Whole cell and unitary amiloride-sensitive sodium currents in M-1 mouse cortical collecting duct cells.
Amiloride-sensitive whole cell currents have been reported in M-1 mouse cortical collecting duct cells (Korbmacher et al., J. Gen. Physiol. 102: 761-793, 1993). We have confirmed that amiloride inhibits the whole cell currents but not necessarily the measured whole cell currents. Anomalous responses were eliminated by removing external Na+ and/or introducing paraepithelial shunts. The amiloride-sensitive whole cell currents displayed Goldman rectification. The ionic selectivity sequence of the amiloride-sensitive conductance was Li+ > Na+ >> K+. Growth of M-1 cells on permeable supports increased the amiloride-sensitive whole cell permeability, compared with cells grown on plastic. Single amiloride-sensitive channels were observed, which conformed to the highly selective low-conductance amiloride-sensitive class [Na(5)] of epithelial Na+ channels. Hypotonic pretreatment markedly slowed run-down of channel activity. The gating of the M-1 Na+ channel in excised patches was complex. Open- and closed-state dwell-time distributions from patches that display one operative channel were best described with two or more exponential terms each. We conclude that 1) study of M-1 whole cell Na+ currents is facilitated by reducing the transepithelial potential to zero, 2) these M-1 currents reflect the operation of Na(5) channels, and 3) the Na+ channels display complex kinetics, involving > or = 2 open and > or = 2 closed states.
Chalfant
M L
ML
Lankenau Medical Research Center, Wynnewood 19096, USA.
O'Brien
T G
TG
Civan
M M
MM
D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D002712:Chlorides / Q000494:pharmacology; D003584:Cytological Techniques; D004553:Electric Conductivity; D007038:Hypotonic Solutions / Q000494:pharmacology; D007552:Isotonic Solutions / Q000494:pharmacology; D007672:Kidney Cortex; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D008536:Meglumine / Q000494:pharmacology; D051379:Mice; D000077331:Ringer's Solution; D012964:Sodium / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology
D002712:Chlorides; D007038:Hypotonic Solutions; D007552:Isotonic Solutions; D012965:Sodium Chloride; D008536:Meglumine; D000584:Amiloride; D000077331:Ringer's Solution; D012964:Sodium