A calcium-activated and nucleotide-sensitive nonselective cation channel in M-1 mouse cortical collecting duct cells.
We recently reported that M-1 mouse cortical collecting duct cells show nonselective cation (NSC) channel activity (Proc. Natl. Acad. Sci. USA 89:10262-10266, 1992). In this study, we further characterize the M-1 NSC channel using single-channel current recordings in excised inside-out patches. The M-1 NSC channel does not discriminate between Na+, K+, Rb+, Cs+, and Li+. It has a linear I-V relation with a conductance of 22.7 +/- 0.5 pS (n = 78) at room temperature. The Pcation/P(anion) ratio is about 60 and there is no measurable conductance for NMDG, Ca2+, Ba2+, and Mn2+. Cytoplasmic calcium activates the M-1 NSC channel at a threshold of 10(-6) M and depolarization increases channel activity (NPo). Cytoplasmic application of adenine nucleotides inhibits the M-1 NSC channel. At doses of 10(-4) M and 10(-3) M, ATP reduces NPo by 23% and 69%, respectively. Furthermore, since ADP (10(-3) M) reduces NPo by 93%, the inhibitory effect of adenine nucleotides is not dependent on the presence of a gamma-phosphoryl group and therefore does not involve protein phosphorylation. The channel is not significantly affected by 8-Br-cGMP (10(-4) M) or by cGMP-dependent protein kinase (10(-7) M) in the presence of 8-Br-cGMP (10(-5) M) and ATP (10(-4) M). The NSC channel is not sensitive to amiloride (10(-4) M cytoplasmic and/or extracellular) but flufenamic acid (10(-4) M) produces a voltage-dependent block, reducing NPo by 35% at depolarizing voltages and by 80% at hyperpolarizing voltages. We conclude that the NCS channel of M-1 mouse cortical collecting duct cells belongs to an emerging family of calcium-activated and nucleotide-sensitive nonselective cation channels. It does not contribute to amiloride-sensitive sodium absorption and is unlikely to be a major route for calcium entry. The channel is normally quiescent but may be activated under special physiological conditions, e.g., during volume regulation.
Korbmacher
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C
Zentrum der Physiologie, Johann Wolfgang Goethe Universität, Frankfurt am Main, FRG.
Volk
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T
Segal
A S
AS
Boulpaep
E L
EL
Frömter
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E
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D007473:Ion Channels / Q000502:physiology*; D007672:Kidney Cortex / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism; D051379:Mice; D009711:Nucleotides / Q000494:pharmacology; D018408:Patch-Clamp Techniques
D007473:Ion Channels; D009711:Nucleotides; D002118:Calcium