Molecular diversity of cyclic nucleotide-gated cation channels.

Cyclic nucleotide-gated cation channels (CNG channels) form a multi-gene family consisting of at least five distinct members (CNG1-5). Expression studies have indicated that only CNG1-3 are able to form functional homooligomeric channels. Although structurally related, the cDNAs of CNG4-5 fail to induce cyclic nucleotide-dependent currents when expressed alone. However, when co-expressed with CNG1-3 they confer some of the physiologically observed properties of native CNG channels which are absent from the homooligomeric CNG1-3 channels. CNG channels are expressed in several tissues and cell types pointing to a general function of these channels in a wide variety of cellular systems. There is now increasing evidence that a major function of CNG channels may consist in providing a second messenger-regulated pathway for Ca2+ influx.