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

Potassium (K+) channels are present in both mammalian testis and spermatozo a. Immunofluorescent detection of sperm-bound biotinylated charybdotoxin, a n inhibitor of Ca2+-activated and of delayed rectifier K+ channels, indicat ed that these ion channels are uniformly distributed over the surface of bo th heads and tails of unfixed rat epididymal spermatozoa. Reverse transcrip tion-polymerase chain reaction (RT-PCR) analysis on rat testis RNA with PCR primers, based on known nucleotide sequences of different classes of K+ ch annels, amplified sequences homologous to delayed rectifier K+ channels, In -situ RT-PCR on rat testis sections showed that these K+ channel transcript s are present in the cytoplasm of primary spermatocytes and post-meiotic el ongating spermatids. Northern blot analysis of various rat tissues identifi ed multiple K+ channel transcripts, some of which were observed only in tes tis. 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 dela yed rectifier K+ channel, Kv1.3. A method for rapid amplification of cDNA e nds was employed to amplify the 5' sequences of the rat testis cDNA but a u nique sequence could not be obtained. DNA sequencer traces suggest that mul tiple related K+ channels which differed at their 5' ends were amplified in rat testis.