Submitted on July 24, 2006
Accepted on February 21, 2007
Mitochondrial Ca2+-activated K+ channels are more efficient at reducing mitochondrial Ca2+ overload in rat ventricular myocytes
Sung Hyun Kang1, Won Sun Park2, Nari Kim2, Jae Boum Youm2, Mohamad Warda1, Jae Hong Ko2, Eun A Ko3, and Jin Han2*
1 Mitochondrial Signaling Laboratory, Department of Physiology and Biophysics, College of Medicine, Biohealth Products Research Center, Cardiovascular and Metabolic Disease Research Center, Inje University, Busan, Korea, Republic of
2 Mitochondrial Signaling Laboratory, Department of Physiology and Biophysics, College of Medicine, Biohealth Products Research Center, Cardiovascular and Metabolic Disease Research Center, Inje University, Busan, Korea, Republic of; Busan, Korea, Republic of
3 Department of Medicine, University of California, San Diego, California, United States
* To whom correspondence should be addressed. E-mail: Phyhanj{at}inje.ac.kr.
We investigated the role of mitochondrial ATP-sensitive potassium (mitoKATP) channel , mitochondrial big conductance Ca2+-activated potassium (mitoBKCa) channel , and mitochondrial permeability transition pore (MPTP) in ouabain-induced increase of mitochondrial Ca2+ (mitoCa2+) in native rat ventricular myocytes by loading cells with rhod-2 AM. To overload mitoCa2+, cells were pretreated with ouabain before application of mitoKATP, mitoBKCa, and/or MPTP opener.
Application of 1 mM ouabain increased the rhod-2-sensitive fluorescence intensity (160±5.0 % of control), which was dramatically decreased to control level on application of diazoxide and NS 1619 in a dose-dependent manner (half-inhibition values of 78.3 µM and 7.78 µM in diazoxide and NS 1619, respectively). This effect was reversed by selective inhibition of mitoKATP channel by 5-HD, mitoBKCa channel by paxilline, and mitochondrial permeability transition pores (MPTPs) by cyclosporine A. Although application of diazoxide did not reduce mitoCa2+ during prolonged exposure to ouabain (long time exposure to ouabain), application of NS 1619 reduced mitoCa2+.
These results suggest that although both mitoBKCa and mitoKATP channels contribute to reducing ouabain-induced mitoCa2+ overload, activation of the mitoBKCa channel is more efficient at reducing ouabain-induced mitoCa2+ overload in our experimental model.
