A Xanthine-Derivative K(+)-Channel Opener Protects against Serotonin-Induced Cardiomyocyte Hypertrophy via the Modulation of Protein Kinases

This study investigated whether KMUP-1, a xanthine-derivative K(+) channel opener, could prevent serotonin-induced hypertrophy in H9c2 cardiomyocytes via L-type Ca(2+) channels (LTCCs). Rat heart-derived H9c2 cells were incubated with serotonin (10 μM) for 4 days. The cell size increased by 155.5%, and this was reversed by KMUP-1 (≥1 μM), and attenuated by the LTCC blocker verapamil (1 μM) and the 5-HT(2A) antagonist ketanserin (0.1 μM), but unaffected by the 5-HT(2B) antagonist SB206553. A perforated whole-cell patch-clamp technique was used to investigate Ca(2+) currents through LTCCs in serotonin-induced H9c2 hypertrophy, in which cell capacitance and current density were increased. The LTCC current (I(Ca,L)) increased ~2.9-fold in serotonin-elicited H9c2 hypertrophy, which was attenuated by verapamil and ketanserin, but not affected by SB206553 (0.1 μM). Serotonin-increased I(Ca,L) was reduced by KMUP-1, PKA and PKC inhibitors (H-89, 1 μM and chelerythrine, 1 μM) while the current was enhanced by the PKC activator PMA, (1 μM) but not the PKA activator 8-Br-cAMP (100 μM), and was abolished by KMUP-1. In contrast, serotonin-increased I(Ca,L) was blunted by the PKG activator 8-Br-cGMP (100 μM), but unaffected by the PKG inhibitor KT5823 (1 μM). Notably, KMUP-1 blocked serotonin-increased I(Ca,L) but this was partially reversed by KT5823. In conclusion, serotonin-increased I(Ca,L) could be due to activated 5-HT(2A) receptor-mediated PKA and PKC cascades, and/or indirect interaction with PKG. KMUP-1 prevents serotonin-induced H9c2 cardiomyocyte hypertrophy, which can be attributed to its PKA and PKC inhibition, and/or PKG stimulation.