ATP-sensitive K(+)-selective channels of inner medullary collecting duct cells.
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 Mg(2+)-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+.(ABSTRACT TRUNCATED AT 250 WORDS)
Sansom
S C
SC
Department of Medicine, University of Texas, Houston 77030.
Mougouris
T
T
Ono
S
S
DuBose
T D
TD
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002460:Cell Line; D007679:Kidney Medulla; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000145:classification / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats
D015221:Potassium Channels; D001464:Barium; D000255:Adenosine Triphosphate