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PubMed1978

Effects of amphotericin b on the electrical properties of Necturus gallbladder: intracellular microelectrode studies.

Intracellular microelectrode techniques were employed to study the mechanism by which amphotericin B induces a transient mucosa-negative transepithelial potential (deltaVms) in the gallbladder of Necturus. When the tissue was incubated in standard Na-Ringer's solution, the antibiotic reduced the apical membrane potential by about 40 mV, and the basolateral membrane potential by about 35 mV, whereas the transepithelial potential increased by about 5 mV. The electrical resistance of the apical membrane fell by 83%, and that of the basolateral membrane by 40%; the paracellular resistance remained unchanged. Circuit analysis indicated that the equivalent electromotive forces of the apical and basolateral membranes fell by 35 and 11 mV, respectively. Changes in potentials and resistances produced by ionic substitutions in the mucosal bathing medium showed that amphotericin B produces a nonselective increase in apical membrane small monovalent cation conductance (K, Na, Li). In the presence of Na-Ringer's on the mucosal side, this resulted in a reduction of the K permselectivity of the membrane, and thus in a fall of its equivalent emf. During short term exposure to amphotericin B, PNa/PCl across the paracellular pathway did not change significantly, whereas PK/PNa doubled. These results indicate that deltaVms is due to an increase of gNa across the luminal membranes of the epithelial cells (Cremaschi et al., 1977. J. Membrane Biol. 34:55); the data do not support the alternative hypothesis (Rose & Nahrwold, 1976. J. Membrane Biol 29:1) that deltaVms results from a reduction in shunt PNa/PCl acting in combination with a rheogenic basolateral Na pump.

Amphotericin B↗
PubMed1977

Mechanisms of voltage transients during current clamp in Necturus gallbladder.

Microelectrode techniques were employed to study the mechanisms of the transepithelial voltage transients (deltaVms) observed during transmural current clamps in the isolated Necturus gallbladder. The results indicate that: a) part of deltaVms is due to a transepithelial resistance change (deltaRt), and part to a tissue emf change. b) deltaRt is entirely caused by changes of the resistance of the paracellular pathway. At all current densities employed, the measured changes are probably due to changes in both fluid conductivity and width of the lateral intercellular spaces. At high currents, in addition to the effects on the lateral spaces, the resistance of other elements of the pathway (probably the limiting junction) drops, regardless of the direction of the current. c) The magnitude and polarity of the deltaRt-independent transepithelial and cell membrane potential transients indicate that the largest emf change takes place at the basolateral membrane (deltaEb), with smaller changes at the luminal membrane (deltaEa) and the paracellular (shunt) pathway (deltaEs). It is shown that two-thirds of the transient are caused by deltaEs, and one-third by delta(Eb--Ea). deltaEs can be explained by a diffusion potential generated by a current-dependent NaCl concentration gradient across the tissue. deltaEa and deltaEb are caused by [K] changes, mainly at the unstirred layer in contact with the basolateral membrane.

Animals↗
PubMed1978

The effect of a disulfonic acid stilbene on proximal cell membrane potential in Necturus kidney.

The effects of 0.5 mM 4-acetamido-4'-isothiocyano-stilbene-2,2' disulfonic acid on the electrical properties of the peritubular membrane were studied in the proximal tubule of the perfused Necturus kidney. The addition of stilbene isothiocyanate disulfonic acid in peritubular perfusate resulted in an average 4.5 mV hyperpolarization with no detectable changes of peritubular membrane input conductance. The depolarization elicited by high-K media was enhanced by 18% in the presence of stilbene isothiocyanate disulfonic acid, an observation indicating that the inhibitor increased the contribution of potassium to membrane potential, presumably by decreasing anionic permeabilities. The hyperpolarizing effect of stilbene isothiocyanate disulfonic acid was abolished when peritubular bicarbonate was removed from the medium and isoosmotically replaced by chloride. These data suggest that (a) intracellular bicarbonate activity is higher than that predicted from passive distribution, (b) stilbene isothiocyanate disulfonic acid decreases P HCO3, thus hyperpolarizing the membrane, (c) chloride distribution appears to be passive when bicarbonate is removed from the peritubular perfusate. The state of Cl distribution when extracellular bicarbonate is at physiologic concentration cannot be assessed from the present data.

Animals↗
PubMed1978

Micropuncture studies of the transport of individual amino acids by the Necturus proximal tubule.

Absorption of amino acids by the necturus proximal tubules was measured under free-flow conditions The coexistence of proximal tubular amino acid influx was determined by infusing saline into tubular lumens by the stopped-flow microperfusion technique. Under free-flow conditions, fractional absorption of individual amino acids ranged from 0.30 +/- 0.18 (glutamic acid) to 0.96 +/- 0.02 (proline), with 14 of 19 values greater than 0.75. The transport avidity for a given amino acid bore no relationship to its molecular weight, transport class, or plasma concentration. The values obtained for tubular fluid/plasma (TF/P) were very comparable to those reported for the rat. In stopped-flow microperfusion experiments, samples of isotonic saline residing in tubule lumens for 20 min were found to contain all the amino acids present in plasma (filtrate). The concentrations of all except the acidic anionic pair, glutamic acid and aspartic acid, were remarkably similar to those obtained by collection of end proximal samples in free-flow studies. The very high concentrations of the acidic amino acids may reflect their passive distribution across the luminal cell membrane, active absorption having been impaired by the absence of some substance normally present in glomerular filtrate.

Amino Acids↗
PubMed1980

Organic substrate effects on and heterogeneity of Necturus proximal tubule function.

The effect of organic substrates such as lactate, alanine, glutamine, glutamate, lysine, and butyrate is compared with that of glucose, and the role of tubular heterogeneity is assessed in Necturus proximal tubule. Fluid absorption (Jv) is enhanced 34% by the presence of all substrates together in the tubular lumen. Addition of glucose to the peritubular perfusion fluid does not increase Jv significantly, whereas the other substrates augment Jv by 181%. Transepithelial potential difference (V3) and peritubular membrane potential difference (V1) are unaffected by these organic substrates. Transepithelial chloride to sodium transference number ratios (tCl/tNa) and transepithelial specific resistance (Rm) are higher in the presence of substrates, possibly because of effects on paracellular conductance. Organic solutes could influence fluid absorption by increasing entry of sodium across the luminal cell membrane, by increasing energy supply to the active transport mechanism, or by decreasing paracellular conductance. Early and late straight segments of the proximal tubule do not differ significantly in V3, V1, and transepithelial tCl/tNa. Early convoluted segments have a higher Jv than do late straight proximal segments, but they have a lower transepithelial specific resistance. We have concluded that net fluid absorption and transepithelial ionic conductance correlates with the supply of certain organic solutes and with specific localization along the proximal tubule.

Alanine↗
PubMed1968

Organization and activity in the pre- and postovulatory follicle of Necturus maculosus.

The established follicle envelope of Necturus maculosus consists of a layer of follicle cells (granulosa) surrounding the developing oocyte, a layer of theca comprised of connective tissue cells, fibers, and matrix, and a layer of serosal cells. The changes in shape and fine structure of these layers during differentiation accompanying oogenesis are described. The cells and capillaries of the follicle envelope are engaged in an extensive pinocytotic activity, the details of which are described. We used cytochemical techniques to analyze the activity of the follicle envelope with respect to lipid accumulation and alkaline phosphatase activity. Radioautographic results indicate that cells of the follicle envelope are capable of incorporating tritium-labeled uridine and amino acids at certain times during oocyte growth. A comparative analysis was made of the soluble proteins in follicle envelopes isolated from immature oocytes and of those in follicle envelopes isolated from nearly mature oocytes and in postovulatory follicles. After the oocyte is ovulated, the cells of the follicle envelope are converted into a postovulatory follicle. The cells of the postovulatory follicle undergo further differentiation resulting in their becoming actively engaged in the formation of a secretion, the details of which are described at the electron microscope level. Analysis of the postovulatory follicle by thin-layer chromatography and cytochemistry demonstrated the presence of a wide variety of lipid substances and the possible presence of steroid. That the postovulatory follicle may be engaged in steroid biosynthesis is also suggested by studies involving the demonstration of 3 beta-hydroxysteroid dehydrogenase activity with cytochemical techniques applied to frozen sections and to soluble proteins separated by gel electrophoresis.

Animals↗
PubMed1976

Morphological changes in tight junctions of Necturus maculosus proximal tubules undergoing saline diuresis.

Tight junctions between epithelial cells are believed to control the paracellular diffusion of substances across epithelia. Epithelia in which tight junctions are poorly developed display a higher paracellular electrical conductance, while those with extensive tight junctions show lower conductance values. We described here a particular epithelium, that of the proximal tubules of the Necturus kidney, in which the development of the tight junctions varies in parallel with a change of paracellular electrical conductance. In control conditions, tight junctions between epithelial cells of the proximal tubules are more developed than in tubules undergoing saline diuresis, a situation which increases the conductance across the paracellular shunt pathway.

Animals↗
PubMed1972

Sodium flux in Necturus proximal tubule under voltage clamp.

Na transport and electrical properties of Necturus renal proximal tubules were analyzed, in vivo, by a voltage clamp method which utilizes an axial electrode in the tubule lumen for passage of current and simultaneous determination of net fluid (or Na) flux by the split droplet method. When the average spontaneous transepithelial potential difference of -8 mv (lumen negative) was reduced to zero by current passage, net Na flux doubled from a mean of 107 to 227 pmoles/cm(2) per sec. The relationship between flux and potential over the range -25 to +10 mv was nonlinear, with flux equilibrium at -15 mv and droplet expansion at more negative values. Calculated Na permeability at flux equilibrium was 7.0 x 10(-6) cm/sec. Voltage transients, similar to those caused by intraepithelial unstirred layers, were observed at the end of clamping periods. Tubular electrical resistance measured by brief square or triangle wave pulses (<100 msec) averaged 43 ohm cm(2). The epithelial current-voltage relationship was linear over the range -100 to +100 mv, but displayed marked hysteresis during low frequency (<0.04 Hz) triangle wave clamps. The low transepithelial resistance and large opposing unidirectional ion fluxes suggest that passive ionic movements occur across extracellular shunt pathways, while the voltage transients and current-voltage hysteresis are consistent with the development of a local osmotic gradient within epithelium.

Animals↗
PubMed1975

Models for coupling of salt and water transport; Proximal tubular reabsorption in Necturus kidney.

Models for coupling of salt and water transport are developed with two important assumptions appropriate for leaky epithelia. (a) The tight junction is permeable to both sale and water. (b) Active Na transport into the lateral speces is assumed to occur uniformly along the length of the channel. The proposed models deal specifically with the intraepithelial mechanism of proximal tubular resbsorption in the Necturus kidney although they have implications for epithelial transport in the gallbladder and small intestine as well. The first model (continuous version) is similar to the standing gradient model devised by Diamond and Bossert but used different boundary conditions. In contrast to Diamond and Bossert's model, the predicted concentration profiles are relatively flat with no sizable gradients along the interspace. The second model (compartment version) expands Curran's model of epithelial salt and water transport by including additional compartments and considering both electrical and chemical driving forces for individual Na and Cl ions as well as hydraulic and osmotic driving forces for water. In both models, ion and water fluxes are investigated as a function of the transport parameters. The behavior of the models is consistent with previously suggested mechanisms for the control of net transport, particularly during saline diuresis. Under all conditions the predicted ratio of net solute to solvent flux, or emergent concentration, deviates from exact isotonicity (except when the basement membrane has an appreciable salt reflection coefficient). However, the degree of hypertonicity may be small enough to be experimentally indistinguishable from isotonic transport.

Animals↗
PubMed1979

Fluid transport and the dimensions of cells and interspaces of living Necturus gallbladder.

The volume of the cells and lateral intercellular spaces were measured in living Necturus gallbladder epithelium. Under control conditions, the volume of the lateral spaces was 9% of the cell volume. Replacement of mucosal NaCl by sucrose or tetramethylammonium chloride (TMACl) caused intercellular spaces to collapse. During mucosal NaCl replacement, cell volume decreased to 79% of its control value. When NaCl was reintroduced into the mucosal bath, the intercellular spaces reopened and the cells returned to control volume. The NaCl active transport rate, calculated from the rate of cell volume decrease, was 266 pM/cm2.s, close to the observed rate of transepithelial salt transport. It was calculated from the decrease in cell volume that all of the intracellular NaCl was transported out of the cell during removal of mucosal NaCl. The flux of salt across the apical membrane, calculated from the rate of cell volume increase upon reintroducing mucosal NaCl, was 209 pM/cm2.s, in good agreement with estimates by other methods. The electrical resistance of the tight junctions was estimated to be 83.9% of the total tissue resistance in control conditions, suggesting that the lateral intercellular spaces normally offer only a small resistance to electrolyte movement.

Animals↗
PubMed1979

Effects of ouabain on fluid transport and electrical properties of Necturus gallbladder. Evidence in favor of a neutral basolateral sodium transport mechanism.

Net fluid transport (Jv) and electrical properties of the cell membranes and paracellular pathway of Necturus gallbladder epithelium were studied before and after the addition of ouabain (10(-4) M) to the serosal bathing medium. The glycoside inhibited Jv by 70% in 15 min and by 100% in 30 min. In contrast, the potentials across both cell membranes did not decrease significantly until 20 min of exposure to ouabain. At 30 min, the basolateral membrane potential (Vcs) fell only by ca 7 mV. If basolateral Na transport were electrogenic, with a coupling ratio (Na:K) of 3:2, the reductions of Vcs at 15 and 30 min should be 12--15 and 17--21 mV, respectively. Thus, we conclude that the mechanism of Na transport from the cells to the serosal bathing solution is not electrogenic under normal transport conditions. The slow depolarization observed in ouabain is caused by a fall of intracellular K concentration, and by a decrease in basolateral cell membrane K permeability. Prolonged exposure to ouabain results also in an increase in paracellular K selectivity, with no change of P Na/P Cl.

Animals↗
PubMed1979

Sodium channels in axons and glial cells of the optic nerve of Necturus maculosa.

Experiments investigating both the binding of radioactively labelled saxitoxin (STX) and the electrophysiological response to drugs that increase the sodium permeability of excitable membranes were conducted in an effort to detect sodium channels in glial cells of the optic nerve of Necturus maculosa, the mudpuppy. Glial cells in nerves from chronically enucleated animals, which lack optic nerve axons, show no saturable uptake of STX whereas a saturable uptake is clearly present in normal optic nerves. The normal nerve is depolarized by aconitine, batrachotoxin, and veratridine (10(-6)-10(-5) M), whereas the all-glial preparation is only depolarized by veratridine and at concentrations greater than 10(-3) M. Unlike the depolarization caused by veratridine in normal nerves, the response in the all-glial tissue is not blocked by tetrodotoxin nor enhanced by scorpion venom (Leiurus quinquestriatus). In glial cells of the normal nerve, where axons are also present, the addition of 10(-5) M veratridine does lead to a transient depolarization; however, it is much briefer than the axonal response to veratridine in this same tissue. This glial response to veratridine could be caused by the efflux of K+ from the drug-depolarized axons, and is similar to the glial response to extracellular K+ accumulation resulting from action potentials in the axon.

Animals↗
PubMed1980

Neurons, potassium, and glia in proximal retina of Necturus.

Light-evoked K+ flux and intracellular Müller (glial) cell and on/off-neuron responses were recorded from the proximal retina of Necturus in eyecups from which the vitreous was not drained. On/off-responses, probably arising from amacrine cells, showed an initial transient and a sustained component that always exhibited surround antagonism. Müller cell responses were small but otherwise similar to those recorded in eyecups drained of vitreous. The proximal K+ increase and Müller cell responses had identical decay times, and on some occasions the latency and rise time of the K+ increase nearly matched Müller cell responses, indicating that the recorded K+ responses were not always appreciably degraded by electrode "dead space." The spatiotemporal distribution of the K+ increase showed that both diffusion and active reuptake play important roles in K+ clearance. The relationship between on/off-neuron responses and the K+ increase was modelled by assuming that (a) K+ release is positively related to the instantaneous amplitude of the neural response, and (b) K+ accumulating in extracellular space is cleared via mechanisms with approximately exponential time-courses. These two processes were approximated by low-pass filtering the on/off-neuron responses, resulting in modelled responses that match the wave form and time-course of the K+ increase and behave quantitatively like the K+ increase to changes in stimulus intensity and diameter. Thus, on/off-neurons are probably a primary source of the proximal light-evoked K+ increase that depolarizes glial cells to generate the M-wave.

Animals↗
PubMed1972

Calcium dependence of ciliary activity in the oviduct of the salamander Necturus.

1. Ciliary activity in the oviduct of the mud puppy Necturus maculosus was monitored by a photometric technique in normal, decalcified, and Triton X-extracted preparations to investigate the regulatory role of calcium ions.2. The frequency of ciliary beating in the isolated tissue ranged from 0 to 12 beats/sec. The frequency in any one group of cells underwent large cyclical variations with periods of 2 min or more.3. Frequency of beating reached a maximum and remained at a plateau upon addition of 1 mM caffeine. Beating temporarily ceased upon removal of the caffeine.4. Ionophoretic injection of calcium ions into an active cell bathed in Ringer solution produced an increased rate of beating. In cells rendered quiescent by prior decalcification with EGTA, injected calcium rapidly restored ciliary activity.5. Epithelia extracted in Triton X-100 were inactive until reactivated by addition of ATP and magnesium ions. The frequency of beating increased between 0.1 and 4.0 mM ATP in 1 mM magnesium, and between 0.2 and 2.5 mM magnesium in 1 mM ATP.6. The frequency of beating in the ATP-reactivated, Triton-extracted tissue was independent of the calcium ion concentration.7. Cells inactivated by decalcification were reactivated by injection of ATP or by extracellular ATP levels as low as 3 x 10(-8)M.8. It is concluded that the frequency of beating depends directly on the concentration of the available energy source, presumably ATP, and that an indirect dependence of beating frequency on calcium concentration in the living tissue results from rate-limiting effects of intracellular calcium on metabolic steps in pathways leading to ATP synthesis.

Adenosine Triphosphate↗
PubMed1973

Relationship between tubular net sodium reabsorption and peritubular potassium uptake in the perfused Necturus kidney.

1. K influx from peritubular space into renal tubular cells, varphi(i) (K), was measured in doubly perfused Necturus kidneys by studying tissue uptake of (42)K added exclusively to the portal circulation. Concomitantly, net tubular Na reabsorption, varphi(n) (Na), was measured by clearance techniques. varphi(n) (Na) and varphi(i) (K) were varied widely by replacing solutions of physiological composition (controls) with solutions containing high K, low K, low Na, cyclamate instead of Cl, ouabain (10(-7)-10(-4)M) or ethacrynic acid (10(-5)-10(-4)M).2. The ratio of varphi(n) (Na) to varphi(i) (K) was found to vary with the experimental conditions, the control value of about 2 was maintained over a threefold variation in absolute Na reabsorption. This ratio increased with low K or ouabain to values near 4. With high K, ethacrynic acid, low Na or cyclamate the relationship was one or lower. Thus, net Na reabsorption can be uncoupled from peritubular K influx.3. These results can be best explained if there are two Na pumps working in parallel: pump A transporting Na (with Cl) and pump B, a Na-for-K-exchange pump. The ratio of Na efflux to K influx could approach infinity if only pump A works (if B is inhibited) and could approach one if only B works. It should vary between these limits in controls when both pumps are active, or when neither of the two pumps is completely inhibited.4. Alternatively, the experimental findings could be explained by a Na pump with a coupling ratio that varies within two extreme values, from high Na-K ratios (with Na reabsorption at, or near, control values but with very low K influx values) to low ratios (with normal K influx values but with low Na reabsorption values).

Absorption↗
PubMed1973

Biionic potentials in the proximal tubule of Necturus kidney.

1. Biionic potentials were studied in the proximal tubule of the doubly perfused Necturus kidney and subsequently analysed by means of an equivalent electrical circuit.2. Luminal membrane resistance was found to be at least 3 times greater than peritubular membrane resistance.3. Potassium contribution to peritubular membrane conductance amounts to at least 75%. Replacement of chloride in peritubular circulation by benzene sulphonate or acetyl glycinate hyperpolarized peritubular membrane.4. The peritubular membrane is more permeable to choline than to sodium. Indirect evidence suggests that the opposite may apply at the luminal border.5. The shunt pathway discriminates poorly, if at all, between sodium, potassium and choline, in short term experiments.6. Chloride permeability across the shunt pathway is about three times as great as combined cationic permeabilities.

Animals↗
PubMed1974

Sensitization and centre-surround antagonism in Necturus retina.

1. The impulse discharge of ganglion cells and the proximal negative response were recorded with extracellular micro-electrodes in Necturus retina and spatial influences of background illumination studied.2. When a steady background of constant illuminance was extended in diameter from 0.25 to 1 mm, the response to a small concentrically placed test flash was enhanced (sensitization).3. This sensitization was tonic, showed marked spatial summation, was also found by surrounding a central background with an annulus, and when quantified by threshold measurements, closely resembled the sensitization effect found psychophysically in human vision.4. Sensitization was prominent in intracellular recordings from bipolar cells and usually apparent in horizontal cells. In bipolar cells, a background change which produced sensitization evoked a large but predominantly transient potential whose polarity was opposite to that evoked by a central flash.5. The tonicity and large spatial extent of the sensitization effect strongly suggest that it is mediated by horizontal cells. They might do this by either acting upon receptors, bipolar cells, or both.

Animals↗
PubMed1977

Electrophysiological study of the antiluminal membrane in the proximal tubule of Necturus: effect of inorganic anions and SCN-.

1. A study has been made of the effects of anionic substitutions on the electrical potential difference (p.d.) and conductance characteristics of the antiluminal (peritubular) membrane of the proximal tubule of Necturus kidney. The tubular lumina were filled with oil in order to minimize potential and conductance contributions from luminal membrane and from paracellular shunt pathway.2. Isosmotic substitutions, [A](o) for [Cl](o), produced the following average changes in membrane p.d. (mV): F(-) +1.7, BrO(3) (-) +0.1, Br(-) -4.5, ClO(3) (-) -5.2, I(-) -7.9, NO(3) (-) -12.1, ClO(4) (-) -17.8, SCN(-) -25.3.3. The amplitude of the depolarization caused by increase in K concentration (K-depolarization) in the peritubular perfusate was found to increase during perfusion of the tissue with ClO(4) (-) (by 78%), SCN(-) (45%), I(-) (23%), NO(3) (-) (20%), Br(-) (16%); it decreased with F(-) (by 17%).4. Comparison of membrane p.d. at peak K-depolarization in the control state (during KCl perfusion) with that obtained in the experimental state (during KA perfusion) was found to be more reliable than determination of bi-ionic potentials as a qualitative estimate of the permeabilities of the various anions (P(A)) relative to that of chloride (P(Cl)).5. Study of both peak K-depolarization p.d. and bi-ionic potentials yielded the following sequence for halide anion permeabilities: P(F) > P(Cl) > P(Br) > P(I). The peritubular membrane was found to be substantially more permeable to NO(3) (-), ClO(4) (-) and SCN(-) than to Cl(-).6. The sequence of membrane conductances during anionic substitutions was Cl(-) approximately BrO(3) (-) < Br(-) </= ClO(3) (-) < I(-) approximately F(-) < NO(3) (-) < ClO(4) (-) < SCN(-).7. From the changes in p.d. induced by K-depolarization, the absolute values of p.d. at peak K-depolarization and from the changes in membrane conductance induced by anionic substitutions, it may be inferred that Br(-), I(-), NO(3) (-), ClO(4) (-) and SCN(-) all increase P(K); and that F(-) increases P(Na) (though a smaller increase in P(K) cannot be excluded).

Animals↗