Sl. Mironov et Dw. Richter, Hypoxic modulation of L-type Ca2+ channels in inspiratory brainstem neurones: Intracellular signalling pathways and metabotropic glutamate receptors, BRAIN RES, 869(1-2), 2000, pp. 166-177
Brief hypoxia (2 min) enhances the activity of L-type Ca2+ (Ca-L) channels.
The effect is dye to glutamate release and concomitant stimulation of meta
botropic glutamate receptors of the mGLUR1/5 type [22] [S.L. Mironov, D.W.
Richter, L-type Ca2+ channels in inspiratory neurones and their modulation
by hypoxia, J. Physiol. 512 (1998) 75-87.]. Besides increasing single chann
el activity, hypoxia induces a negative shift of the activation curve and s
lows down the inactivation of the Ca-L current. In the present study we inv
estigated these effects further, aiming to reveal intracellular signalling
pathways that mediate the coupling between mGLURs and Ca-L channels. Channe
l activity was recorded in cell-attached patches from inspiratory brainstem
neurones of neonatal mice (PG-ll). Ca-L channels were inhibited by the mGl
uR2/3 agonists. mGluR1/5 agonists accelerated and mGluR2/3 agonists suppres
sed the respiratory output, and correspondingly modified the hypoxic respon
se of the respiratory center. Ca-L channels were also modulated by protein
kinase C-L but this did not prevent the hypoxic modification of channel act
ivity. G-protein activators enhanced and G-protein inhibitors suppressed th
e Ca-L channel activity, and in the presence of these agents the effects of
hypoxia were abolished. Ryanodine but not thapsigargin inhibited the chann
el activity and occluded the hypoxic potentiation. Only G-protein-specific
agents and ryanodine prevented the slowing down of inactivation induced by
hypoxia. Our data indicate that coupling between mGluR1/5 and Ca-L channels
is mediated by pathways that utilize G-proteins and ryanodine receptors. G
lutamate release and concomitant activation of Ca-L channels are responsibl
e for accelerating of respiratory rhythm during early hypoxia. (C) 2000 Els
evier Science B.V. All rights reserved.