TY - JOUR
T1 - Reabsorption of betaine in Henle's loops of rat kidney in vivo
AU - Pummer, Stefan
AU - Dantzler, William H.
AU - Lien, Yeong Hau H.
AU - Moeckel, Gilbert W.
AU - Völker, Katharina
AU - Silbernagl, Stefan
PY - 2000/3
Y1 - 2000/3
N2 - This study was designed 1) to localize and 2) to characterize betaine reabsorption from the tubular lumen in rat kidney in vivo, and 3) to test whether reabsorption is modulated by the diuretic state. [14C]betaine (+ [3H]inulin) was microperfused through the proximal convoluted tubule (PCT) and microinfused into late proximal (LP) and early distal (ED) tubules, long loops of Henle (LLH), and vasa recta of the rat in vivo et situ, and the fractional recovery of the 14C label was determined endproximally (PCT) and in the final urine, respectively. [14C]betaine was not reabsorbed during ED microinfusion, whereas fractional reabsorption during LP microinfusion was 82% at 0.06 mM betaine and decreased gradually to 4.8% at 60 mM. L-Proline had lower Michaelis-Menten constant (K(m)) and sarcosine a higher K(m) than betaine. Chronic, but not acute, diuresis inhibited betaine reabsorption in Henle's loops. Fractional [14C]betaine reabsorption in PCT was much smaller than that during LP microinfusion. [14C]betaine (7.28 mM) microinfused 1) into LLH was reabsorbed to 30% and 2) into vasa recta appeared in the ipsilateral urine to a much higher extent than contralaterally. In both cases, no saturation was detected at 70 mM. We conclude that betaine is reabsorbed by mediated transport from descending limbs of short Henle's loops by a proline-preferring carrier in a diuresis-modulated manner. In the deep medulla, bidirectional blood/urine betaine transport exists.
AB - This study was designed 1) to localize and 2) to characterize betaine reabsorption from the tubular lumen in rat kidney in vivo, and 3) to test whether reabsorption is modulated by the diuretic state. [14C]betaine (+ [3H]inulin) was microperfused through the proximal convoluted tubule (PCT) and microinfused into late proximal (LP) and early distal (ED) tubules, long loops of Henle (LLH), and vasa recta of the rat in vivo et situ, and the fractional recovery of the 14C label was determined endproximally (PCT) and in the final urine, respectively. [14C]betaine was not reabsorbed during ED microinfusion, whereas fractional reabsorption during LP microinfusion was 82% at 0.06 mM betaine and decreased gradually to 4.8% at 60 mM. L-Proline had lower Michaelis-Menten constant (K(m)) and sarcosine a higher K(m) than betaine. Chronic, but not acute, diuresis inhibited betaine reabsorption in Henle's loops. Fractional [14C]betaine reabsorption in PCT was much smaller than that during LP microinfusion. [14C]betaine (7.28 mM) microinfused 1) into LLH was reabsorbed to 30% and 2) into vasa recta appeared in the ipsilateral urine to a much higher extent than contralaterally. In both cases, no saturation was detected at 70 mM. We conclude that betaine is reabsorbed by mediated transport from descending limbs of short Henle's loops by a proline-preferring carrier in a diuresis-modulated manner. In the deep medulla, bidirectional blood/urine betaine transport exists.
KW - Betaine transport
KW - In vivo microinfusion
KW - Organic osmolytes
KW - Rat kidney
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U2 - 10.1152/ajprenal.2000.278.3.f434
DO - 10.1152/ajprenal.2000.278.3.f434
M3 - Article
C2 - 10710548
AN - SCOPUS:0034020955
SN - 1931-857X
VL - 278
SP - F434-F439
JO - American Journal of Physiology - Renal Physiology
JF - American Journal of Physiology - Renal Physiology
IS - 3 47-3
ER -