Cyclic Nucleotide - gated Channels on the Flagellum Control Ca 2 1 Entry into Sperm

Cyclic nucleotide-gated (CNG) channels are key elements of cGMPand cAMP-signaling pathways in vertebrate photoreceptor cells and in olfactory sensory neurons, respectively. These channels form heterooligomeric complexes composed of at least two distinct subunits ( a and b ). The a subunit of cone photoreceptors is also present in mammalian sperm. Here we identify one short and several long less abundant transcripts of b subunits in testis. The a and b subunits are expressed in a characteristic temporal and spatial pattern in sperm and precursor cells. In mature sperm, the a subunit is observed along the entire flagellum, whereas the short b subunit is restricted to the principal piece of the flagellum. These findings suggest that different forms of CNG channels coexist in the flagellum. Confocal microscopy in conjunction with the Ca 2 1 indicator Fluo-3 shows that the CNG channels serve as a Ca 2 1 entry pathway that responds more sensitively to cGMP than to cAMP. Assuming that CNG channel subtypes differ in their Ca 2 1 permeability, dissimilar localization of a and b subunits may give rise to a pattern of Ca 2 1 microdomains along the flagellum, thereby providing the structural basis for control of flagellar bending waves.