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Oxygen‐sensing mechanisms are present in the chromaffin cells of the sheep adrenal medulla before birth
Author(s) -
Rychkov G. Y.,
Adams M. B.,
McMillen I. C.,
Roberts M. L.
Publication year - 1998
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 - 10.1111/j.1469-7793.1998.887bm.x
Subject(s) - adrenal medulla , chromaffin cell , carotid body , endocrinology , medicine , patch clamp , biophysics , hypoxia (environmental) , chemistry , oxygen , adrenal gland , chemoreceptor , electrophysiology , biology , catecholamine , receptor , organic chemistry
1 The ability of the fetal adrenal medulla to respond directly to hypoxaemia and secrete catecholamines before the development of a functional innervation of the gland is essential for intrauterine survival. The cellular mechanisms involved in this response to low P O2 are not known, although the presence of oxygen‐sensitive K + channels in carotid body chemoreceptor cells and other sites suggests that these might underlie the chromaffin cell response. 2 Whole‐cell patch‐clamp techniques have been used to study K + currents during normoxia and hypoxia in chromaffin cells isolated from the adrenal glands of fetal sheep. 3 Two types of chromaffin cells were observed, those with a fast inactivating K + current and a larger capacitance and those with a delayed K + current and smaller capacitance. No cell showed both types of current. The fast inactivating current showed voltage‐dependent inactivation and was blocked by 1 mM 4‐aminopyridine, characteristics of an I A ‐type current. The delayed current had two components, a TEA‐sensitive, Ca 2+ ‐dependent current and a component with the kinetic behaviour of a delayed rectifier. 4 Both types of current were oxygen sensitive. The I A ‐type current was reduced by 27.4 ± 3.2 % when the P O2 was reduced to about 15 mmHg. With the delayed current, hypoxia reduced the amplitude by 26.9 ± 2.4 %, largely by reduction of the Ca 2+ ‐dependent component. 5 In the presence of hypoxia, reduction in the amplitude of these oxygen‐sensitive K + currents would increase the frequency and duration of action potentials, leading to increased activation of the L‐type Ca 2+ channels, influx of Ca 2+ and the subsequent secretion of catecholamines.