ATP-sensitive K+-selective channels of inner medullary collecting duct cells

S. C. Sansom, T. Mougouris, S. Ono, T. D. DuBose

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K+-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K+-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K+-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg2+-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+. In addition, a reduction in internal pH from 7.4 to 6.8 had no effect on the activity of either channel. It is concluded that the apical membrane of mIMCD-3 cells contains both a small K+-selective channel that is inhibited by physiological concentrations of ATP and a large K+-selective channel that is activated by Mg2+-ATP.

Original languageEnglish (US)
Pages (from-to)F489-F496
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Volume267
Issue number3 36-3
StatePublished - Jan 1 1994

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Adenosine Triphosphate
Baths
Large-Conductance Calcium-Activated Potassium Channels
Membranes
Cell Line

Keywords

  • mIMCD-3 cell line
  • patch clamp
  • potassium channel

ASJC Scopus subject areas

  • Physiology

Cite this

ATP-sensitive K+-selective channels of inner medullary collecting duct cells. / Sansom, S. C.; Mougouris, T.; Ono, S.; DuBose, T. D.

In: American Journal of Physiology - Renal Fluid and Electrolyte Physiology, Vol. 267, No. 3 36-3, 01.01.1994, p. F489-F496.

Research output: Contribution to journalArticle

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N2 - The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K+-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K+-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K+-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg2+-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+. In addition, a reduction in internal pH from 7.4 to 6.8 had no effect on the activity of either channel. It is concluded that the apical membrane of mIMCD-3 cells contains both a small K+-selective channel that is inhibited by physiological concentrations of ATP and a large K+-selective channel that is activated by Mg2+-ATP.

AB - The inner medullary collecting duct (IMCD) in vivo has the capacity to either secrete or reabsorb K+. However, a selective K+ conductance has not been described previously in the IMCD. In the present study, the patch-clamp method was used to determine the presence and properties of K+-selective channels in the apical membrane of the inner medullary collecting duct cell line, mIMCD-3. Two types of K+-selective channels were observed in both cell-attached and excised patches. The most predominant K+ channel, a smaller conductance K+ channel (SK), was present in cell-attached patches with 140 mM KCl (high bath K+) but not with 135 mM NaCl plus 5 mM KCl (low bath K+) in the bathing solution. The single-channel conductance of SK was 36 pS with inward currents and 29 pS with outward currents in symmetrical 140 mM KCl. SK was insensitive to both voltage and Ca2+. However, SK was inhibited significantly by millimolar concentrations of ATP in excised patches. A second K+-selective channel [a larger K+ channel (BK)] displayed a single-channel conductance equal to 132 pS with inward currents and 90 pS with outward currents in symmetrical 140 mM KCl solutions. BK was intermittently activated in excised inside-out patches by Mg2+-ATP in concentrations from 1 to 5 mM. With complete removal of Mg2+, BK was insensitive to ATP. BK was also insensitive to potential and Ca2+ and was observed in cell-attached patches with 140 mM KCl in the bath solution. Both channels were blocked reversibly by 1 mM Ba2+ from the intracellular surface but not by external Ba2+. In addition, a reduction in internal pH from 7.4 to 6.8 had no effect on the activity of either channel. It is concluded that the apical membrane of mIMCD-3 cells contains both a small K+-selective channel that is inhibited by physiological concentrations of ATP and a large K+-selective channel that is activated by Mg2+-ATP.

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