T-type calcium channels are regulated by hypoxia/reoxygenation in ventricular myocytes

Low-voltage-activated calcium channels are reexpressed in ventricular myocytes in pathological conditions associated with hypoxic episodes, but a direct relation between oxidative stress and T-type channel function and regulation in cardiomyocytes has not been established. We aimed to investigate low-voltage-activated channel regulation under oxidative stress in neonatal rat ventricular myocytes. RT-PCR measurements of voltage-gated Ca(2+) (Ca(v))3.1 and Ca(v)3.2 mRNA levels in oxidative stress were compared with whole cell patch-clamp recordings of T-type calcium current. The results indicate that hypoxia reduces T-type current density at -30 mV (the hallmark of this channel) based on the shift of the voltage dependence of activation to more depolarized values and downregulation of Ca(v)3.1 at the mRNA level. Upon reoxygenation, both Ca(v)3.1 mRNA levels and the voltage dependence of total T-type current are restored, although differently for activation and inactivation. Using Ni(2+), we distinguished different effects of hypoxia/reoxygenation on the two current components. Long-term incubation in the presence of 100 microM CoCl(2) reproduced the effects of hypoxia on T-type current activation and inactivation, indicating that the chemically induced oxidative state is sufficient to alter T-type calcium current activity, and that hypoxia-inducible factor-1alpha is involved in Ca(v)3.1 downregulation. Our results demonstrate that Ca(v)3.1 and Ca(v)3.2 T-type calcium channels are differentially regulated by hypoxia/reoxygenation injury, and, therefore, they may serve different functions in the myocyte in response to hypoxic injury.