ClC-3-independent Sensitivity of Apoptosis to Cl– Channel Blockers in Mouse Cardiomyocytes

It has been shown that Cl–/HCO3– exchangers and Cl– channels, both of which are sensitive to stilbene derivatives, have essential roles in the mechanism of apoptosis induction. Staurosporine-induced apoptosis in neonatal mouse cardiomyocytes was prevented by a stilbene derivative, DIDS. To clarify whether Cl–/HCO3– exchangers or Cl– channels are targets of DIDS and whether ClC-3 is involved in the apoptotic process, staurosporine-induced reduction of cell viability, DNA laddering and caspase-3 activation were examined in cultured mouse ventricular myocytes derived from wild-type and ClC-3-deficient mice. Staurosporine-induced apoptosis and its DIDS sensitivity in ambient HCO3–-free conditions in which operation of Cl–/HCO3– exchangers is minimized were indistinguishable from when HCO3– was present. Apoptosis was also prevented by application of a non-stilbene-derivative Cl– channel blocker, NPPB, which cannot block Cl–/HCO3– exchangers. Cardiomyocytes derived from ClC-3-deficient mice similarly underwent apoptosis after exposure to staurosporine; moreover, apoptosis was prevented by application of DIDS or NPPB. Thus, we conclude that in cardiomyocytes, apoptosis is critically dependent on operation not of Cl–/HCO3– exchangers but of Cl– channels which are distinct from ClC-3.