Molecular characterization of a voltage-gated potassium channel expressed in rat testis

Potassium (K+) channels are present in both mammalian testis and spermatozoa. Immunofluorescent detection of sperm-bound biotinylated charybdotoxin, an inhibitor of Ca2+-activated and of delayed rectifier K+ channels, indicated that these ion channels are uniformly distributed over the surface of both heads and tails of unfixed rat epididymal spermatozoa. Reverse transcription-polymerase chain reaction (RT-PCR) analysis on rat testis RNA with PCR primers, based on known nucleotide sequences of different classes of K+ channels, amplified sequences homologous to delayed rectifier K+ channels, In-situ RT-PCR on rat testis sections showed that these K+ channel transcripts are present in the cytoplasm of primary spermatocytes and post-meiotic elongating spermatids. Northern blot analysis of various rat tissues identified multiple K+ channel transcripts, some of which were observed only in testis. An attempt to obtain a full length rat testis K+ channel cDNA sequence gave an assembled sequence of 2693 base pairs with >90% homology to a delayed rectifier K+ channel, Kv1.3. A method for rapid amplification of cDNA ends was employed to amplify the 5' sequences of the rat testis cDNA but a unique sequence could not be obtained. DNA sequencer traces suggest that multiple related K+ channels which differed at their 5' ends were amplified in rat testis.