Cortical collecting duct
cGMP dependent protein kinase
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract 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/ Panion 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 (NP o ). Cytoplasmic application of adenine nucleotides inhibits the M-1 NSC channel. At doses of 10−4 m and 10−3 m, ATP reduces NP o by 23% and 69%, respectively. Furthermore, since ADP (10−3 m) reduces NP o by 93%, the inhibitory effect of adenine nucleotides is not dependent on the presence of a γ-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 NP o by 35% at depolarizing voltages and by 80% at hyperpolarizing voltages. We conclude that the NSC 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.
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