Electrophysiological properties of amphibian late distal tubule in vivo

1988 ◽  
Vol 255 (1) ◽  
pp. F158-F166
Author(s):  
G. Planelles ◽  
T. Anagnostopoulos
Keyword(s):  
Cell Membrane ◽  
Apical Cell ◽  
Electrical Coupling ◽  
Distal Tubule ◽  
Ion Concentration ◽  
Transference Numbers ◽  
Apical Cell Membrane ◽  
Electrophysiological Properties ◽  
Concentration Changes

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+.

scholarly journals Relationship between cell volume and ion transport in the early distal tubule of the Amphiuma kidney.

1985 ◽  
Vol 86 (1) ◽  
pp. 31-58 ◽  
Author(s):  
W B Guggino ◽  
H Oberleithner ◽  
G Giebisch
Keyword(s):  
Cell Membrane ◽  
Cell Volume ◽  
Cell Membranes ◽  
Apical Cell ◽  
Distal Tubule ◽  
Cell Swelling ◽  
Osmotic Swelling ◽  
Apical Cell Membrane ◽  
Basolateral Cell Membrane ◽  
Tubule Cells

The roles of apical and basolateral transport mechanisms in the regulation of cell volume and the hydraulic water permeabilities (Lp) of the individual cell membranes of the Amphiuma early distal tubule (diluting segment) were evaluated using video and optical techniques as well as conventional and Cl-sensitive microelectrodes. The Lp of the apical cell membrane calculated per square centimeter of tubule is less than 3% that of the basolateral cell membrane. Calculated per square centimeter of membrane, the Lp of the apical cell membrane is less than 40% that of the basolateral cell membrane. Thus, two factors are responsible for the asymmetry in the Lp of the early distal tubule: an intrinsic difference in the Lp per square centimeter of membrane area, and a difference in the surface areas of the apical and basolateral cell membranes. Early distal tubule cells do not regulate volume after a reduction in bath osmolality. This cell swelling occurs without a change in the intracellular Cl content or the basolateral cell membrane potential. In contrast, reducing the osmolality of the basolateral solution in the presence of luminal furosemide diminishes the magnitude of the increase in cell volume to a value below that predicted from the change in osmolality. This osmotic swelling is associated with a reduction in the intracellular Cl content. Hence, early distal tubule cells can lose solute in response to osmotic swelling, but only after the apical Na/K/Cl transporter is blocked. Inhibition of basolateral Na/K ATPase with ouabain results in severe cell swelling. This swelling in response to ouabain can be inhibited by the prior application of furosemide, which suggests that the swelling is due to the continued entry of solutes, primarily through the apical cotransport pathway.

Ionic conductive properties and electrophysiology of the rabbit cortical collecting tubule

1982 ◽  
Vol 243 (1) ◽  
pp. F81-F95 ◽  
Author(s):  
R. G. O'Neil ◽  
E. L. Boulpaep
Keyword(s):  
Cell Membrane ◽  
Tight Junction ◽  
Apical Cell ◽  
Apical Cell Membrane ◽  
Electrophysiological Properties ◽  
Basolateral Cell Membrane ◽  
Collecting Tubule ◽  
Conductive Properties ◽  
K Permeability ◽  
Cortical Collecting Tubule

The Na, K, and Cl conductive properties and the electrophysiological variability of the rabbit isolated cortical collecting tubule were assessed by evaluating the effect of single-ion substitutions on the transepithelial potential difference, Vte, and the transepithelial conductance, Gte. The Na permeability (and conductance) of the tight junction and basolateral cell membrane appeared to be low. However, a significant but variable amiloride-sensitive Na conductance was identified at the apical cell membrane. Although this Na conductance accounts for less than 10% of the Gte, variations in this conductance caused major alterations in the active transepithelial Na current and the Vte. A highly variable K permeability (and conductance) was also identified at the apical cell border and may account for some of the variability in Vte and Gte. This probably provides a pathway for K secretion from cell to lumen. The K permeability of the tight junction and basolateral cell membrane appeared to be relatively low. In contrast, the Cl permeability (and conductance) of the tight junction, and perhaps of the basolateral cell membrane, appeared to be high but variable and to account for the major fraction of the Gte and its variability. It is concluded that variations in the Na and K conductance of the apical cell membrane and the Cl conductance of the tight junction and basolateral cell membrane predominantly account for the variations in the electrophysiological properties of the cortical collecting tubule.

scholarly journals UNSTIMULATED SECRETION OF PROTEIN FROM RAT EXOCRINE PANCREAS CELLS

1972 ◽  
Vol 52 (1) ◽  
pp. 147-158 ◽  
Author(s):  
M. F. Kramer ◽  
C. Poort
Keyword(s):  
Protein Synthesis ◽  
Cell Membrane ◽  
Secretory Granules ◽  
Apical Cell ◽  
Secretory Protein ◽  
Secretory Process ◽  
Tissue Slices ◽  
Apical Cell Membrane

Our earlier work demonstrated that the rate of protein synthesis in the exocrine cells of the rat pancreas is constant in different physiological states, including prolonged fasting. In this study we have followed the fate of the protein in the pancreatic cells of the fasting animal in vivo as well as in vitro. The data were obtained by quantitative radioautography and by biochemical determinations. In nonanesthesized, fasting rats, without cannulated pancreatic duct, some 80% of the proteins synthesized at a given time leaves the cell within 12 hr by way of secretion, intracellular breakdown not being important. Two mechanisms of fasting secretion exist. The first, starting at a slow rate after 20 min, is inferred to result from fortuitous contacts of young secretory granules with the apical cell membrane. The rate of secretion is the same in vivo as in vitro, at least during the first 4 hr after pulse labeling. Within 7 hr about 20% of the total amount of newly synthesized protein has left the cell. The second mechanism consists of an orderly movement of the mass of secretory granules towards the apical cell membrane as caused by the continuous assembly of new granules. The granules that come into contact with the cell membrane are discharged. It takes about 7–12 hr for secretory protein transported in this way to reach the cell membrane. The addition of new secretory granules to those present is essential for the second mechanism, for the blockade of protein synthesis by cycloheximide decreases the rate of this phase of secretion without interfering with the secretory process proper. Atropin does not inhibit the fasting secretion in vitro, nor does extensive washing of the tissue slices, excluding possible secretagogues as important factors in fasting secretion.

Fine structure of the rectal papillae of the oriental fruuit fly, Dacus dorsalis Hendel (Tephritidae, Diptera Insecta)

1990 ◽  
Vol 48 (3) ◽  
pp. 498-499
Author(s):  
Len Wen-Yung ◽  
Mei-Jung Lin
Keyword(s):  
Fine Structure ◽  
Cell Membrane ◽  
Intercellular Space ◽  
Anterior Part ◽  
Apical Cell ◽  
Posterior Part ◽  
Apical Cell Membrane ◽  
Dacus Dorsalis ◽  
Radial Cell ◽  
Circular Base

Four cone-shaped rectal papillae locate at the anterior part of the rectum in Dacus dorsalis fly. The circular base of the papilla protrudes into the haemolymph (Fig. 1,2) and the rest cone-shaped tip (Fig. 2) inserts in the rectal lumen. The base is surrounded with the cuticle (Fig. 5). The internal structure of the rectal papilla (Fig. 3) comprises of the cortex with the columnar epithelial cells and a rod-shaped medulla. Between them, there is the infundibular space and many trabeculae connect each other. Several tracheae insert into the papilla through the top of the medulla, then run into the cortical epithelium and locate in the intercellular space. The intercellular sinuses distribute in the posterior part of the rectal papilla.The cortex of the base divides into about thirty segments. Between segments there is a radial cell (Fig. 4). Under the cuticle, the apical cell membrane of the cortical epithelium is folded into a regular border of leaflets (Fig. 5).

Mineralocorticoid regulation of apical cell membrane Na+ and K+ transport of the cortical collecting duct

1985 ◽  
Vol 248 (6) ◽  
pp. F858-F868 ◽  
Author(s):  
S. C. Sansom ◽  
R. G. O'Neil
Keyword(s):  
Cell Membrane ◽  
Tight Junction ◽  
Apical Membrane ◽  
Collecting Duct ◽  
Apical Cell ◽  
Cortical Collecting Duct ◽  
Apical Cell Membrane ◽  
K Secretion ◽  
Junction Conductance ◽  
K Transport

The effects of mineralocorticoid (DOCA) treatment of rabbits on the Na+ and K+ transport properties of the cortical collecting duct apical cell membrane were assessed using microelectrode techniques. Applying standard cable techniques and equivalent circuit analysis to the isolated perfused tubule, the apical cell membrane K+ and Na+ currents and conductances could be estimated from the selective effects of the K+ channel blocker Ba2+ and the Na+ channel blocker amiloride on the apical membrane; amiloride treatment was observed also to decrease the tight junction conductance by an average of 10%. After 1 day of DOCA treatment, the Na+ conductance and current (Na+ influx) of the apical cell membrane doubled and remained elevated with prolonged treatment for up to 2 wk. The apical cell membrane K+ conductance was not influenced after 1 day, although the K+ current (K+ secretion) increased significantly due to an increased driving force for K+ exit. After 4 days or more of DOCA treatment the K+ conductance doubled, resulting in a further modest stimulation in K+ secretion. After 2 wk of DOCA treatment the tight junction conductance decreased by near 30%, resulting in an additional hyperpolarization of the transepithelial voltage, thereby favoring K+ secretion. It is concluded that the acute effect (within 1 day) of mineralocorticoids on Na+ and K+ transport is an increase in the apical membrane Na+ conductance followed by delayed chronic alterations in the apical membrane K+ conductance and tight junction conductance, thereby resulting in a sustained increased capacity of the tubule to reabsorb Na+ and secrete K+.

Bovine pancreatic duct cells express cAMP- and Ca(2+)-activated apical membrane Cl- conductances

1997 ◽  
Vol 273 (1) ◽  
pp. G204-G216 ◽  
Author(s):  
L. al-Nakkash ◽  
C. U. Cotton
Keyword(s):  
Epithelial Cells ◽  
Cell Membrane ◽  
Pancreatic Duct ◽  
Apical Membrane ◽  
Apical Cell ◽  
Primary Cultures ◽  
Apical Cell Membrane ◽  
Anion Secretion ◽  
Duct Epithelium ◽  
Cl Permeability

Secretion of salt and water by the epithelial cells that line pancreatic ducts depends on activation of apical membrane Cl- conductance. In the present study, we characterized two types of Cl- conductances present in the apical cell membrane of bovine pancreatic duct epithelial cells. Primary cultures of bovine main pancreatic duct epithelium and an immortalized cell line (BPD1) derived from primary cultures were used. Elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) or Ca2+ in intact monolayers of duct epithelium induced sustained anion secretion. Agonist-induced changes in plasma membrane Cl- permeability were accessed by 36 Cl- efflux, whole cell current recording, and measurements of transepithelial Cl- current across permeabilized epithelial monolayers. Elevation of intracellular cAMP elicited a sustained increase in Cl- permeability, whereas elevation of intracellular Ca2+ induced only a transient increase in Cl- permeability. Ca(2+)- but not cAMP-induced increases in Cl- permeability were abolished by preincubation of cells with the Ca2+ buffer 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, tetra(acetoxymethyl) ester (BAPTA-AM). N-phenylanthranilic acid (DPC; 1 mM) and glibenclamide (100 microM), but not 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 500 microM), inhibited the cAMP-induced increase in Cl- permeability. In contrast, DPC and DIDS, but not glibenclamide, inhibited the Ca(2+)-induced increase in Cl- permeability. We conclude from these experiments that bovine pancreatic duct epithelial cells express at least two types of Cl- channels, cAMP and Ca2+ activated, in the apical cell membrane. Because the Ca(2+)-activated increase in Cl- permeability is transient, the extent to which this pathway contributes to sustained anion secretion by the ductal epithelium remains to be determined.

The collecting tubule of Amphiuma. I. Electrophysiological characterization

1987 ◽  
Vol 253 (6) ◽  
pp. F1263-F1272 ◽  
Author(s):  
M. Hunter ◽  
J. D. Horisberger ◽  
B. Stanton ◽  
G. Giebisch
Keyword(s):  
Cell Membrane ◽  
Cell Model ◽  
Basolateral Membrane ◽  
Apical Cell ◽  
Potassium Conductance ◽  
Sodium Reabsorption ◽  
Apical Cell Membrane ◽  
Cation Selectivity ◽  
Basolateral Cell Membrane ◽  
Collecting Tubules

Single collecting tubules of Amphiuma kidneys were perfused in vitro to characterize their electrophysiological properties. The lumen-negative potential (-24 mV) was abolished by amiloride in the lumen and by ouabain in the bath. Ion substitution experiments in the lumen demonstrated the presence of a large sodium conductance in the apical cell membrane, but no evidence was obtained for a significant potassium or chloride conductance. Ion substitutions in the bath solution and the depolarizing effect of barium on the basolateral membrane potential demonstrated the presence of a large potassium conductance in the basolateral cell membrane. Measurements of dilution potentials in amiloride-treated tubules revealed a modest cation selectivity of the paracellular pathway. These results support a cell model in which sodium reabsorption occurs by electrodiffusion across the apical cell membrane and active transport across the basolateral cell membrane. The absence of a detectable potassium conductance in the apical cell membrane suggests that secretion of this ion cannot take place by diffusion from cell to lumen.

Microelectrode assessment of chloride-conductive properties of cortical collecting duct

1984 ◽  
Vol 247 (2) ◽  
pp. F291-F302 ◽  
Author(s):  
S. C. Sansom ◽  
E. J. Weinman ◽  
R. G. O'Neil
Keyword(s):  
Cell Membrane ◽  
Tight Junction ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Apical Cell ◽  
Membrane Conductance ◽  
Cortical Collecting Duct ◽  
Apical Cell Membrane ◽  
Conductive Properties ◽  
Chloride Activity

The chloride-conductive properties of the isolated rabbit cortical collecting duct were assessed with microelectrode techniques. The transepithelial, apical, and basolateral membrane potential differences, Vte, Va, and Vb, respectively, were monitored continuously along with periodic measurements of the transepithelial conductance, Gte, and fractional resistance, fRa (ratio of apical to apical plus basolateral membrane resistance). Active transport was eliminated in all experiments by luminal addition of 50 microM amiloride in HCO3-free solutions. Upon reducing the chloride activity in the bath (gluconate replacement), there was a marked depolarization of Vb and decrease in Gte and fRa, demonstrating a major dependence of the basolateral membrane conductance on the bath chloride activity. However, a significant K+ conductance at that barrier was also apparent since raising the bath K+ concentration caused an increase in Gte and fRa and depolarization of Vb. Lowering the chloride activity of the perfusate caused a consistent decrease of Gte but not of fRa, effects consistent with a high C1- conductance of the tight junction and little, if any, apical membrane C1- conductance. By use of the C1- -dependent conductances, the C1- permeabilities at equilibrium were estimated to be near 1.0 X 10(-5) cm X s-1 for the tight junction, PtiC1, and 5 X 10(-5) cm X s-1 for the basolateral cell membrane, PbC1. It is concluded that the paracellular pathway provides a major route for transepithelial C1- transport. Furthermore, since the isotopically measured C1- permeability is severalfold greater than PtiC1, a significant transcellular flux of C1- must exist, implicating a neutral exchange mechanism at the apical cell membrane in series with the high basolateral membrane C1- conductance.

Local mechanisms of phase-dependent postsynaptic modifications of NMDA-induced oscillations in the abducens motoneurons: a simulation study

1996 ◽  
Vol 76 (2) ◽  
pp. 1015-1024 ◽  
Author(s):  
I. L. Kopysova ◽  
S. M. Korogod ◽  
J. Durand ◽  
S. Tyc-Dumont
Keyword(s):  
Synaptic Input ◽  
Pattern Generation ◽  
Ion Concentration ◽  
Extracellular Potassium ◽  
Pump System ◽  
Voltage Gated ◽  
Ion Concentrations ◽  
Concentration Changes ◽  
Transmembrane Currents

1. In vivo experiments have shown that extracellular microelectrophoretic application of N-methyl-D-aspartate (NMDA) induced oscillatory plateau potentials with bursts of action potentials in rat abducens motoneurons. The period of these slow NMDA oscillations could be altered by single trigeminal non-NMDA excitatory input delivered at low frequency during the NMDA oscillations. 2. A resetting of the oscillations was observed depending on the phase of slow oscillatory cycle during which the trigeminal excitation occurred. 3. We investigated local mechanisms responsible for the phase-dependent modifications of NMDA oscillations, including contributions of voltage and concentration transients, in the mathematical model of the isopotential membrane compartment equipped with voltage-gated Na+, K+, and Ca2+ channels, with Ca2+-dependent K+ channels, and with ligand-gated NMDA and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor channels. The faithful model was constructed with the use of models described earlier, which were modified by increasing time constants of kinetic variables of all voltage-gated conductances and by including coupled dynamics of voltages and ion concentrations. The changes in ion concentrations were produced near the membrane by transmembrane currents and removal mechanisms (pumps, diffusion). 4. This work focuses on local arrangement of voltage- and ligand-gated conductances and on local ion concentration changes in two separate pools: the postsynaptic pool of AMPA receptors and the extrasynaptic pool. In terms of the electrotonic and diffusional length constants, these pools were electrotonically close but diffusionally remote. 5. It was found that the effect of resetting can be produced by a local interaction between plateau and spike-generating conductances and glutamate receptors. 6. In vivo phase-dependent interactions between NMDA oscillations and AMPA synaptic input were reproduced by the local model only when changes in intracellular sodium and extracellular potassium concentrations were taken into account and the mechanisms of ion removal from postsynaptic pools had slower kinetics than the fast pump system operating in the extracellular pool. 7. Postsynaptic changes in ion concentrations of Na+ and K+ in intra- and extracellular layers near the membrane shift of Nernst equilibrium potentials for these ions depending on the phase of activation of synaptic input. Thus Na+ and k+ components of all transmembrane currents involved in the pattern generation are differently affected by synaptic action during the oscillations. We conclude that slow postsynaptic changes in ion concentrations near the membrane play a key role in the resetting of the NMDA oscillations.

Conductive properties of the rabbit outer medullary collecting duct: inner stripe

1985 ◽  
Vol 248 (4) ◽  
pp. F500-F506 ◽  
Author(s):  
B. M. Koeppen
Keyword(s):  
Cell Membrane ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Apical Cell ◽  
Rabbit Kidney ◽  
Apical Cell Membrane ◽  
Basolateral Cell Membrane ◽  
Medullary Collecting Duct ◽  
Conductive Properties

Segments of outer medullary collecting duct were dissected from the inner stripe of the rabbit kidney (OMCDi) and perfused in vitro. The conductive properties of the tubule epithelium and individual cell membranes were determined by means of cable analysis and intracellular voltage-recording microelectrodes. In 35 tubules the transepithelial voltage (VT) and resistance (RT) averaged 17.2 +/- 1.4 mV, lumen positive, and 58.6 +/- 5.3 k omega X cm, respectively. The basolateral membrane voltage, (Vbl) was -29.2 +/- 2.1 mV (n = 23). The apical cell membrane did not contain appreciable ion conductances, as evidenced by the high values of apical cell membrane fractional resistance (fRa = Ra/Ra + Rb), which approached unity (0.99 +/- 0.01; n = 23). Moreover, addition of amiloride or BaCl2 to the tubule lumen was without effect on the electrical characteristics of the cell, as was a twofold reduction in luminal [Cl-]. The conductive properties of the basolateral cell membrane were assessed with bath ion substitutions. A twofold reduction in bath [Cl-] depolarized Vbl by 14.7 +/- 0.4 mV (theoretical, 17 mV), while a 10-fold increase in bath [K+] resulted in only a 0.9 +/- 0.4 mV depolarization (theoretical, 61 mV). Substituting bath Na+ with tetramethylammonium (from 150 to 75 mM) was without effect. Reducing bath [HCO-3] from 25 to 5 mM (constant PCO2) resulted in a steady-state depolarization of Vbl of 8.4 +/- 0.4 mV that could not be attributed to conductive HCO-3 movement. Thus, the basolateral cell membrane is predominantly Cl- selective.(ABSTRACT TRUNCATED AT 250 WORDS)

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