K activity of CCD principal cells from normal and DOCA-treated rabbits

1989 ◽  
Vol 256 (1) ◽  
pp. F136-F142 ◽  
Author(s):  
S. C. Sansom ◽  
S. Agulian ◽  
S. Muto ◽  
V. Illig ◽  
G. Giebisch
Keyword(s):  
Driving Forces ◽  
Basolateral Membrane ◽  
Cell Secretion ◽  
Principal Cells ◽  
K Secretion ◽  
Intracellular K Activity ◽  
K Transport ◽  
Liquid Ion Exchanger ◽  
Electrochemical Equilibrium ◽  
K Activity

We used liquid ion exchanger and conventional microelectrodes to evaluate the effects of mineralocorticoids on the intracellular K activity (aiK) and K transport properties of principal cells (PC) of isolated cortical collecting ducts (CCDs). Hoffman modulation optics and electrophysiological methods were used to identify PC. K activity was measured with two single-barreled electrodes. We found that aiK of PC from deoxycorticosterone acetate (DOCA)-treated rabbits (97.6 mM) was not different from controls (94.8 mM). The driving forces for K transport across the basolateral membrane favored cell to bath (reabsorption) in PCs from controls and bath to cell (secretion) in PCs from DOCA-treated rabbits. However, the driving force for K secretion across the apical membrane was not significantly different between the two groups. We used the intracellular aiKs and bath ion substitutions (gluconate for Cl and K for Na) to evaluate the effects of DOCA on the ion-selective properties of the basolateral membrane of PC. DOCA increased PK/PCl from 0.33 to 0.89. Our conclusion was as follows: in PC of control rabbits K is above electrochemical equilibrium across the basolateral membrane. However, the basolateral K conductance is probably too small for significant K recycling. In PC of DOCA-treated rabbits the aiK is below electrochemical equilibrium across the basolateral membrane and the K conductance is increased. These effects enhance K secretion across this border while maintaining cell K constant.

Characteristics of basolateral Cl- transport by gastric surface epithelium in Necturus antral mucosa

1993 ◽  
Vol 264 (5) ◽  
pp. G910-G920 ◽  
Author(s):  
D. I. Soybel ◽  
M. B. Davis ◽  
L. Y. Cheung
Keyword(s):  
Nutrient Solution ◽  
Cell Membranes ◽  
Basolateral Membrane ◽  
Membrane Potentials ◽  
Gastric Antrum ◽  
Ion Exchanger ◽  
Surface Epithelium ◽  
Antral Mucosa ◽  
Liquid Ion Exchanger ◽  
Electrochemical Equilibrium

Conventional and ion-selective microelectrodes were used to characterize transport of Cl- across the basolateral cell membranes of gastric surface epithelium in isolated preparations of gastric antrum of Necturus. Conventional, voltage-sensing electrodes were used to evaluate changes in membrane potentials and resistances during removal of Cl- from the nutrient perfusate. Liquid ion exchanger Cl(-)-selective microelectrodes were constructed and validated to measure intracellular Cl- activity (aiCl). Our data indicate that 1) aiCl (range 12-25 mM) is close to that predicted if Cl- is distributed across the cell membranes by electrochemical equilibrium, 2) aiCl is not influenced by changes in luminal Cl- content but is susceptible to changes in nutrient Cl- content, 3) Cl- conductances cannot be detected in the basolateral membrane and changes in membrane potentials do not influence aiCl, and 4) Cl- accumulation across the basolateral membrane depends on Na+ and the level of [K+] in the nutrient solution. Inhibition of K(+)-dependent Cl- accumulation, in the absence of nutrient Na+ or in the presence of the inhibitor bumetanide, was demonstrated. These findings suggest that basolateral Na(+)-K(+)-Cl- cotransport is important in regulating cell Cl- levels in surface cells of the gastric antrum in Necturus.

Microelectrode measurements of K+ and pH in rabbit gastric glands: effect of histamine

1984 ◽  
Vol 246 (4) ◽  
pp. G433-G444
Author(s):  
K. Kafoglis ◽  
S. J. Hersey ◽  
J. F. White
Keyword(s):  
Membrane Potential ◽  
Ion Exchange ◽  
Basolateral Membrane ◽  
Free Medium ◽  
Na Transport ◽  
K Uptake ◽  
Gastric Glands ◽  
Microelectrode Measurements ◽  
Intracellular K Activity ◽  
K Activity

Conventional and liquid ion-exchange microelectrodes sensitive to K+ or pH were used to examine the response of isolated rabbit gastric glands to histamine. The epithelial cells were impaled across the basolateral membrane. The membrane potential averaged -6.1 +/- 0.6 mV and was unchanged after replacement of medium K+, Cl-, or Na+. The intracellular K+ activity (alpha iK) averaged 41.3 +/- 3.0 mM, indicating K+ accumulation by a factor of 6.8. Active accumulation of K+ was eliminated by ouabain. In contrast, histamine increased K+ activity to 55.3 +/- 3.9 mM. This stimulation was blocked by ouabain. In glands bathed in a Na+-free medium containing ouabain, addition of histamine elevated alpha iK from 12.5 +/- 0.7 to 17.1 +/- 1.1 mM. Isobutylmethylxanthine (10(-4) M) also elevated alpha iK. When impaled with pH-sensitive microelectrodes, glands exposed to histamine exhibited regions of acidity as low as pH 3. Acidification was also produced by histamine after medium Na+ had been replaced with choline. Picoprazole (H 149/94) blocked the effects of histamine on alpha iK and gland pH. The results are consistent with the view that histamine-induced acid secretion by gastric glands is associated with K+ uptake by a mechanism that is independent of Na+ transport but is inhibited by intracellular Na+. This is most likely the H+-K+-ATPase on the secretory surface of the gland cells. Evidence that some tissue K+ is bound or compartmentalized is also discussed.

Potassium transport by flounder intestinal mucosa

1984 ◽  
Vol 246 (6) ◽  
pp. F946-F951 ◽  
Author(s):  
R. A. Frizzell ◽  
D. R. Halm ◽  
M. W. Musch ◽  
C. P. Stewart ◽  
M. Field
Keyword(s):  
Apical Membrane ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Electrical Potential Difference ◽  
Cell Type ◽  
K Secretion ◽  
Single Cell Type ◽  
Free Media ◽  
Membrane Electrical Potential ◽  
K Transport

We studied the mechanisms of K transport across an epithelium in which NaCl absorption is mediated primarily by Na/K/Cl cotransport at the apical membrane. Rubidium served as a reliable K substitute; under control conditions, both K and Rb were actively secreted. During secretion, K (Rb) enters across the basolateral membrane via the Na/K pump and exits across the apical membrane through K conductance pathways, since serosal ouabain or mucosal barium abolished K secretion, mucosal furosemide or Cl-free media blocked K secretion by interfering with access of Na to the pump, and elevated mucosal solution [K] or [Rb] depolarized the apical membrane electrical potential difference. Mucosal Ba unmasked active Rb absorption that could be blocked by mucosal furosemide. These findings illustrate active K absorption and secretion across an epithelium that comprises a single cell type in which opposing K fluxes across the apical membrane are mediated by Na/K/Cl cotransport entry and conductive K exit. The direction of transepithelial K transport is determined by the relative activities of these pathways.

scholarly journals The effect of extracellular potassium on the intracellular potassium ion activity and transmembrane potentials of beating canine cardiac Purkinje fibers.

1977 ◽  
Vol 69 (4) ◽  
pp. 463-474 ◽  
Author(s):  
D S Miura ◽  
B F Hoffman ◽  
M R Rosen
Keyword(s):  
Equilibrium Potential ◽  
Extracellular Potassium ◽  
Purkinje Fibers ◽  
Transmembrane Potentials ◽  
Cardiac Purkinje Fibers ◽  
K Concentration ◽  
Range Of Values ◽  
Intracellular K Activity ◽  
Liquid Ion Exchanger ◽  
K Activity

We used open tip microelectrodes containing a K+-sensitive liquid ion exchanger to determine directly the intracellular K+ activity in beating canine cardiac Purkinje fibers. For preparations superfused with Tyrode's solution in which the K+ concentration was 4.0 mM, intracellular K+ activity (ak) was 130.0+/-2.3 mM (mean+/-SE) at 37 degrees C. The calculated K+ equilibrium potential (EK) was -100.6+/-0.5 mV. Maximum diastolic potential (ED) and resting transmembrane potential (EM) were measured with conventional microelectrodes filled with 3 M KCl and were -90.6+/-0.3 and -84.4+/-0.4 mV, respectively. When [K+]o was decreased to 2.0 mM or increased to 6.0, 10.0, and 16.0 mM, ak remained the same. At [K+]o=2.0, ED was -97.3+/-0.4 and Em -86.0+/-0.7 mV; at [K+]o=16.0, ED fell to -53.8+/-0.4 mV and Em to the same value. Over this range of values for [K+]o, EK changed from -119.0+/-0.3 to -63.6+/-0.2 mV. These values for EK are consistent with those previously estimated indirectly by other techniques.

scholarly journals Intracellular K+ activity and its relation to basolateral membrane ion transport in Necturus gallbladder epithelium.

1980 ◽  
Vol 76 (1) ◽  
pp. 33-52 ◽  
Author(s):  
L Reuss ◽  
S A Weinman ◽  
T P Grady
Keyword(s):  
Cell Membrane ◽  
Amphotericin B ◽  
Basolateral Membrane ◽  
Membrane Potentials ◽  
Equilibrium Potential ◽  
Gallbladder Epithelium ◽  
Bathing Medium ◽  
Necturus Gallbladder ◽  
Intracellular K Activity ◽  
K Activity

A study of the mechanisms of the effects of amphotericin B and ouabain on cell membrane and transepithelial potentials and intracellular K activity (alpha Ki) of Necturus gallbladder epithelium was undertaken with conventional and K-selective intracellular microelectrode techniques. Amphotericin B produced a mucosa-negative change of transepithelial potential (Vms) and depolarization of both apical and basolateral membranes. Rapid fall of alpha Ki was also observed, with the consequent reduction of the K equilibrium potential (EK) across both the apical and the basolateral membrane. It was also shown that, unless the mucosal bathing medium is rapidly exchanged, K accumulates in the unstirred fluid layers near the luminal membrane generating a paracellular K diffusion potential, which contributes to the Vms change. Exposure to ouabain resulted in a slow decrease of alpha Ki and slow depolarization of both cell membranes. Cell membrane potentials and alpha Ki could be partially restored by a brief (3-4 min) mucosal substitution of K for Na. Under all experimental conditions (control, amphotericin B, and ouabain), EK at the basolateral membrane was larger than the basolateral membrane equivalent emf (Eb). Therefore, the K chemical potential difference appears to account for Eb and the magnitude of the cell membrane potentials, without the need to postulate an electrogenic Na pump. Comparison of the rate of Na transport across the tissue with the electrodiffusional K flux across the basolateral membrane indicates that maintenance of a steady-state alpha Ki cannot be explained by a simple Na,K pump-K leak model. It is suggested that either a NaCl pump operates in parallel with the Na,K pump, or that a KCl downhill neutral extrusion mechanism exists in addition to the electrodiffusional K pathway.

scholarly journals Electrophysiology of flounder intestinal mucosa. I. Conductance properties of the cellular and paracellular pathways.

1985 ◽  
Vol 85 (6) ◽  
pp. 843-864 ◽  
Author(s):  
D R Halm ◽  
E J Krasny ◽  
R A Frizzell
Keyword(s):  
Membrane Potential ◽  
Apical Membrane ◽  
Driving Forces ◽  
Basolateral Membrane ◽  
Electrical Potential ◽  
Membrane Conductance ◽  
Equivalent Circuit Analysis ◽  
K Secretion ◽  
Paracellular Pathways ◽  
K Concentration

We evaluated the conductances for ion flow across the cellular and paracellular pathways of flounder intestine using microelectrode techniques and ion-replacement studies. Apical membrane conductance properties are dominated by the presence of Ba-sensitive K channels. An elevated mucosal solution K concentration, [K]m, depolarized the apical membrane potential (psi a) and, at [K]m less than 40 mM, the K dependence of psi a was abolished by 1-2 mM mucosal Ba. The basolateral membrane displayed Cl conductance behavior, as evidenced by depolarization of the basolateral membrane potential (psi b) with reduced serosal Cl concentrations, [Cl]s. psi b was unaffected by changes in [K]s or [Na]s. From the effect of mucosal Ba on transepithelial K selectivity, we estimated that paracellular conductance (Gp) normally accounts for 96% of transepithelial conductance (Gt). The high Gp attenuates the contribution of the cellular pathway to psi t while permitting the apical K and basolateral Cl conductances to influence the electrical potential differences across both membranes. Thus, psi a and psi b (approximately 60 mV, inside negative) lie between the equilibrium potentials for K (76 mV) and Cl (40 mV), thereby establishing driving forces for K secretion across the apical membrane and Cl absorption across the basolateral membrane. Equivalent circuit analysis suggests that apical conductance (Ga approximately equal to 5 mS/cm2) is sufficient to account for the observed rate of K secretion, but that basolateral conductance (Gb approximately equal to 1.5 mS/cm2) would account for only 50% of net Cl absorption. This, together with our failure to detect a basolateral K conductance, suggests that Cl absorption across this barrier involves KCl co-transport.

Renal potassium transport: morphological and functional adaptations

1989 ◽  
Vol 257 (5) ◽  
pp. R989-R997 ◽  
Author(s):  
B. A. Stanton
Keyword(s):  
Collecting Duct ◽  
Cell Structure ◽  
Basolateral Membrane ◽  
Distal Tubule ◽  
Morphological Evidence ◽  
Intercalated Cells ◽  
Principal Cells ◽  
K Secretion ◽  
K Concentration ◽  
And Function

Maintenance of K+ homeostasis in mammals and amphibians depends primarily on the kidneys which excrete 95% of K+ ingested in the diet. The amount of K+ in the urine is determined by the rate of K+ secretion or absorption by the distal tubule and the collecting duct. When K+ intake is increased, K+ secretion rises. The mechanisms of K+ secretion by the distal tubule and collecting duct are so efficient that K+ intake can increase 20-fold with little or no increase in body K+ content or in plasma K+ concentration. Elevated K+ secretion by the distal tubule and collecting duct occurs in part because of an increase in the quantity of Na+-K+-adenosinetriphosphatase (Na+-K+-ATPase) and amplification of the basolateral membrane of principal cells. When dietary K+ intake is reduced, urinary K+ excretion falls, because K+ secretory mechanisms are suppressed and K+ absorptive mechanisms, residing in the distal tubule and collecting duct, are activated. Because a low-K+ diet is associated with hypertrophy of intercalated cells, it has been suggested that this cell type absorbs K+, possibly by an H+-K+-ATPase. In this review, I discuss the functional and morphological evidence that supports the view that principal cells secrete K+ and that intercalated cells absorb K+. In addition, some of the hormones and factors that are responsible for these changes in cell structure and function are discussed.

scholarly journals Driving forces and pathways for H+ and K+ transport in insect midgut goblet cells.

1992 ◽  
Vol 172 (1) ◽  
pp. 403-415 ◽  
Author(s):  
D F Moffett ◽  
A Koch
Keyword(s):  
Driving Forces ◽  
Goblet Cells ◽  
Bathing Solution ◽  
Entry And Exit ◽  
Insect Midgut ◽  
Lepidopteran Insects ◽  
Lateral Intercellular Spaces ◽  
K Secretion ◽  
K Transport ◽  
Primary Active Transport

In the midgut of larval lepidopteran insects, goblet cells are believed to secrete K+; the proposed mechanism involves an electrogenic K+/nH+ (n > 1) antiporter coupled to primary active transport of H+ by a vacuolar-type ATPase. Goblet cells have a prominent apical cavity isolated from the gut lumen by a valve-like structure. Using H(+)- and K(+)-selective microelectrodes, we showed that electrochemical gradients of H+ and K+ across the apical membrane and valve are consistent with active secretion of both ions into the cavity and that the transapical H+ electrochemical gradient, but not the transapical pH gradient, is competent to drive K+ secretion by a K+/nH+ antiporter. We used 10 mmol l-1 tetramethylammonium ion (TMA+) as a marker for the ability of small cations to pass from the gut lumen through the valve to the goblet cavity, exploiting the high TMA+ sensitivity of 'K(+)-sensitive' microelectrodes. These studies showed that more than half of the cavities were inaccessible to TMA+. For those cavities that were accessible to TMA+, both entry and exit rates were too slow to be consistent with direct entry through the valves. One or more mixing compartments appear to lie between the lumen bathing solution and the goblet cavity. The lateral intercellular spaces and goblet cell cytoplasm are the most likely compartments. The results are not consistent with free diffusion of ions in a macroscopic valve passage; mechanisms that would allow K+ secreted into the goblet cavity to exit to the gut lumen, while preventing H+ from exiting, remain unclear.

Vasopressin and mineralocorticoid increase apical membrane driving force for K+ secretion in rat CCD

1990 ◽  
Vol 258 (1) ◽  
pp. F199-F210 ◽  
Author(s):  
J. A. Schafer ◽  
S. L. Troutman ◽  
E. Schlatter
Keyword(s):  
Driving Force ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Membrane Voltage ◽  
Bathing Solution ◽  
Sprague Dawley ◽  
Principal Cells ◽  
Sprague Dawley Rats ◽  
K Secretion

Cortical collecting ducts (CCD) from untreated Sprague-Dawley rats were perfused and bathed in vitro with modified Krebs-Ringer solutions. Arginine vasopressin (AVP;100 microU/ml) in the bathing solution hyperpolarized the transepithelial voltage (PDT, mV) from -2.3 +/- 0.7 (control) to -6.0 +/- 1.1 (n = 22) and decreased the transepithelial resistance from 64 +/- 7 to 54 +/- 7 omega.cm2 (n = 21). AVP depolarized the basolateral membrane voltage of principal cells (PDbl) only slightly (but significantly by paired statistical comparison) from -85 +/- 1 to -84 +/- 1 mV (n = 9), with a fall in the fractional resistance of the apical membrane (FRa) from 0.82 +/- 0.03 to 0.77 +/- 0.05 (n = 9). Luminal amiloride (10 microM) produced no change in FRa in the absence of AVP, but in the presence of AVP increased FRa to the same level observed in the absence of AVP. The changes with AVP were significantly less than those observed by us previously in deoxycorticosterone (DOC)-treated animals (E. Schlatter and J. A. Schafer. Pfluegers Arch. 409:81-92, 1987), indicating that the observed synergism between DOC and AVP in stimulating Na+ absorption is attributable to a greater increase in the Na+ conductance in the apical membrane of principal cells with AVP in the DOC-treated CCD than in the normal. Furthermore, we have calculated that the depolarization of apical membrane voltage resulting from the increased Na+ conductance produced by either or both AVP and DOC increases the driving force for K+ exit across the apical membrane in proportion to the previously measured increase in secretion. This increase in driving force may be sufficient to explain the increased K+ secretion produced by these hormones with no change in the apical membrane K+ conductance.

Analysis of K+ transport by rabbit CCD: conductive pathways and K(+)-K+ exchange by Na(+)-K+ pump

1992 ◽  
Vol 262 (1) ◽  
pp. F86-F97 ◽  
Author(s):  
T. Nonaka ◽  
D. H. Warden ◽  
J. B. Stokes
Keyword(s):  
Apical Membrane ◽  
Collecting Duct ◽  
Basolateral Membrane ◽  
Cortical Collecting Duct ◽  
Na Transport ◽  
Epithelial Na Channels ◽  
Electrophysiological Measurements ◽  
K Secretion ◽  
Cellular Pathways ◽  
K Transport

We studied the cellular pathways of K+ transport by the rabbit cortical collecting duct that was stimulated to absorb Na+ and to secrete K+. The vast majority of K+ secretion (into the lumen) was inhibited by benzamil, a blocker of epithelial Na+ channels. The residual K+ secretion was completely inhibited by ouabain. Thus all active K+ secretion was dependent on Na+ transport by the Na(+)-K+ pump. The passive pathways of K+ transport were further examined using tracer and electrophysiological measurements. K+ transfer across the apical membrane was predominantly or exclusively conductive; the apical K+ conductance was 31 mS/cm2. The basolateral membrane contained two pathways for K+ tracer translocation. The (barium-sensitive) conductive pathway accounted for a relatively small (12-20%) portion of the tracer permeation. A larger pathway appeared to be via K(+)-K+ exchange on the Na(+)-K+ pump. The magnitude of the Ba2(+)-sensitive (basolateral) K+ conductance predicted a substantially larger tracer flux than was actually measured. The best explanation for this difference is the presence of single-file diffusion through K+ channels on the apical and basolateral membranes. An analysis of the electrically silent K+ transport from lumen to bath suggests that the Na(+)-K+ pump can vary the ratio of its Na(+)-K+ and K(+)-K+ modes of operation. When the tubule is actively transporting Na+ and K+, the Na(+)-K+/K(+)-K+ turnover ratio is greater than 7. When Na+ transport is limited by inhibiting Na+ entry across the apical membrane, the ratio falls to less than 1. A major factor determining this ratio is probably the availability of Na+ to the cytoplasmic side of the pump.

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