The potassium channel opener CGS7184 activates Ca2+ release from the endoplasmic reticulum

Abstract

CGS7184 (ethyl 1-[[(4-chlorophenyl)amino]oxo]-2-hydroxy-6-trifluoromethyl-1H-indole-3-carboxylate) is a synthetic large-conductance Ca2+-activated potassium (BKCa) channel opener. The existing literature suggests that potassium channels are involved in cardioprotection, particularly during ischemia-reperfusion events. However, the cellular mechanisms mediating the effects of CGS7184 remain unclear. In the present study, we investigated the effect of the BKCa channel opener CGS7184 on Ca2+ homeostasis in H9C2 and C2C12 cell lines, Ca2+ uptake by isolated sarcoplasmic reticulum (SR) vesicles, SR Ca2+-ATPase (SERCA) activity, and single-channel properties of the ryanodine receptor calcium release channel (RYR2) when incorporated into a planar lipid bilayer. The effects of CGS7184 on calcium homeostasis in C2C12 and H9C2 cell lines were measured with a Fura-2 fluorescent indicator. The BKCa channel opener CGS7184, when added to the H9C2 and C2C12 cells, caused a concentration-dependent release of calcium from internal stores. Calcium accumulation by the SR vesicles isolated from cardiac and skeletal muscle was inhibited by CGS7184 with a half-maximal inhibition value of 0.45±0.04μM and 0.37±0.03μM, respectively. The results of the present study indicate that the BKCa channel opener CGS7184 modulates cytosolic Ca2+ concentration in H9C2 and C1C12 cells due to its interaction with the endoplasmic reticulum (ER). CGS7184 approximately doubled the opening probability of RYR2 channels; however, the compound seemed to most strongly affect channels with a higher control activity. These results strongly suggest that the BKCa channel opener CGS7184 affects intracellular calcium homeostasis by interacting with the sarcoplasmic reticulum RYR2 channels.