na+ flux calculated from the gradient of electrochemical potential to that flux assess from the net solute absorption. Animals kept at 15 degrees C had lower intracellular Na+ activities, higher Cl- and K+ activities, and higher rates of absorption than animals stored at 5 degrees C. Finally, the degree to which the intracellularly recorded electrical and chemical potentials could reflect an electrode artefact is discussed.

Animals↗
PubMed1979

Triaminopyrimidinium (TAP+) blocks luminal membrane K conductance in Necturus gallbladder epithelium.

The effect of triaminopyrimidinium (TAP+) on the apical membrane of necturus gallbladder epithelial cells was investigated with intracellular microelectrode techniques. TAP+, added to the mucosal bathing solution only, produced the following effects (all rapid and reversible): (i) cell depolarization, (ii) increase of apical membrane resistance, and (iii) decrease of the apical membrane potential change produced by K for Na substitution on the mucosal side. These results can be explained by a decrease of apical membrane K conductance. The paracellular effects of TAP+ were similar to the ones previously described by Moreno (J.H. Moreno, 1974; Nature (London) 251:150; J.H. Moreno, 1975. J. Gen. Physiol. 66:97). These results indicate that the change of transepithelial potential produced by TAP+ cannot be ascribed solely to its effect on the paracellular pathway.

Animals↗