Voltage dependence of calcium transport in the thick ascending limb of Henle's loop

1979 ◽  
Vol 236 (4) ◽  
pp. F357-F364 ◽  
Author(s):  
J. E. Bourdeau ◽  
M. B. Burg
Keyword(s):  
Calcium Transport ◽  
Calcium Absorption ◽  
Calcium Flux ◽  
Thick Ascending Limb ◽  
Sodium Permeability ◽  
Calcium Fluxes ◽  
Henle's Loop ◽  
Wide Range ◽  
Net Flux

Thick ascending limbs of Henle's loop were dissected from rabbit kidneys and perfused in vitro. Unidirectional transepithelial calcium fluxes from lumen-to-bath and bath-to-lumen were measured with 45Ca using different solutions that caused the transepithelial voltage to vary over a wide range. With lumen-positive voltages there was net calcium absorption from lumen to bath which varied directly with the voltage. With voltage near zero there was no measurable net flux. When the voltage was made negative, the direction of net calcium transport reversed (i.e., secretion from bath to lumen). The presence or absence of bicarbonate in the lumen did not affect the calcium fluxes. Calcium permeability, calculated from the dependence of net flux on voltage, was 7.7 x 10(-6) cm/s, which is approximately 25% of the sodium permeability previously determined in this segment. Analysis of the calcium flux ratios revealed interdependence of the bidirectional fluxes consistent with single-file diffusion but no evidence for active calcium transport. We conclude that there is an important component of passive net calcium transport driven by the voltage in this segment.

Effect of PTH on calcium transport across the cortical thick ascending limb of Henle's loop

1980 ◽  
Vol 239 (2) ◽  
pp. F121-F126 ◽  
Author(s):  
J. E. Bourdeau ◽  
M. B. Burg
Keyword(s):  
Adrenocorticotropic Hormone ◽  
Calcium Absorption ◽  
Calcium Flux ◽  
Thick Ascending Limb ◽  
Henle's Loop ◽  
Transepithelial Voltage ◽  
Net Flux ◽  
Stimulation Of

Cortical thick ascending limbs of Henle's loop were dissected from rabbit kidneys and perfused in vitro. Unidirectional transepithelial calcium fluxes from lumen-to-bath and bath-to-lumen were measured with 45Ca. The tubules were bathed in 150 mM sodium and perfused with 60 mM sodium to simulate conditions in the cortical thick ascending limb in vivo. During the 20-30 min preceding the addition of parathyroid hormone (PTH), net calcium absorption decreased from 0.207 to 0.084 pmol x s-1 x cm-1. After addition of synthetic bovine PTH (60-64 nM) to the bath, there was an immediate increase in calcium absorption, and by 20 min the net flux increased to 0.415 pmol x s-1 x cm-1. The increase in calcium absorption was due to an increase in the lumen-to-bath flux. Dibutyryl-cAMP or 8-BrcAMP mimicked PTH; adrenocorticotropic hormone had no effect on the calcium flux. Transepithelial voltage was unchanged after addition of PTH. We conclude that PTH increases calcium absorption across the cortical thick ascending limb, probably by stimulation of adenylate cyclase.

Voltage-dependent calcium movement across the cortical collecting duct

1982 ◽  
Vol 242 (3) ◽  
pp. F285-F292 ◽  
Author(s):  
J. E. Bourdeau ◽  
R. J. Hellstrom-Stein
Keyword(s):  
Calcium Transport ◽  
Collecting Duct ◽  
Calcium Flux ◽  
Thick Ascending Limb ◽  
Cortical Collecting Duct ◽  
Loop Analysis ◽  
Wide Range ◽  
Transepithelial Voltage ◽  
Net Flux ◽  
Calcium Permeability

Cortical collecting ducts were dissected from rabbit kidneys and perfused in vitro. Unidirectional transepithelial calcium fluxes from bath-to-lumen and lumen-to-bath were measured with 45Ca. Transepithelial voltage was varied over a wide range by pharmacologic manipulations. With lumen-negative voltages net calcium secretion from bath to lumen, which varied directly with the voltage, was observed. At voltages near 0 there was no measurable net flux. When the voltage was made positive, the direction of net calcium transport reversed (i.e., absorption from lumen to bath). Calcium permeability, calculated from the dependence of net flux on voltage, was 1.4 X 10(-7) cm/s, which is less than 2% of the calcium permeability previously determined in the cortical thick ascending limb of Henle's loop. Analysis of the calcium flux ratios revealed apparent interdependence of the bidirectional fluxes consistent with exchange diffusion but no evidence for active calcium transport. We conclude that there is a small, but measurable, component of passive net calcium flux driven by the transepithelial voltage across the cortical collecting duct.

Ca fluxes across duodenum and colon of spontaneously hypertensive rats: effect of 1,25(OH)2D3

1986 ◽  
Vol 251 (2) ◽  
pp. F278-F282 ◽  
Author(s):  
U. Gafter ◽  
S. Kathpalia ◽  
D. Zikos ◽  
K. Lau
Keyword(s):  
Calcium Transport ◽  
Spontaneously Hypertensive Rats ◽  
Calcium Absorption ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Calcium Flux ◽  
Hypertensive Rats ◽  
Spontaneously Hypertensive ◽  
Wistar Kyoto

Calcium absorption by spontaneously hypertensive rats (SHR) was variably reported to be different from normotensive Wistar-Kyoto (WKY) controls. Furthermore, blunted responsiveness to the intestinal effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been postulated. To evaluate this hypothesis, calcium fluxes were measured by the Ussing technique across duodenum and descending colon with or without prior 1,25(OH)2D3 treatment. Duodenal mucosal-to-serosal calcium flux (Jm----s) (44.9 vs. 52.4 nmol X cm-2 X h-1), serosal-to-mucosal flux (Js----m) (25.6 vs. 28.4 nmol X cm-2 X h-1), and net flux (Jnet) were comparable. 1,25(OH)2D3 increased duodenal Jm----s in both SHR and WKY groups (95.2 and 86.8 nmol X cm-2 X h-1). Js----m was lower in SHR (26.1 vs. 35.6 nmol X cm-2 X h-1, P less than 0.01), although the tendency for a higher Jnet in SHR (68.6 vs. 51.2 nmoles X cm-2 X h-1) was statistically insignificant. Short-circuit current was higher in the colon of SHR, both before and after 1,25(OH)2D3, suggesting increased sodium transport. Basal colonic Jnet was virtually zero in both groups but comparably increased by 1,25(OH)2D3 because of stimulation in only Jm----s. Prevention of hypertension by hydralazine since the 4th wk of age did not alter the findings compared with the hypertensive SHR, suggesting calcium transport rates were unaffected by hypertension. These data indicate that in vitro, duodenal, and colonic active calcium transport by the SHR is similar to WKY. Their normal responses to 1,25(OH)2D3 do not support the hypothesis of intestinal resistance.

Glucose enhancement of transcellular calcium transport in the intestine

1988 ◽  
Vol 255 (3) ◽  
pp. G339-G345 ◽  
Author(s):  
K. M. Carroll ◽  
R. J. Wood ◽  
E. B. Chang ◽  
I. H. Rosenberg
Keyword(s):  
Calcium Transport ◽  
Calcium Uptake ◽  
Calcium Absorption ◽  
Membrane Integrity ◽  
Calcium Flux ◽  
Calcium Efflux ◽  
Cell Membrane Integrity ◽  
Active Calcium ◽  
Altered Cell

Glucose stimulates calcium transport in vitro in rat duodenal tissue and isolated enterocytes. Under short-circuited conditions, glucose increased mucosal to serosal calcium flux (JCa(m----s)) without altering serosal to mucosal calcium flux (JCa(s----m)) in the duodenum, the primary site of active calcium absorption in the rat small intestine. The half-maximal dose (ED50) of the glucose stimulatory effect was less than 1 mM, and an increase in JCa(m----s) of 80% over control was seen at a glucose concentration of 50 mM. Glucose did not increase calcium flux in the ileum where active calcium absorption is minimal. Glucose stimulated net calcium uptake by 35% in isolated duodenal enterocytes. Glucose did not alter calcium efflux from preloaded enterocytes suspended in calcium-free buffer. Glucose enhancement of net calcium uptake in enterocytes was not caused by altered cell membrane integrity or functional viability. The nonmetabolizable glucose analogue alpha-methylglucoside did not stimulate calcium transport. Our findings suggest that glucose can stimulate intestinal calcium absorption, at least partially, by enhancing transcellular calcium transport and that cellular glucose metabolism is necessary for stimulation of this route of calcium transport.

Transepithelial calcium transport by rat cecum: high-efficiency absorptive site

1981 ◽  
Vol 240 (6) ◽  
pp. G424-G431 ◽  
Author(s):  
H. N. Nellans ◽  
R. S. Goldsmith
Keyword(s):  
Calcium Transport ◽  
High Efficiency ◽  
Calcium Absorption ◽  
Short Circuit ◽  
Calcium Fluxes ◽  
Calcium Diet ◽  
Low Calcium Diet ◽  
High Calcium ◽  
Rat Cecum

Transepithelial calcium transport has been investigated in rat cecum under in vitro voltage-clamp conditions. Under short-circuit conditions, the cecum behaves as a relatively tight epithelium for calcium fluxes, where mucosal-to-serosal (JCam leads to s) flux exceeds the reverse flux by at least 15-fold. JCanet is abolished in the presence of 1 mM N-ethylmaleimide, is inhibited by 40% with 1 mM ouabain, and is decreased by at least 60% when medium sodium is replaced by choline. Voltage-clamping experiments suggest that both electroneutral- and electrogenic-mediated calcium fluxes traverse the cell in the mucosal-to-serosal direction. Serosal-to-mucosal flux is purely diffusional and probably constrained to the paracellular pathway. In rats weighing less than 175 g, a low-calcium diet has no significant stimulatory effect on JCam leads to s, but a high-calcium diet markedly reduces this flux. These results suggest that the cecum possesses the highest density of calcium transport sites in the rat intestine and is ideally suited for bulk calcium absorption, which may be “down regulated” in response to an increased calcium load in growing animals.

Calcium transport in turtle bladder

1987 ◽  
Vol 253 (6) ◽  
pp. R917-R921
Author(s):  
S. Sabatini ◽  
N. A. Kurtzman
Keyword(s):  
Calcium Transport ◽  
Calcium Absorption ◽  
Short Circuit ◽  
Open Circuit ◽  
Calcium Flux ◽  
Bladder Epithelium ◽  
Control Value ◽  
Sodium Calcium ◽  
Turtle Bladder ◽  
Absorptive Flux

Unidirectional 45Ca fluxes were measured in the turtle bladder under open-circuit and short-circuit conditions. In the open-circuited state net calcium flux (JnetCa) was secretory (serosa to mucosa) and was 388.3 +/- 84.5 pmol.mg-1.h-1 (n = 20, P less than 0.001). Ouabain (5 X 10(-4) M) reversed JnetCa to an absorptive flux (serosal minus mucosal flux = -195.8 +/- 41.3 pmol.mg-1.h-1; n = 20, P less than 0.001). Amiloride (1 X 10(-5) M) reduced both fluxes such that JnetCa was not significantly different from zero. Removal of mucosal sodium caused net calcium absorption; removal of serosal sodium caused calcium secretion. When bladders were short circuited, JnetCa decreased to approximately one-third of control value but remained secretory (138.4 +/- 54.3 pmol.mg-1.h-1; n = 9, P less than 0.025). When ouabain was added under short-circuit conditions, JnetCa was similar in magnitude and direction to ouabain under open-circuited conditions (i.e., absorptive). Tissue 45Ca content was approximately equal to 30-fold lower when the isotope was placed in the mucosal bath, suggesting that the apical membrane is the resistance barrier to calcium transport. The results obtained in this study are best explained by postulating a Ca2+-ATPase on the serosa of the turtle bladder epithelium and a sodium-calcium antiporter on the mucosa. In this model, the energy for calcium movement would be supplied, in large part, by the Na+-K+-ATPase. By increasing cell sodium, ouabain would decrease the activity of the mucosal sodium-calcium exchanger (or reverse it), uncovering active calcium transport across the serosa.

Na-K-ATPase activity along the rabbit, rat, and mouse nephron

1979 ◽  
Vol 237 (2) ◽  
pp. F114-F120 ◽  
Author(s):  
A. I. Katz ◽  
A. Doucet ◽  
F. Morel
Keyword(s):  
Atpase Activity ◽  
Thick Ascending Limb ◽  
Sensitivity Limit ◽  
Henle's Loop ◽  
Collecting Tubule ◽  
Pars Recta ◽  
Hydrolysis Of ◽  
Total Enzyme

Na-K-ATPase activity along the rabbit, rat, and mouse nephron was determined with a micromethod that measures directly labeled phosphate released by the hydrolysis of [gamma-32P]ATP. Na-K-ATPase activity was highest in the rat, intermediate in the mouse, and lowest in the rabbit nephron. With the exception of rabbit cortical thick ascending limb, the enzyme profile was similar in the three species: Na-K-ATPase activity per millimeter tubule length was highest in the distal convoluted tubule and thick ascending limb of Henle's loop, intermediate in the proximal convoluted tubule, and lowest in the pars recta and collecting tubule. The enzyme was present in the thin limbs of Henle's loop, but its activity was very low and measurements were close to the sensitivity limit of the method. Both the absolute activity and the fraction of the total enzyme represented by Na-K-ATPase were severalfold higher than in kidney homogenates. Finally, the Na-K-ATPase activity measured in certain segments of the rat and rabbit nephron in this study seems sufficient to account in theory for the active component of the net sodium transport found in the corresponding region of the nephron with either in vivo or in vitro single tubule microperfusion techniques.

Effect of hypophysectomy on calcium transport by rat duodenum.

1977 ◽  
Vol 232 (2) ◽  
pp. E229
Author(s):  
E L Krawitt ◽  
A S Kunin ◽  
H W Sampson ◽  
B F Bacon
Keyword(s):  
Calcium Transport ◽  
Calcium Absorption ◽  
Plasma Flux ◽  
Perfusion Technique ◽  
Intestinal Length ◽  
Absorption Studies ◽  
Luminal Perfusion ◽  
Rat Duodenum

To examine the effect of hypophysectomy on intestinal calcium absorption, studies were performed on immature rats 7, 14, and 21 days after hypophysectomy. Duodenal calcium transport was measured in vitro utilizing everted gut sacs and in vivo by a luminal perfusion technique. Hypophysectomy produced no differences in the ability of everted gut sacs to transport calcium. Similarly, when in vivo transport data were expressed on the basis of intestinal length, no significant differences were noted. However, when transport data were expressed on the basis of mucosal weight, increases in absorption and lumen-to-plasma fluxes were apparent in hypophysectomized animals. No differences were seen in plasma-to-lumen fluxes. The results indicate that when the transport data are corrected for mass of intestinal mucosa, the duodenum from hypophysectomized animals absorbs calcium more avidly due to an increase in lumen-to-plasma flux.

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