TY - JOUR
T1 - Chronic hypoxia up-regulates α1H T-type channels and low-threshold catecholamine secretion in rat chromaffin cells
AU - Carabelli, V.
AU - Marcantoni, A.
AU - Comunanza, V.
AU - De Luca, A.
AU - Díaz, J.
AU - Borges, R.
AU - Carbone, Emilio
PY - 2007/10/1
Y1 - 2007/10/1
N2 - α1H T-type channels recruited by β1- adrenergic stimulation in rat chromaffin cells (RCCs) are coupled to fast exocytosis with the same Ca2+ dependence of high-threshold Ca2+ channels. Here we show that RCCs exposed to chronic hypoxia (CH) for 12-18 h in 3% O2 express comparable densities of functional T-type channels that depolarize the resting cells and contribute to low-voltage exocytosis. Following chronic hypoxia, most RCCs exhibited T-type Ca2+ channels already available at -50 mV with the same gating, pharmacological and molecular features as the α1H isoform. Chronic hypoxia had no effects on cell size and high-threshold Ca2+ current density and was mimicked by overnight incubation with the iron-chelating agent desferrioxamine (DFX), suggesting the involvement of hypoxia-inducible factors (HIFs). T-type channel recruitment occurred independently of PKA activation and the presence of extracellular Ca2+. Hypoxia-recruited T-type channels were partially open at rest (T-type 'window-current') and contributed to raising the resting potential to more positive values. Their block by 50 μm Ni2+ caused a 5-8 mV hyperpolarization. The secretory response associated with T-type channels could be detected following mild cell depolarizations, either by capacitance increases induced by step depolarizations or by amperometric current spikes induced by increased [KCl]. In the latter case, exocytotic bursts could be evoked even with 2-4 m m KCl and spike frequency was drastically reduced by 50 μm Ni2+. Chronic hypoxia did not alter the shape of spikes, suggesting that hypoxia-recruited T-type channels increase the number of secreted vesicles at low voltages, without altering the mechanism of catecholamine release and the quantal content of released molecules.
AB - α1H T-type channels recruited by β1- adrenergic stimulation in rat chromaffin cells (RCCs) are coupled to fast exocytosis with the same Ca2+ dependence of high-threshold Ca2+ channels. Here we show that RCCs exposed to chronic hypoxia (CH) for 12-18 h in 3% O2 express comparable densities of functional T-type channels that depolarize the resting cells and contribute to low-voltage exocytosis. Following chronic hypoxia, most RCCs exhibited T-type Ca2+ channels already available at -50 mV with the same gating, pharmacological and molecular features as the α1H isoform. Chronic hypoxia had no effects on cell size and high-threshold Ca2+ current density and was mimicked by overnight incubation with the iron-chelating agent desferrioxamine (DFX), suggesting the involvement of hypoxia-inducible factors (HIFs). T-type channel recruitment occurred independently of PKA activation and the presence of extracellular Ca2+. Hypoxia-recruited T-type channels were partially open at rest (T-type 'window-current') and contributed to raising the resting potential to more positive values. Their block by 50 μm Ni2+ caused a 5-8 mV hyperpolarization. The secretory response associated with T-type channels could be detected following mild cell depolarizations, either by capacitance increases induced by step depolarizations or by amperometric current spikes induced by increased [KCl]. In the latter case, exocytotic bursts could be evoked even with 2-4 m m KCl and spike frequency was drastically reduced by 50 μm Ni2+. Chronic hypoxia did not alter the shape of spikes, suggesting that hypoxia-recruited T-type channels increase the number of secreted vesicles at low voltages, without altering the mechanism of catecholamine release and the quantal content of released molecules.
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U2 - 10.1113/jphysiol.2007.132274
DO - 10.1113/jphysiol.2007.132274
M3 - Article
C2 - 17690152
AN - SCOPUS:34848903331
VL - 584
SP - 149
EP - 165
JO - Journal of Physiology
JF - Journal of Physiology
SN - 0022-3751
IS - 1
ER -