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

Abstract

Pluteanu F, Cribbs LL. T-type calcium channels are regulated by hypoxia/reoxygenation in ventricular myocytes. Am J Physiol Heart Circ Physiol 297: H1304 -H1313, 2009. First published August 7, 2009 doi:10.1152/ajpheart.00528.2009.-Low-voltageactivated 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 2ϩ (Cav)3.1 and Cav3.2 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 Ϫ30 mV (the hallmark of this channel) based on the shift of the voltage dependence of activation to more depolarized values and downregulation of Ca v3.1 at the mRNA level. Upon reoxygenation, both Ca v3.1 mRNA levels and the voltage dependence of total T-type current are restored, although differently for activation and inactivation. Using Ni 2ϩ , we distinguished different effects of hypoxia/reoxygenation on the two current components. Long-term incubation in the presence of 100 M 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-1␣ is involved in Ca v3.1 downregulation. Our results demonstrate that Ca v3.1 and Cav3.2 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. low-voltage-activated calcium channel; oxidative stress; cardiomyocytes SINCE THE INITIAL BIOPHYSICAL (34) and molecular characterization (5, 27, 36) of low-voltage-activated T-type calcium currents in heart and neurons, these channels have been studied in various systems and pathological conditions. T-type currents are reexpressed in the adult hypertrophied ventricle and in postmyocardial infarction (18), in the monocrotaline model of pulmonary hypertension and heart failure (24, 44), and in vitro in adult ventricular myocytes exposed to 10% FBS (9) and endothelin-1 (19), relating the T-type current to the pathology rather than to normal physiological function of the myocytes. The mechanisms for regulation of the T-type channels are incompletely characterized, largely due to the lack of specific inhibitors and the presence of the more robust L-type and store-operated calcium channels, which make it difficult to isolate T-type Ca 2ϩ channel functions, such as secretion (29), excitation (52), or transcription regulation (4).

Transcriptional regulation of α1H T-type calcium channel under hypoxia

“…However, a recent study confirmed that, in rat neonatal ductus arteriosus, ␣ 1G mRNA and protein are not changed under hypoxia (1% O 2 ) but rather upregulated significantly under oxygenation (1). Consequently, these seemingly conflicting data support the idea that hypoxia differentially modulates T-type Ca 2ϩ channels depending on cells type as stated previously (31).…”

“…Similarly, when cardiac ventricular myocytes were subjected to hypoxia/reoxygenation, both ␣ 1G and ␣ 1H were shown to be differentially regulated, with a decrease in ␣ 1G mRNA and an increase in ␣ 1H mRNA (31). Additionally, the observation that ␣ 1H is upregulated under hypoxia is in agreement with the presence of several potential hypoxia-inducible factor (HIF) binding sites within the 5=-flanking region of the gene.…”

“…These data confirm previous reports of ␣ 1G insensitivity to hypoxia (6,10). In contrast, exposing neonatal rat ventricular myocytes to hypoxia resulted in an HIF-dependent decrease in ␣ 1G mRNA and upregulation of ␣ 1H mRNA (31). This discrepancy in ␣ 1G expression may be due to the hypoxia method used, its severity (3% vs. 1% O 2 ), in addition to the cell model used in the different studies.…”

Caveolin-3 Overexpression Attenuates Cardiac Hypertrophy via Inhibition of T-type Ca2+ Current Modulated by Protein Kinase Cα in Cardiomyocytes

“…ated cardiac hypertrophy, we used cultured NMVMs, which are known to endogenously express the I Ca, T (11,31,32). Cultured NMVMs were treated with Ang-II (10 mol/liter) or vehicle for 48 h, and I Ca, T was measured.…”

The activities of endothelial elastase and cathepsin G in rats at oxidative stress caused by heavy metals salts

“…It is known too, that CoCl 2 serves as hypoxia-dependent factor [7,26,27], and endothelial cells respond to hypoxia by decreasing the degradation of hypoxia-inducible factor 1α. The accumulation of last leads to increase transcription of numerous proteins involved in cell growth and survival [28], that may cause the increase of EEl activity, synthesized by endothelial cells.…”