Is the voltage divider ratio a reliable estimate of the resistance ratio of the cell membranes in tubular epithelia?

1985 ◽  
Vol 403 (4) ◽  
pp. 388-395 ◽  
Author(s):  
D. I. Cook ◽  
E. Fr�mter
Keyword(s):  
Cell Membranes ◽  
Voltage Divider ◽  
Resistance Ratio ◽  
Reliable Estimate ◽  
Voltage Divider Ratio

Contribution of surface epithelial cells to total conductance of Necturus gastric fundus mucosa

1996 ◽  
Vol 270 (6) ◽  
pp. G902-G908 ◽  
Author(s):  
G. Kottra ◽  
C. Iacovelli ◽  
R. Caroppo ◽  
S. Curci ◽  
P. Bakos ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Voltage Divider ◽  
Gastric Fundus ◽  
Total Conductance ◽  
In Vitro Activation ◽  
Transepithelial Voltage ◽  
Gastric Fundus Mucosa ◽  
Voltage Divider Ratio ◽  
Microelectrode Techniques

Microelectrode techniques were used to quantify the contribution of surface epithelial cells (SEC) to transepithelial conductance (gt) of Necturus gastric fundus mucosa. Transepithelial voltage (Vt) and resistance (Rt) as well as the basolateral cell membrane potential (Vb) and voltage divider ratio of SEC were measured. Freshly mounted preparations did not respond to luminal amiloride (10 microM), but within 2-3 h a significant response developed (delta Vt = 3.8 +/- 1.2 mV, delta Rt = 63 +/- 23 omega cm2, and delta Vb = -6.9 +/- 1.3 mV), indicating activation of an apical Na+ conductance in SEC. Using circuit analysis equations, we calculate that SEC contribute 10.4% to gt under control conditions and 13.0% after Na+ conductance activation. Histamine (0.1 mM), which stimulates the oxyntopeptic cells (OC), increased Vt and decreased Rt but did not significantly alter the membrane resistances of SEC. As a result, the contribution of SEC to gt fell to 7.4 or 9.3%, respectively. The data confirm that SEC are poorly permeable and that the major conductance path across gastric mucosa leads through OC in the glands. The reason for the protracted in vitro activation of the apical Na+ conductance in SEC is not known.

Localization of Cl- conductance in normal and Cl- impermeability in cystic fibrosis sweat duct epithelium

1989 ◽  
Vol 257 (4) ◽  
pp. C727-C735 ◽  
Author(s):  
M. M. Reddy ◽  
P. M. Quinton
Keyword(s):  
Cystic Fibrosis ◽  
Basolateral Membrane ◽  
Voltage Divider ◽  
Sweat Duct ◽  
Basolateral Membranes ◽  
Duct Epithelium ◽  
Voltage Divider Ratio ◽  
Normal Duct ◽  
Cl Conductance ◽  
Cl Permeability

We studied the Cl- permeability properties of apical and basolateral membranes of human reabsorptive sweat duct (RSD) from normal and cystic fibrosis (CF) subjects. In normal ducts, Cl- substitution by impermeant anion gluconate in the lumen increased the voltage divider ratio (VDR) from 4.8 +/- 0.9 to 7.0 +/- 1.1 (n = 8, P less than 0.05), whereas Cl- substitution in the contraluminal bath decreased the VDR from 3.2 +/- 0.7 to 1.9 +/- 0.4 (n = 7, P less than 0.05). These results are consistent with a significant Cl- permeability in both apical and basolateral membranes of normal ducts. Amiloride (10(-4) M) in the lumen of normal ducts resulted in a small increase in VDR from 4.2 +/- 0.6 to 5.0 +/- 0.8 (n = 10, P less than 0.05), whereas the current-induced basolateral membrane voltage deflections (delta Vb) increased from 6.9 +/- 1.3 to 7.7 +/- 1.2 mV, suggesting that inhibition of Na+ permeability decreased basolateral membrane Cl- permeability. In the absence of luminal Cl-, amiloride decreased delta Vb and induced much greater effect on VDR (from 5.2 +/- 1.1 to 10.8 +/- 2.3, n = 9, P less than 0.05) than in the presence of Cl-. Likewise, in the presence of amiloride, Cl- substitution in the lumen had greater effect on VDR (increased from 3.5 +/- 0.5 0.5 to 10.0 +/- 1.5, n = 15, P less than 0.05) than in the absence of amiloride. These results indicate that Na+ conductance in the apical membrane of the normal duct is significantly smaller than Cl- conductance.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of histamine on the basolateral K+ conductance of frog stomach oxyntic cells and surface epithelial cells

1990 ◽  
Vol 258 (4) ◽  
pp. G631-G636
Author(s):  
L. Debellis ◽  
S. Curci ◽  
E. Fromter
Keyword(s):  
Epithelial Cells ◽  
Basolateral Membrane ◽  
Voltage Divider ◽  
Cell Types ◽  
Membrane Resistance ◽  
Rana Esculenta ◽  
Frog Stomach ◽  
K Concentration ◽  
Voltage Divider Ratio ◽  
Ion Conductances

The transepithelial potential difference (Vt) and resistance (Rt) and the basolateral cell membrane potential (Vs) of oxyntic cells (OC) and surface epithelial cells (SEC) were measured in isolated stomachs of Rana esculenta. At rest, Vs of OC and SEC was virtually identical [-66.3 +/- 4.5 (SD) (n = 10) and -67.3 +/- 5.9 mV (n = 9)] and both cells responded to increasing serosal K+ concentration from 4 to 13 mmol/l with virtually the same depolarization (delta Vs,K) of +16.2 +/- 2.0 and +16.0 +/- 2.9 mV, respectively, while Vt declined by approximately half as much. Histamine (0.1 mmol/l) reduced Vt and Rt and increased the voltage divider ratio in both cell types, indicating a fall in basolateral membrane resistance. In the OC, this increase was neither associated with a significant alteration of Vs nor with a change in delta Vs,K. In the SEC, however, histamine markedly increased Vs to -75.5 +/- 7.3 mV (n = 9) as well as delta Vs,K to +18.5 +/- 2.6 mV, which was paralleled by an increase in delta Vt,K from 9.8 +/- 3.9 to +12.8 +/- 4.2 mV. The data indicate that 1) both OC and SEC respond to histamine, 2) both OC and SEC contain a basolateral K+ conductance that increases under histamine (in OC probably, in parallel with other ion conductances), and 3) in Rana esculenta the SEC contribute substantially to Vt.

Ca-sensitive Na transport in sheep omasum

1999 ◽  
Vol 276 (6) ◽  
pp. G1331-G1344 ◽  
Author(s):  
Gerhard Schultheiss ◽  
Holger Martens
Keyword(s):  
Divalent Cations ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Voltage Divider ◽  
Close Correlation ◽  
Na Transport ◽  
Luminal Side ◽  
Flux Measurements ◽  
Voltage Divider Ratio ◽  
Peak Value

Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current ( I sc), with a range of 1–4 μeq ⋅ h−1 ⋅ cm−2. A Michaelis-Menten-type kinetic was found between the Na concentration and the I sc(Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 μeq ⋅ h−1 ⋅ cm−2). Mucosal amiloride (1 mM), phenamil (1 or 10 μ), or serosal aldosterone (1 μM for 6 h) did not change I sc. Removal of divalent cations (Ca and Mg) enhanced I sc considerably from 2.61 ± 0.24 to a peak value of 11.18 ± 1.1 μeq ⋅ h−1 ⋅ cm−2. The peak I sc(overshoot) immediately declined to a plateau I sc of ∼6–7 μeq ⋅ h−1 ⋅ cm−2. Na flux measurements showed a close correlation between changes in I sc and Na transport. Transepithelial studies demonstrated that K, Cs, Rb, and Li are transported, indicating putative nonselective cation channels, which are inhibited by divalent cations (including Ca, Mg, Sr, Ba) and by (trivalent) La. Intracellular microelectrode recordings from the luminal side clearly showed changes of voltage divider ratio when mucosal divalent cations were removed. The obtained data support the assumption of a distinct electrogenic Na transport mechanism in sheep omasum.

scholarly journals Nystatin as a probe for investigating the electrical properties of a tight epithelium.

1977 ◽  
Vol 70 (4) ◽  
pp. 427-440 ◽  
Author(s):  
S A Lewis ◽  
D C Eaton ◽  
C Clausen ◽  
J M Diamond
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Voltage Divider ◽  
Junctional Conductance ◽  
Transepithelial Voltage ◽  
Almost All ◽  
Voltage Divider Ratio ◽  
Rabbit Urinary Bladder ◽  
Tight Epithelium

We show how the antibiotic nystatin may be used in conjunction with microelectrodes to resolve transepithelial conductance Gt into its components: Ga, apical membrane conductance; Gbl, basolateral membrane conductance; and Gj, junctional conductance. Mucosal addition of nystatin to rabbit urinary bladder in Na+-containing solutions caused Gt to increase severalfold to ca. 460 micrometerho/muF, and caused the transepithelial voltage Vt to approach +50 mV regardless of its initial value. From measurements of Gt and the voltage-divider ratio as a function of time after addition or removal of nystatin, values for Ga, Gbl, and Gj of untreated bladder could be obtained. Nystatin proved to have no direct effect on Gbl or Gj but to increase Ga by about two orders of magnitude, so that the basolateral membrane then provided almost all of the electrical resistance in the transcellular pathway. The nystatin channel in the apical membrane was more permeable to cations than to anions. The dose-response curve for nystatin had a slope of 4.6. Use of nystatin permitted assessment of whether microelectrode impalement introduced a significant shunt conductance into the untreated apical membrane, with the conclusion that such a shunt was negligible in the present experiments. Nystatin caused a hyperpolarization of the basolateral membrane potential in Na+-containing solutions. This may indicate that the Na+ pump in this membrane is electrogenic.

Photoreceptor disk membrane substructures by means of the complementary freeze-fracture-replica methods

1978 ◽  
Vol 36 (2) ◽  
pp. 156-157
Author(s):  
A. Tonosaki ◽  
M. Yamasaki ◽  
H. Washioka ◽  
J. Mizoguchi
Keyword(s):  
Cell Membranes ◽  
Freeze Fracture ◽  
Purple Membrane ◽  
Remarkable Case ◽  
Single Face ◽  
Disk Membrane ◽  
Associated Proteins ◽  
Photoreceptor Membranes

A vertebrate disk membrane is composed of 40 % lipids and 60 % proteins. Its fracture faces have been classed into the plasmic (PF) and exoplasmic faces (EF), complementary with each other, like those of most other types of cell membranes. The hypothesis assuming the PF particles as representing membrane-associated proteins has been challenged by serious questions if they in fact emerge from the crystalline formation or decoration effects during freezing and shadowing processes. This problem seems to be yet unanswered, despite the remarkable case of the purple membrane of Halobacterium, partly because most observations have been made on the replicas from a single face of specimen, and partly because, in the case of photoreceptor membranes, the conformation of a rhodopsin and its relatives remains yet uncertain. The former defect seems to be partially fulfilled with complementary replica methods.

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