Cyclic nucleotide-gated cation channels mediate sodium absorption by IMCD (mIMCD-K2) cells.
The inner medullary collecting duct cell line, mIMCD-K2, absorbs Na+ by an amiloride-sensitive, electrogenic mechanism. The goal of the present study was to characterize the amiloride-sensitive, Na+ -conducting channels responsible for electrogenic Na+ absorption. To this end, we measured Na+ currents in single cells with the patch-clamp technique and Na+ currents across monolayers mounted in Ussing-type chambers. In whole cell patch-clamp experiments, amiloride-sensitive, inward Na+ currents were mediated by nonselective cation channels. In single-channel patch-clamp experiments, amiloride- and guanosine 3',5'-cyclic monophosphate (cGMP)-sensitive, 20-pS nonselective cation channels (i.e., CNG channels) were identified in the apical membrane. CNG channels were inhibited by amiloride, diltiazem, ethylisopropylamiloride (EIPA), and 8-bromo-cGMP and were permeable to Ca2+ and Mg2+. Epithelial Na+ channels were never observed in whole cell or single-channel recordings. Na+ absorption across confluent monolayers was inhibited with a rank order potency of benzamil > amiloride > phenamil >> EIPA > diltiazem. Our data are most consistent with the view that CNG channels mediate electrogenic Na+ absorption across mIMCD-K2 cells.
Vandorpe
D H
DH
Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
Ciampolillo
F
F
Green
R B
RB
Stanton
B A
BA
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000502:physiology; D002999:Clone Cells; D006152:Cyclic GMP / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D015640:Ion Channel Gating; D007473:Ion Channels / Q000502:physiology*; D007679:Kidney Medulla / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000502:physiology*; D008274:Magnesium / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008969:Molecular Sequence Data; D009712:Nucleotides, Cyclic / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000502:physiology
D007473:Ion Channels; D009712:Nucleotides, Cyclic; D015222:Sodium Channels; D000584:Amiloride; D012964:Sodium; D004110:Diltiazem; D006152:Cyclic GMP; D008274:Magnesium; D002118:Calcium; C039614:ethylisopropylamiloride