Putative small conductance Ca2+‐sensitive K+ channels isoforms and splice variants in mitochondria of guinea pig cardiac ventricular myocytes

Abstract

Small Ca2+‐sensitive K+ channels (SKCa) exist in many cell types including cardiac atrial and ventricular. There are 3 isoforms of SKCa, i.e. SKCa 1, 2, and 3. Activation of SKCa channels may protect against ischemia (I) and reperfusion (R) injury. Recently we found SKCa channels exist in the inner mitochondrial membrane (IMM) of guinea pig cardiac ventricular myocytes and that SKCa channel opening protects against cardiac IR injury. It is unknown which SKCa isoforms and splice variants are specific for cardiac cell IMM so we searched for the gene products that might confer their distinct structural and functional characteristics. SKCa is expressed in cardiac ventricular cells, so ventricular tissue devoid of endovascular cells were used to extract total RNA, which was then reverse transcribed to cDNA. The resulting cDNA was amplified with SKCa 1, 2 and 3 gene‐specific primers. Results showed that both SKCa 2 and 3 were amplified, which suggests both isoforms may be expressed in ventricular mitochondria. Gene and amino acid sequence alignments showed the amplified SKCa 3 to be SKCa 3.1, which lacks residues 478–499, present in SKCa 3.2. Similar to rat SKCa 3.1, guinea pig SKCa 3.1 displayed a conserved COOH‐terminal but did not have a poly‐Glu repeat region. Our results indicate that in ventricular cell IMM there may exist two SKCa isoforms and at least one SKCa 3 splice variant that can be functionally characterized. (NIH, VA)