The potassium channel opener NS1619 modulates calcium homeostasis in muscle cells by inhibiting SERCA.

NS1619 (1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazole-2-one) is widely used as a large-conductance Ca(2+)-activated K(+) (BKCa) channel opener. It was previously reported that activation of BKCa channels by NS1619 could protect the cardiac muscle against ischaemia and reperfusion injury. This study reports the effects of NS1619 on intracellular Ca(2+) homeostasis in H9C2 and C2C12 cells as well as its molecular mechanism of action. The effects of NS1619 on Ca(2+) homeostasis in C2C12 and H9C2 cells were assessed using the Fura-2 fluorescence method. Ca(2+) uptake by sarcoplasmic reticulum (SR) vesicles isolated from rat skeletal muscles and sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) activity were measured. The effect of NS1619 on the isometric force of papillary muscle contraction in the guinea pig heart was also examined. H9C2 and C2C12 cells treated with NS1619 released Ca(2+) from internal stores in a concentration-dependent manner. Ca(2+) accumulation by the SR vesicles was inhibited by NS1619 treatment. NS1619 also decreased the activity of SERCA derived from rat skeletal muscle. The calcium release from cell internal stores and inhibition of SERCA by NS1619 are pH dependent. Finally, NS1619 had a profound effect on the isometric force of papillary muscle contraction in the guinea pig heart. These results indicate that NS1619 is a potent modulator of the intracellular Ca(2+) concentration in H9C2 and C1C12 cells due to its interaction with SRs. The primary target of NS1619 is SERCA, which is located in SR vesicles. The effect of NS1619-mediated SERCA inhibition on cytoprotective processes should be considered.