Non-selective cation channels, which are permeable to monovalent and divalent cations, are expressed in various tissues. cDNAs encoding cGMP-gated cation channels (cGCC) have been cloned in retinal rods, cones, heart, and kidneys. cGCC in retinal rods is closed when a level of intracellular cGMP decreased by photon. On the other hand, the cGCC in the kidney IMCD is inhibited by ANP via cGMP. P2X receptors play a role in fast synaptic transmission between neurons. They are the molecules which open on binding to extracellular ATP and allow cations to enter the cell. cDNA encoding P2X receptors from vas deferens and PC12 cells share considerable sequence similarity with rENaC (epithelial Na+ channels) and mechanosensory genes (mec-10) in C. elegans.