Effects of Nitric Oxide on Voltage-Gated K⁺ Currents in Human Cardiac Fibroblasts through the Protein Kinase G and Protein Kinase A Pathways but Not through S-Nitrosylation

This study investigated the expression of voltage-gated K⁺ (K ) channels in human cardiac fibroblasts (HCFs), and the effect of nitric oxide (NO) on the K currents, and the underlying phosphorylation mechanisms. In reverse transcription polymerase chain reaction, two types of K channels were detected in HCFs: delayed rectifier K⁺ channel and transient outward K⁺ channel. In whole-cell patch-clamp technique, delayed rectifier K⁺ current (I ) exhibited fast activation and slow inactivation, while transient outward K⁺ current (I ) showed fast activation and inactivation kinetics. Both currents were blocked by 4-aminopyridine. An NO donor, -nitroso- -acetylpenicillamine (SNAP), increased the amplitude of I in a concentration-dependent manner with an EC value of 26.4 µM, but did not affect I . The stimulating effect of SNAP on I was blocked by pretreatment with 1H-(1,2,4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or by KT5823. 8-bromo-cyclic GMP stimulated the I . The stimulating effect of SNAP on I was also blocked by pretreatment with KT5720 or by SQ22536. Forskolin and 8-bromo-cyclic AMP each stimulated I . On the other hand, the stimulating effect of SNAP on I was not blocked by pretreatment of -ethylmaleimide or by DL-dithiothreitol. Our data suggest that NO enhances I , but not I , among K currents of HCFs, and the stimulating effect of NO on I is through the PKG and PKA pathways, not through -nitrosylation.