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Chronic hypoxia up‐regulates α 1H T‐type channels and low‐threshold catecholamine secretion in rat chromaffin cells
Author(s) -
Carabelli V.,
Marcantoni A.,
Comunanza V.,
De Luca A.,
Díaz J.,
Borges R.,
Carbone E.
Publication year - 2007
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2007.132274
Subject(s) - exocytosis , depolarization , hyperpolarization (physics) , medicine , endocrinology , chemistry , hypoxia (environmental) , chromaffin cell , catecholamine , extracellular , membrane potential , biophysics , stimulation , patch clamp , electrophysiology , secretion , biology , adrenal medulla , biochemistry , oxygen , organic chemistry , nuclear magnetic resonance spectroscopy
α 1H T‐type channels recruited by β 1 ‐adrenergic stimulation in rat chromaffin cells (RCCs) are coupled to fast exocytosis with the same Ca 2+ dependence of high‐threshold Ca 2+ channels. Here we show that RCCs exposed to chronic hypoxia (CH) for 12–18 h in 3% O 2 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 Ca 2+ channels already available at −50 mV with the same gating, pharmacological and molecular features as the α 1H isoform. Chronic hypoxia had no effects on cell size and high‐threshold Ca 2+ 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 Ca 2+ . 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 μ m Ni 2+ 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 μ m Ni 2+ . 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.