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J. Cell Biol.,
Volume 142, Number 2, July 27, 1998 473-484
* Forschungsinstitut für Molekulare Pharmakologie, D-10315 Berlin; Cyclic nucleotide-gated (CNG) channels are
key elements of cGMP- and 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 ( Institut für Biologische Informationsverarbeitung,
Forschungszentrum Jülich, D-52425 Jülich; and § Anatomisches Institut, Universitätskrankenhaus Eppendorf, D-20246 Hamburg
and 
). The subunit of cone
photoreceptors is also present in mammalian sperm.
Here we identify one short and several long less abundant transcripts of subunits in testis. The and subunits are expressed in a characteristic temporal and spatial pattern in sperm and precursor cells. In mature
sperm, the subunit is observed along the entire flagellum, whereas the short 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
Ca2+ indicator Fluo-3 shows that the CNG channels
serve as a Ca2+ entry pathway that responds more sensitively to cGMP than to cAMP. Assuming that CNG
channel subtypes differ in their Ca2+ permeability, dissimilar localization of and subunits may give rise to
a pattern of Ca2+ microdomains along the flagellum,
thereby providing the structural basis for control of
flagellar bending waves.
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