Oxygen-sensing mechanisms are present in the chromaffin cells of the sheep adrenal medulla before birth

J Physiol. 1998 Jun 15;509 ( Pt 3)(Pt 3):887-93. doi: 10.1111/j.1469-7793.1998.887bm.x.


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 PO2 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 IA-type current. The delayed current had two components, a TEA-sensitive, Ca2+-dependent current and a component with the kinetic behaviour of a delayed rectifier. 4. Both types of current were oxygen sensitive. The IA-type current was reduced by 27.4 +/- 3.2 % when the PO2 was reduced to about 15 mmHg. With the delayed current, hypoxia reduced the amplitude by 26.9 +/- 2.4 %, largely by reduction of the Ca2+-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 Ca2+ channels, influx of Ca2+ and the subsequent secretion of catecholamines.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenal Glands / cytology
  • Adrenal Medulla / chemistry
  • Adrenal Medulla / cytology
  • Adrenal Medulla / physiology*
  • Animals
  • Calcium Channels / physiology
  • Calcium Channels, L-Type
  • Carotid Body / physiology
  • Cell Hypoxia / physiology
  • Cells, Cultured
  • Chemoreceptor Cells / physiology*
  • Chromaffin Cells / chemistry
  • Chromaffin Cells / physiology*
  • Female
  • Fetus / physiology*
  • Oxygen / metabolism*
  • Patch-Clamp Techniques
  • Potassium Channels / physiology
  • Pregnancy
  • Receptors, Cholinergic / physiology
  • Sheep


  • Calcium Channels
  • Calcium Channels, L-Type
  • Potassium Channels
  • Receptors, Cholinergic
  • Oxygen