CNG channels could be involved in some form of motility control and even in chemotactic swimming behavior or in the acrosomal exocytosis. However, a receptor-type GC in mammalian sperm has yet to be identified. Mouse sperm express other channels such as CatSper1. Male sterility can be accomplished by disrupting the CatSper1 gene; additionally, the cAMP-induced calcium influx is abolished in mutant mice. Although CatSper need additional subunits to become functional, they are unrelated to CNG channels because CatSper lacks a cAMP/cGMP-binding site. It is possible that CNG and CatSper subunits assemble to form calcium-permeable and cyclic nucleotide-sensitive ion channels. Kidney cGMP-sensitive channels have been analyzed in the renal medulla, specifically in collecting duct cells, which influence the body's electrolyte and fluid balance. CNG channel activity is controlled by the interaction between cGMP-dependent protein kinase and G1 protein because of cGMP's involvement in phosphorylation mechanisms. In the cells from an inner medullary collecting duct, CNG channels exhibit cation selectivity unit conductance, calcium permeability, and pharmacology very similar to cyclic nucleotide-gated ion channels. A stimulant, atrial natriuretic factor (ANF) increases cGMP production in the kidneys, which increases function of the glomerulus by a combination of relaxing and contracting arterioles. Differences between retinal and renal cDNA have been implicated in the functional differences between CNG channels in these two tissues. Gonadotropin-releasing hormone There has been identification of CNG ion channel subunits A2, A4, and B1 in a neuronal cell line that secretes gonadotropin-releasing hormone (GrH). The three subunits make up the CNG channels on chemosensitive cilia of OSNs. In high extracellular calcium, the unit conductance of CNG channels in rods and OSNs are significantly smaller than those measured in the neuronal line. It seems doubtful that CNG channels would create large unit conductance. Plants CNG ions channels in plants are similar in amino acid sequence and structure to non-selective cation CNG channels in animals, as well as trans-membrane-domain K+-selective shaker family channels. However, there are drastic differences that are seen exclusively in plant CNG channels. The amino acid sequence of the pore sequence in plant CNG channels lacks the selectivity filter found in animal CNG channels as well as lacks a glycine-tyrosine-glycine-aspartate (GYGD) motif in the K+-selectivity filter sequence. Other sequence differences are seen in plant CNG channels, particularly in the cyclic nucleotide binding domain (CNBD). In plants, the Calmodulin binding domain (CaMBD) is found to overlap α-helix C in the CNBD of