Effects of flow rate and potassium intake on distal tubular potassium transfer

1975 ◽  
Vol 228 (4) ◽  
pp. 1249-1261 ◽  
Author(s):  
RN Khuri ◽  
WN Strieder ◽  
G Giebisch
Keyword(s):  
Flow Rate ◽  
Electrical Potential ◽  
Isotonic Saline ◽  
Distal Tubule ◽  
Sodium Reabsorption ◽  
Electrical Potential Difference ◽  
High Potassium ◽  
Flow Rates ◽  
Potassium Intake ◽  
Potassium Secretion

Potassium transport was studied across proximal and distal tubular epithelium in rats on a normal, low- and high-potassium intake during progressive loading with isotonic saline (150 mM) or a moderately hypersomotic urea (200 mM) sodium chloride (100 mM) solution. Free-flow micropuncture and recollection techniques were used during the development of diruesis and tubular fluid (TF) analyzed for inulin-14C, potassium (K) and sodium (Na). Tubular puncture sites were localized by neoprene filling and microdissection. During the large increase in tubular flow rates (10 times): 1) fractional potassium reabsorption fell along the proximal tubule, 2) TFk along the distal tubule remained constant and independent of flow rate in control and high-k rats; thus, net potassium secretion increased in proportion to and was limited by flow rate. 3) In low-K rats TF k fell; with increasing flow rates distal K secretion was not effectively stimulated. 4) Distal tubular sodium reabsorption increased in all animals with flow rate, but tubular Na-K exchange ratios varied greatly. It is suggested that whenever sodium delivery stimulates distal tubular potassium secretion it does so by 1) increasing volume distal tubular potasssium secretion and by 2) augmenting the transepithelial electrical potential difference (lumen negative).

Potassium transport in the distal tubule and collecting duct of the rat

1975 ◽  
Vol 229 (5) ◽  
pp. 1403-1409 ◽  
Author(s):  
HJ Reineck ◽  
RW Osgood ◽  
TF Ferris ◽  
JH Stein
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Distal Tubule ◽  
Potassium Transport ◽  
Distal Convoluted Tubule ◽  
Potassium Excretion ◽  
Flow Rates ◽  
Urinary Potassium ◽  
Potassium Secretion ◽  
Tubular Flow

Because of recent conflicting results, micropuncture studies were performed to clarify the respective role of the distal convoluted tubule and collecting duct in the regulation of urinary potassium excretion. Five groups of Sprague-Dawley rats were studied: group I, hydropenia (n = 10); group II, Ringer loading (n = 7); group III, acute KC1 loading (n = 6); group IV, mannitol diuresis (n = 6); group V, KC1 infusion during mannitol diuresis (n = 7). Early and late distal tubules were identified with intravenous injections of lissamine green. In each animal net secretion of potassium occurred along the distal convoluted tubule, and a direct relationship between distal tubular flow rate and potassium secretion was observed. The magnitude of potassium secretion at high distal tubular flow rates was dependent on the model studied. Potassium transport beyond the distal tubule was evaluated by comparing end distal potassium delivery and fractional potassium excretion. At low urinary flow rates net reabsorption was observed, whereas at higher flow rates no net transport occurred. Thus, flow rate along the collecting duct may be a major determinant of urinary potassium excretion.

Effects of changes in electrical potential difference on tubular potassium transport

1980 ◽  
Vol 238 (3) ◽  
pp. F235-F246 ◽  
Author(s):  
E. Garcia-Filho ◽  
G. Malnic ◽  
G. Giebisch
Keyword(s):  
Potassium Concentration ◽  
Electrical Potential ◽  
Potential Drop ◽  
Plasma Potassium ◽  
Potential Difference ◽  
Electrical Potential Difference ◽  
High Potassium ◽  
Transepithelial Potential ◽  
Wide Range ◽  
Potassium Secretion

To assess directly the role of the transepithelial potential difference (PD) on potassium concentration differences across distal tubular epithelium, continuous and stationary microperfusion experiments were done in tubules voltage-clamped over a wide range of lumen-negative potentials. Potassium was measured either chemically or in situ by potassium-sensitive microelectrodes. Distal cell PD measurements show that most of the potential drop induced by luminal current injection occurred across the luminal cell membrane. Experiments were done in rats either on a control or on a high potassium diet and after amiloride administration. Luminal potassium was highly sensitive to imposed electrical potential changes, attainment of a new steady-state intraluminal potassium concentration was rapid (less than 1 s), and higher luminal potassium concentrations were observed in animals in which potassium secretion had been stimulated. Similar slopes of tubular fluid-to-plasma potassium ratios versus transepithelial potential differences were observed in all experiments. All slopes intersected, at zero PD, at a luminal tubular fluid-to-plasma concentration ratio in excess of unity, indicating the presence of an active component of potassium secretion.

scholarly journals Salivary Electrolyte Concentrations and Electrical Potential Difference Across the Parotid Salivary Duct of Anaesthetized Sodium-Replete Sheep

1980 ◽  
Vol 33 (2) ◽  
pp. 197
Author(s):  
AM Beal
Keyword(s):  
Flow Rate ◽  
Electrical Potential ◽  
Chloride Concentration ◽  
Salivary Flow ◽  
Potential Difference ◽  
Electrical Potential Difference ◽  
Parotid Saliva ◽  
Potential Measurement ◽  
Flow Rates ◽  
Parotid Duct

Salivary flow rate and the concentrations of electrolytes in parotid saliva and arterial plasma from anaesthetized sodium-replete sheep were measured before, during and after ipsilateral intracarotid infusion of acetylcholine at 10 nmol min -1 to ascertain whether anaesthesia altered the relation between salivary flow and sodium concentration. The potential difference (PO) between the lumen of the parotid duct and the vascular system was also measured. Concentrations of salivary sodium and phosphate were decreased and potassium concentration and total CO2 content were increased when rate of salivary flow was increased by acetylcholine infusion. Salivary chloride concentration was reduced in five experiments and increased in three experiments when flow rate was elevated. Thus the flow-composition relations of parotid saliva from anaesthetized sheep were essentially the same as those for saliva from conscious animals. The PO between the lumen of the parotid duct and blood at resting flow rates was 9�4� 1�07 mY, lumen negative. At high flow rates, stimulated by acetylcholine infusion, the PO increased to 21� 9 � 2� 20 mY, lumen negative. This increase in PO of the duct epithelium appeared to depend on changes in the composition of saliva arriving at the site of potential measurement.

Flow-dependent potassium secretion by rabbit cortical collecting tubule in vitro

1987 ◽  
Vol 253 (5) ◽  
pp. F896-F903 ◽  
Author(s):  
B. G. Engbretson ◽  
L. C. Stoner
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Low Flow ◽  
Sodium Reabsorption ◽  
Flow Rates ◽  
Chemical Gradients ◽  
Special Diet ◽  
Potassium Secretion ◽  
Collecting Tubules

Cortical collecting tubules (CCT) dissected from rabbits fed a diet designed to stimulate potassium transport secreted potassium in direct proportion to the flow rate in the range of 0.4-3 nl/min (r = 0.79). This relationship was also evident in tubules from rabbits maintained on standard laboratory chow (r = 0.80). The slope of the line relating the two parameters was almost six times greater in tubules from animals fed the special diet. When the range of flow rates was expanded, potassium secretion in nine CCTs appeared to peak at 5-6 nl/min and then failed to increase despite further elevation of flow to nearly 15 nl/min. We investigated the effects of the electrical and chemical gradients on flow-dependent potassium secretion. Because transepithelial voltage was unaffected by changes in axial flow, we conclude that the flow-dependent fraction of potassium secretion is not explained by the electrical gradient. To evaluate the role of luminal potassium concentration on flow-dependent potassium secretion, 11 CCTs were perfused with both 5 and 50 mM potassium solutions at two flow rates (approximately 1.5 and 4.0 nl/min). Increases in both potassium secretion (15.6 +/- 3.9 peq.mm-1.min-1) and sodium reabsorption (11.9 +/- 5.2 peq.mm-1.min-1) were evident in the tubules perfused with 5 mM potassium. Potassium secretion was not reduced by 50 mM luminal potassium at the low flow rate when the largest chemical gradients opposing net secretion were generated. When 50 mM potassium was present in the lumen, increasing flow did not stimulate potassium secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Hypokalemia Associated with Colonic Pseudo-Obstruction (Ogilvie's Syndrome)

2015 ◽  
Vol 5 (2) ◽  
pp. 118-123 ◽  
Author(s):  
Naseem Sunnoqrot ◽  
Robert F. Reilly
Keyword(s):  
Collecting Duct ◽  
Distal Colon ◽  
Secretory Diarrhea ◽  
Watery Diarrhea ◽  
Pharmacologic Therapy ◽  
Sodium Reabsorption ◽  
Ogilvie's Syndrome ◽  
High Potassium ◽  
Ogilvie’S Syndrome ◽  
Potassium Secretion

We report a case of hypokalemia resulting from colonic pseudo-obstruction or Ogilvie's syndrome. Colonic pseudo-obstruction is characterized by profuse watery diarrhea that has a low sodium and high potassium concentration. It is seen in a variety of medical and surgical conditions, but its exact cause remains unknown. It is thought to result from an imbalance of sympathetic and parasympathetic input in the distal colon. The diarrhea is secretory and driven by potassium secretion rather than the inhibition of sodium reabsorption or chloride secretion, which are the most common pathophysiologic mechanisms of secretory diarrhea. Affected patients often lose >100 mmol of potassium daily. Colonic pseudo-obstruction is associated with a dramatic upregulation of the maxiK or BK potassium channel. This channel plays a prominent role in flow-mediated potassium secretion in the connecting tubule and collecting duct and is also upregulated in the distal colon in patients with advanced chronic kidney disease and end-stage renal disease. In vitro studies show that the channel is regulated by catecholamine binding to the β receptor and cyclic AMP upregulation, somatostatin and aldosterone, insights that can be used to help guide pharmacologic therapy. Nephrologists should be aware of colonic pseudo-obstruction as a cause of extrarenal potassium loss.

Luminal influences on potassium secretion: sodium concentration and fluid flow rate

1979 ◽  
Vol 236 (2) ◽  
pp. F192-F205 ◽  
Author(s):  
D. W. Good ◽  
F. S. Wright
Keyword(s):  
Fluid Flow ◽  
Flow Rate ◽  
Distal Tubule ◽  
Sodium Concentration ◽  
Fluid Flow Rate ◽  
Physiological Range ◽  
Luminal Flow ◽  
Potassium Secretion ◽  
K Concentration

Two methods of in vivo continuous microperfusion were used to evaluate separately luminal sodium concentration and fluid flow rate as factors regulating potassium secretion by the renal distal tubule of the rat. Emphasis was placed on evaluating changes in sodium concentration (43-97 mM) and flow rate (4-27 nl/min) within the physiological range. Absolute rates of Na, K, Cl, and H2O transport were measured. Results showed that increasing early distal flow rate without increasing early distal Na concentration significantly increased the absolute rate of potassium secretion by the distal tubule. In contrast, increasing early distal Na concentration, distal Na delivery, and distal Na absorption did not affect potassium secretion if flow rate was not changed. Further studies showed that reducing early distal Na concentration below the physiological range (to 15 mM) caused the direction of net sodium transport to be reversed but did not significantly reduce potassium secretion. Increasing early distal K concentration (to 34 mM) caused the direction of net potassium transport to be reversed. The rate of potassium secretion appears to depend in part on the luminal potassium concentration. Increases in luminal flow rate may increase the rate of potassium secretion by lowering the luminal K concentration.

Fluorescence imaging study of organic anion transport from renal proximal tubule cell to lumen

1996 ◽  
Vol 271 (3) ◽  
pp. F508-F520 ◽  
Author(s):  
D. S. Miller ◽  
S. Letcher ◽  
D. M. Barnes
Keyword(s):  
Steady State ◽  
Organic Anion ◽  
Electrical Potential ◽  
Imaging Study ◽  
Anion Transport ◽  
Electrical Potential Difference ◽  
Proximal Tubule Cell ◽  
Organic Anion Transport ◽  
Uptake Mechanism ◽  
High Potassium

The mechanisms driving organic anion transport from cell to lumen were studied in intact killifish proximal tubules using fluorescence microscopy. Three fluorescent substrates were used as follows: 1) fluorescein (FL); 2) carboxyfluorescein (CF), generated intracellularly from carboxyfluorescein diacetate (CFDA); and 3) bimane-S conjugates, generated intracellularly by conjugation of monochlorobimane (MCB) with glutathione (GSH) and subsequent metabolism. The latter two substrates bypassed the basolateral uptake mechanism, allowing direct study of luminal transport mechanisms. At steady state, for all three substrates, luminal fluorescence was two to three times higher than cellular fluorescence. With FL as substrate, addition of p-aminohippurate (PAH) or probenecid to the incubation medium reduced cellular and luminal fluorescence to roughly the same extent. With CFDA or MCB as substrate, PAH and probenecid only slightly reduced cellular fluorescence but greatly reduced luminal fluorescence. MCB blocked transport of FL from cell to lumen; CFDA blocked transport of bimane-S conjugates from cell to lumen. Finally, depolarizing tubule cells with high-potassium medium did not affect the steady-state lumen-to-cell distribution of FL, CF, or bimane-S conjugates. These results show that organic anion transport from cell to lumen is mediated and uphill but not sensitive to the electrical potential difference across the luminal membrane.

Potassium transport by the renal distal tubule: effects of potassium loading

1982 ◽  
Vol 243 (5) ◽  
pp. F487-F493 ◽  
Author(s):  
B. A. Stanton ◽  
G. H. Giebisch
Keyword(s):  
Control Diet ◽  
Distal Tubule ◽  
Plasma Potassium ◽  
High Potassium ◽  
Constant Flow Rate ◽  
Potassium Adaptation ◽  
Proximal Tubular ◽  
Potassium Secretion ◽  
Potassium Loading ◽  
The Relationship

Microperfusion studies were performed on superficial distal tubules to determine the relationship between potassium secretion by the distal tubule and plasma potassium concentrations in rats on a control and a high potassium diet. Potassium was infused in graded doses into animals on a control diet and into animals receiving a high potassium diet. Since potassium loading in rats is known to inhibit proximal tubular sodium and fluid reabsorption and thereby could lead to nonspecific flow-related stimulation of potassium secretion by the distal tubule, continuous microperfusion techniques at constant flow rate were used to measure the rate of potassium secretion. Additionally, plasma aldosterone levels were measured and renal clearance experiments carried out. The results show that potassium secretion, restricted to cells of the late distal tubule, reaches a maximal rate at a plasma potassium concentration of about 6 meq/liter. Potassium adaptation significantly enhances potassium secretion compared with animals on a control diet over a range of plasma potassium from 3.8 to 7.4 meq/liter. Enhanced potassium secretion by the distal tubule, in both control and potassium-adapted animals, is associated with increased aldosterone levels.

Postnatal maturation of potassium transport in rabbit cortical collecting duct

1994 ◽  
Vol 266 (1) ◽  
pp. F57-F65 ◽  
Author(s):  
L. M. Satlin
Keyword(s):  
Flow Rate ◽  
Collecting Duct ◽  
Cortical Collecting Duct ◽  
Flow Rates ◽  
Postnatal Maturation ◽  
Significant Linear Correlation ◽  
Potassium Secretion ◽  
Tubular Flow ◽  
Neonatal Kidney

Clearance studies in newborns demonstrate low rates of urinary excretion of potassium, suggesting that the neonatal kidney contributes to the conservation of potassium necessary for growth. Because the cortical collecting duct (CCD) is a primary site for potassium secretion in the adult, we sought to examine the transport capacity of this segment for potassium during postnatal maturation. CCDs isolated from rabbits of various ages (5-6 animals/age group) were microperfused in vitro with solutions simulating plasma. The concentrations of potassium in samples of collected fluid, measured by helium glow photometry, were used to calculate net transport. At a flow rate of approximately 1.6 nl.min-1 x mm-1 net potassium secretion was absent at birth, first became evident at 4 wk of age (-11.08 +/- 2.39 pmol.min-1 x mm-1), and increased sharply thereafter to reach mature rates (-23.08 +/- 3.47 pmol.min-1 x mm-1; P < 0.05) by 6 wk of age. To determine whether low distal tubular flow rates limit net potassium secretion in the neonate, we perfused CCDs at two or more flow rates in the 0.5–5 nl.min-1 x mm-1 range. In CCDs taken from animals > or = 6 wk of age, potassium secretion showed a significant linear correlation with flow rate (y = -10.0x - 7.45; r = 0.87; n = 12).(ABSTRACT TRUNCATED AT 250 WORDS)

Active chloride transport during intestinal secretion

1961 ◽  
Vol 200 (2) ◽  
pp. 309-312 ◽  
Author(s):  
C. S. Tidball
Keyword(s):  
Chloride Transport ◽  
Electrical Potential ◽  
Isotonic Saline ◽  
Extracellular Fluid ◽  
Chloride Concentration ◽  
Potential Gradient ◽  
Intestinal Secretion ◽  
Jejunal Loop ◽  
Electrical Potential Difference ◽  
Calculated Concentration

Characteristically water and chloride ion are absorbed from isotonic saline solutions placed in the in situ jejunal loop of the anesthetized dog. The direction of the water and chloride movement can be reversed by the administration of a cholinergic drug or by the addition of substituted phenols to the isotonic solution bathing the mucosal surface. During such secretion the movement of chloride occurs against a concentration gradient. The transmural electrical potential difference indicates that the lumen is negative with respect to the serosal surface during secretion; thus chloride is also moving against an electrical potential gradient. The calculated concentration of chloride in the fluid moving through the membrane during secretion is higher than the chloride concentration in extracellular fluid which indicates that solvent drag is not responsible for the chloride movement. Therefore active transport of chloride occurs during intestinal secretion.

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