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.