Regulation of Na+ channels by luminal Na+ in rat cortical collecting tubule.
1. The idea that luminal Na+ can regulate epithelial Na+ channels was tested in the cortical collecting tubule of the rat using whole-cell and single-channel recordings. Here we report results consistent with the idea of Na+ self-inhibition. 2. Macroscopic amiloride-sensitive currents (INa) were measured by conventional whole-cell clamp. INa was a saturable function of external Na+ concentration ([Na+]o) with an apparent Km of 9 mM. Single channel currents (iNa) were measured in cell-attached patches. iNa increased with pipette Na+ concentration with an apparent Km of 48 mM. Since INa = (iNa)NPo, the different Km values imply that the channel density (N) and/or open probability (Po) increase as [Na+]o decreases. Reduction of [Na+]o after increasing intracellular Na+ concentration also increased the outward amiloride-sensitive conductance, consistent with activation of the Na+ channels. 3. The underlying mechanism was studied by changing pipette Na+ concentration while recording from cell-attached patches. No increase in NPo was observed, suggesting that the effect is not a direct interaction between [Na+]o and the channel. 4. [Na+]o was varied outside the patch-clamp pipette while recording from cell-attached patches. When amiloride was in the bath to prevent Na+ entry, no change in NPo was observed. 5. Activation of the channels by hyperpolarization was observed with 140 mM Na+o but not with 14 mM Na+o. 6. The results are consistent with the concept of self-inhibition of Na+ channels by luminal Na+. Activation of the channels by lowering [Na+]o is not additive with that achieved by hyperpolarization.
Palmer
L G
LG
Department of Physiology and Biophysics, Cornell University Medical College, New York, NY 10021, USA. lgpalmer@med.cornell.edu
Sackin
H
H
Frindt
G
G
D000227:Adenine Nucleotides / Q000494:pharmacology; D000818:Animals; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D006150:Guanine Nucleotides / Q000494:pharmacology; D007672:Kidney Cortex / Q000187:drug effects / Q000502:physiology*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000502:physiology*; D015222:Sodium Channels / Q000187:drug effects / Q000502:physiology*
D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D015222:Sodium Channels; D012964:Sodium