The effects of over-expression of the FK506-binding protein FKBP12.6 on K+ currents in adult rabbit ventricular myocytes

This study examines the effects of the intracellular protein FKBP12.6 on action potential and associated K+ currents in isolated adult rabbit ventricular cardiomyocytes. FKBP12.6 was over-expressed by similar to 6 times using a recombinant adenovirus coding for human FKBP12.6. This over-expression caused prolongation of action potential duration (APD) by similar to 30%. The amplitude of the transient outward current (I (to)) was unchanged, but rate of inactivation at potentials positive to +40 mV was increased. FKBP12.6 over-expression decreased the amplitude of the inward rectifier current (I (K1)) by similar to 25% in the voltage range -70 to -30 mV, an effect prevented by FK506 or lowering intracellular [Ca2+] below 1 nM. Over-expression of an FKBP12.6 mutant, which cannot bind calcineurin, prolonged APD and affected I (to) and I (K1) in a similar manner to wild-type protein. These data suggest that FKBP12.6 can modulate APD via changes in I (K1) independently of calcineurin binding, suggesting that FKBP12.6 may affect APD by direct interaction with I (K1).