Luminal chloride, HEINO
influences on potassium secretion: sodium, and thiazide diuretics VELAZQUEZ,
DAVID
H. ELLISON,
AND FRED
S. WRIGHT
Yale University School of Medicine, New Haven 06510; and Department of Veterans Affairs Medical Center, West Haven, Connecticut 06516 VelBzquez, Heino, David H. Ellison, and Fred S. Wright. Luminal influences on potassium secretion: chloride, sodium, and thiazide diuretics. Am. J. Physiol. 262 (Renal Fluid Electrolyte Physiol. 31): F1076-1082, 1992.-In the presence of Cl-, K+ secretion by the distal tubule saturates with increasing luminal Na+ concentration. Apparent maximal K+ secretion is attained with luminal Na+ concentrations of 40 mM. The results of the present study show that lowering the Cl- concentration of luminal fluid can increase the level of Na+-stimulated K+ secretion beyond the maximal level attained in the presence of Cl-. The effect of lowering luminal Cl- concentration to ~10 mM on K+ secretion is greater with higher Na+ concentration. Under these conditions, chlorothiazide decreases K+ secretion. When chlorothiazide is present, changing the Na+ concentration does not affect K+ secretion. Because in rats a thiazide effect is attributed primarily to the distal convoluted tubule (DCT), we postulate that it is primarily DCT cells that increase K+ secretion when Na+ concentration is raised in the presence of low luminal Cl- concentration. We propose that the rat DCT cells have both an absorptive Na+-Clcotransport mechanism and a secretory K+-Clcotransport mechanism in the luminal membrane that can mediate the apparent exchange of Na+ for K+.
luminal Cl- increased K+ secretion in both of these regions. In these experiments luminal Na+ was held constant at either 75 or 150 mM (12). The observations of separate stimulatory effects of either raising luminal Na+ concentration with Cl- held constant or lowering luminal Cl- concentration with Na+ held constant led us to ask whether these regulatory factors might interact. In addition, the stimulation of K+ secretion by reducing luminal Cl- was seen in tubules with luminal Na+ concentration well above the 40 mM value previously seen to stimulate maximally. This consideration raised the possibility that the maximal rate of K+ secretion produced by increasing Na+ concentration depends on the level of Cl- in the lumen. The present experiments were carried out to test the hypothesis that the effect of increasing luminal Na+ concentration to stimulate K+ secretion by the distal tubule is greater when luminal Cl- concentration is low compared with when luminal Cl- is kept high.
rat; kidney; distal convoluted tubule; chlorothiazide; chloride cotransport; potassium-chloride cotransport; port; gluconate
Adult male Sprague-Dawley rats (Harlan Sprague-Dawley, Indianapolis, IN), weighing 180-280 g, were allowed free access to standard (Purina Mills, Lab Animal Division, Gray Summit, MO; 9.6 g NaCl/kg diet) or low-NaCl (ICN Biochemicals, Cleveland, OH; 0.292 g NaCl/kg diet) rat chow (5) and tap water up to the time of the experiment. The rats were anesthetized by intraperitoneal injection of 100-110 mg/kg body wt of 5-secbutyl-5ethyl-2-thiobarbituric acid (Inactin; Byk-Gulden, Constance, FRG) and prepared surgically for micropuncture as described previously (7). Briefly, the rats were placed on a heated table to maintain body temperature at 37°C. A carotid artery was cannulated to measure blood pressure, and two catheters were inserted into a jugular vein, one for infusion (10 ml h-l kg body wt-l) of either a salt solution (140 mM NaCl, 4 mM KCl; microperfusion experiments) or a glucose solution (275 mM; clearance experiments) and the other to administer supplementary Inactin if necessary. A tracheostomy was performed. The left kidney was exposed by a flank incision, placed in a plastic cup, and observed under a stereomicroscope at X160. An additional 2 ml of infusion solution were administered during the surgical preparation. Microperfusion experiments. All distal microperfusion experiments were performed on animals fed standard chow and as described previously (7,15). In brief, distal tubules were selected for study if at least two loops were accessible at the kidney surface. They were located by injecting stained (FD & C Blue no. 1; Kohnstamm, New York, NY) saline into a proximal tubule loop and visualizing the dyed solution in the lumen of the distal tubule of the same nephron. A perfusion pipette was placed in the upstream distal loop. The proximal tubule of that
sodiumtrans-
known to affect the rate of distal tubule1 K+ secretion are the concentrations of Na+ and Cl- in the tubule lumen (2, 3, 6, 7, 12, 15). With the Cl- concentration maintained at 100 mM and the tubule fluid flow rate held constant, the greatest sensitivity to changes in luminal Na+ concentration has been observed in perfused rat distal tubules to be in the range ~40 mM (6, 7). In the range >40 mM, increases in luminal Na+ have little effect on K+ secretion. The apparent Michaelis constant of this relationship is 11 mM (6). Distal K+ secretion also responds to changes in the luminal concentration of Cl- (2, 3, 6, 12, 15). Microperfusion experiments in which the luminal Cl- concentration was reduced to levels
influences on potassium secretion: sodium, and thiazide diuretics VELAZQUEZ,
DAVID
H. ELLISON,
AND FRED
S. WRIGHT
Yale University School of Medicine, New Haven 06510; and Department of Veterans Affairs Medical Center, West Haven, Connecticut 06516 VelBzquez, Heino, David H. Ellison, and Fred S. Wright. Luminal influences on potassium secretion: chloride, sodium, and thiazide diuretics. Am. J. Physiol. 262 (Renal Fluid Electrolyte Physiol. 31): F1076-1082, 1992.-In the presence of Cl-, K+ secretion by the distal tubule saturates with increasing luminal Na+ concentration. Apparent maximal K+ secretion is attained with luminal Na+ concentrations of 40 mM. The results of the present study show that lowering the Cl- concentration of luminal fluid can increase the level of Na+-stimulated K+ secretion beyond the maximal level attained in the presence of Cl-. The effect of lowering luminal Cl- concentration to ~10 mM on K+ secretion is greater with higher Na+ concentration. Under these conditions, chlorothiazide decreases K+ secretion. When chlorothiazide is present, changing the Na+ concentration does not affect K+ secretion. Because in rats a thiazide effect is attributed primarily to the distal convoluted tubule (DCT), we postulate that it is primarily DCT cells that increase K+ secretion when Na+ concentration is raised in the presence of low luminal Cl- concentration. We propose that the rat DCT cells have both an absorptive Na+-Clcotransport mechanism and a secretory K+-Clcotransport mechanism in the luminal membrane that can mediate the apparent exchange of Na+ for K+.
luminal Cl- increased K+ secretion in both of these regions. In these experiments luminal Na+ was held constant at either 75 or 150 mM (12). The observations of separate stimulatory effects of either raising luminal Na+ concentration with Cl- held constant or lowering luminal Cl- concentration with Na+ held constant led us to ask whether these regulatory factors might interact. In addition, the stimulation of K+ secretion by reducing luminal Cl- was seen in tubules with luminal Na+ concentration well above the 40 mM value previously seen to stimulate maximally. This consideration raised the possibility that the maximal rate of K+ secretion produced by increasing Na+ concentration depends on the level of Cl- in the lumen. The present experiments were carried out to test the hypothesis that the effect of increasing luminal Na+ concentration to stimulate K+ secretion by the distal tubule is greater when luminal Cl- concentration is low compared with when luminal Cl- is kept high.
rat; kidney; distal convoluted tubule; chlorothiazide; chloride cotransport; potassium-chloride cotransport; port; gluconate
Adult male Sprague-Dawley rats (Harlan Sprague-Dawley, Indianapolis, IN), weighing 180-280 g, were allowed free access to standard (Purina Mills, Lab Animal Division, Gray Summit, MO; 9.6 g NaCl/kg diet) or low-NaCl (ICN Biochemicals, Cleveland, OH; 0.292 g NaCl/kg diet) rat chow (5) and tap water up to the time of the experiment. The rats were anesthetized by intraperitoneal injection of 100-110 mg/kg body wt of 5-secbutyl-5ethyl-2-thiobarbituric acid (Inactin; Byk-Gulden, Constance, FRG) and prepared surgically for micropuncture as described previously (7). Briefly, the rats were placed on a heated table to maintain body temperature at 37°C. A carotid artery was cannulated to measure blood pressure, and two catheters were inserted into a jugular vein, one for infusion (10 ml h-l kg body wt-l) of either a salt solution (140 mM NaCl, 4 mM KCl; microperfusion experiments) or a glucose solution (275 mM; clearance experiments) and the other to administer supplementary Inactin if necessary. A tracheostomy was performed. The left kidney was exposed by a flank incision, placed in a plastic cup, and observed under a stereomicroscope at X160. An additional 2 ml of infusion solution were administered during the surgical preparation. Microperfusion experiments. All distal microperfusion experiments were performed on animals fed standard chow and as described previously (7,15). In brief, distal tubules were selected for study if at least two loops were accessible at the kidney surface. They were located by injecting stained (FD & C Blue no. 1; Kohnstamm, New York, NY) saline into a proximal tubule loop and visualizing the dyed solution in the lumen of the distal tubule of the same nephron. A perfusion pipette was placed in the upstream distal loop. The proximal tubule of that
sodiumtrans-
known to affect the rate of distal tubule1 K+ secretion are the concentrations of Na+ and Cl- in the tubule lumen (2, 3, 6, 7, 12, 15). With the Cl- concentration maintained at 100 mM and the tubule fluid flow rate held constant, the greatest sensitivity to changes in luminal Na+ concentration has been observed in perfused rat distal tubules to be in the range ~40 mM (6, 7). In the range >40 mM, increases in luminal Na+ have little effect on K+ secretion. The apparent Michaelis constant of this relationship is 11 mM (6). Distal K+ secretion also responds to changes in the luminal concentration of Cl- (2, 3, 6, 12, 15). Microperfusion experiments in which the luminal Cl- concentration was reduced to levels
