MOUSE CORTICAL COLLECTING DUCT CELLS SHOW NONSELECTIVE CATION CHANNEL ACTIVITY AND EXPRESS A GENE RELATED TO THE CGMP-GATED ROD PHOTORECEPTOR CHANNEL

Apical nonselective cation channels with an average single-channel conductance of 34 +/- 2.3 pS were found in M-1 mouse cortical collecting duct cells. Channel activity is increased by depolarization and abolished by cytoplasmic calcium removal. Cytoplasmic application of 0.1 mM cGMP decreases channel open probability by 27%. cDNAs corresponding to almost-equal-to 40% of the coding region of the photoreceptor channel were isolated by the polymerase chain reaction from M-1 cells and a rat kidney cDNA library. The rat kidney-derived sequence differs by a single base, and the M-1-cell-derived sequence differs by only two bases, from the photoreceptor sequence. A second clone from M-1 cells differs by 20 out of 426 bases from the photoreceptor sequence. In all three clones, the deduced amino acid sequence is identical to that of the rat photoreceptor channel. Northern blot analysis of poly(A)+ RNA from M-1 cells reveals the presence of a 3.2-kilobase band hybridizing with a retinal cGMP-gated cation channel probe. The results suggest the expression in M-1 cells of more than one gene coding for nonselective cation channels or channel subunits, one of which is identical to the cGMP-gated cation channel gene of rod photoreceptors.