Functional mapping of rbOCT1 and rbOCT2 activity in the S2 segment of rabbit proximal tubule

Santi Kaewmokul, Varanuj Chatsudthipong, Kristen K. Evans, William H Dantzler, Stephen Wright

Research output: Contribution to journalArticle

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Abstract

A strategy was developed to determine the distribution of activity mediated by the organic cation (OC) transporters OCT1 and OCT2 in rabbit renal proximal tubule (RPT). Both transporters displayed similar affinities for tetraethylammonium (TEA; in CHO-K1 cells, TEA concentrations that resulted in half-maximal transport were 19.9 and 34.5 μM for OCT1 and OCT2, respectively). Similarly, some OCs showed little capacity to discriminate between the two processes (IC50 values for ephedrine of 13.6 and 24. 2 μM for OCT1 and OCT2, respectively). However, OCT2 had a higher affinity for cimetidine and [2-(4-nitro-2,1,3-benzoxadiazo-7-yl) aminoethyl]trimethylammonium (NBD-TMA; 1.3 and 1.4 μM, respectively) than did OCT1 (97.3 and 108 μM, respectively). Conversely, OCT1 had a higher affinity for tyramine and pindolol than did OCT2 (21.2 and 2.4 vs. 361 and 50 μM, respectively). We designated these as "discriminatory inhibitors" and used them to determine the relative contribution of OCT1 and OCT2 for TEA transport in single S2 segments of rabbit RPT. Cimetidine and NBD-TMA were high-affinity inhibitors of TEA transport in S2 segments (median IC50 values of 12.3 and 1.4 μM, respectively); in comparison, tyramine and pindolol were low-affinity inhibitors (265 and 69.3 μM, respectively). These IC50 values were sufficiently close to those for OCT2 to support the conclusion that TEA transport in the S2 segment of rabbit RPT is dominated by OCT2. However, the profile of inhibition of tyramine (an OCT1-selective substrate) transport in single S2 segments indicated that, despite a comparatively low level of expression, OCT1 can play a dominant role in the uptake of selected OC substrates.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Renal Physiology
Volume285
Issue number6 54-6
StatePublished - Dec 2003

Fingerprint

Proximal Kidney Tubule
Tyramine
Inhibitory Concentration 50
Pindolol
Cimetidine
Rabbits
Cations
Ephedrine
Tetraethylammonium
CHO Cells
2-(4-nitro-2,1,3-benzoxadiazol-7-yl)aminoethyl-trimethylammonium

Keywords

  • Cimetidine
  • Kidney
  • Organic cation
  • Tetraethylammonium
  • Transport

ASJC Scopus subject areas

  • Physiology

Cite this

Functional mapping of rbOCT1 and rbOCT2 activity in the S2 segment of rabbit proximal tubule. / Kaewmokul, Santi; Chatsudthipong, Varanuj; Evans, Kristen K.; Dantzler, William H; Wright, Stephen.

In: American Journal of Physiology - Renal Physiology, Vol. 285, No. 6 54-6, 12.2003.

Research output: Contribution to journalArticle

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abstract = "A strategy was developed to determine the distribution of activity mediated by the organic cation (OC) transporters OCT1 and OCT2 in rabbit renal proximal tubule (RPT). Both transporters displayed similar affinities for tetraethylammonium (TEA; in CHO-K1 cells, TEA concentrations that resulted in half-maximal transport were 19.9 and 34.5 μM for OCT1 and OCT2, respectively). Similarly, some OCs showed little capacity to discriminate between the two processes (IC50 values for ephedrine of 13.6 and 24. 2 μM for OCT1 and OCT2, respectively). However, OCT2 had a higher affinity for cimetidine and [2-(4-nitro-2,1,3-benzoxadiazo-7-yl) aminoethyl]trimethylammonium (NBD-TMA; 1.3 and 1.4 μM, respectively) than did OCT1 (97.3 and 108 μM, respectively). Conversely, OCT1 had a higher affinity for tyramine and pindolol than did OCT2 (21.2 and 2.4 vs. 361 and 50 μM, respectively). We designated these as {"}discriminatory inhibitors{"} and used them to determine the relative contribution of OCT1 and OCT2 for TEA transport in single S2 segments of rabbit RPT. Cimetidine and NBD-TMA were high-affinity inhibitors of TEA transport in S2 segments (median IC50 values of 12.3 and 1.4 μM, respectively); in comparison, tyramine and pindolol were low-affinity inhibitors (265 and 69.3 μM, respectively). These IC50 values were sufficiently close to those for OCT2 to support the conclusion that TEA transport in the S2 segment of rabbit RPT is dominated by OCT2. However, the profile of inhibition of tyramine (an OCT1-selective substrate) transport in single S2 segments indicated that, despite a comparatively low level of expression, OCT1 can play a dominant role in the uptake of selected OC substrates.",
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AU - Wright, Stephen

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AB - A strategy was developed to determine the distribution of activity mediated by the organic cation (OC) transporters OCT1 and OCT2 in rabbit renal proximal tubule (RPT). Both transporters displayed similar affinities for tetraethylammonium (TEA; in CHO-K1 cells, TEA concentrations that resulted in half-maximal transport were 19.9 and 34.5 μM for OCT1 and OCT2, respectively). Similarly, some OCs showed little capacity to discriminate between the two processes (IC50 values for ephedrine of 13.6 and 24. 2 μM for OCT1 and OCT2, respectively). However, OCT2 had a higher affinity for cimetidine and [2-(4-nitro-2,1,3-benzoxadiazo-7-yl) aminoethyl]trimethylammonium (NBD-TMA; 1.3 and 1.4 μM, respectively) than did OCT1 (97.3 and 108 μM, respectively). Conversely, OCT1 had a higher affinity for tyramine and pindolol than did OCT2 (21.2 and 2.4 vs. 361 and 50 μM, respectively). We designated these as "discriminatory inhibitors" and used them to determine the relative contribution of OCT1 and OCT2 for TEA transport in single S2 segments of rabbit RPT. Cimetidine and NBD-TMA were high-affinity inhibitors of TEA transport in S2 segments (median IC50 values of 12.3 and 1.4 μM, respectively); in comparison, tyramine and pindolol were low-affinity inhibitors (265 and 69.3 μM, respectively). These IC50 values were sufficiently close to those for OCT2 to support the conclusion that TEA transport in the S2 segment of rabbit RPT is dominated by OCT2. However, the profile of inhibition of tyramine (an OCT1-selective substrate) transport in single S2 segments indicated that, despite a comparatively low level of expression, OCT1 can play a dominant role in the uptake of selected OC substrates.

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