AJP - Cell Physiology, Vol 262, Issue 4 C870-C875, Copyright © 1992 by American Physiological Society
N-methyl-D-aspartate increases cytosolic Ca2+ via G proteins in cultured hippocampal neurons
K. Harada, T. Yoshimura, K. Nakajima, H. Ito, Y. Ebina and R. Shingai
Department of Neurosurgery, School of Medicine, Yamaguchi University, Ube, Japan.
The changes of the cytosolic Ca2+ concentrations ([Ca2+]i) induced by
N-methyl-D-aspartate (NMDA) in fura-2-loaded cultured hippocampal neurons
from rat embryos were investigated by the fast application method, using a
fine pipe under extracellular Mg(2+)-free conditions. In the presence of
Ca2+, NMDA, at concentrations in excess of 3 microM, induced a biphasic
increase of [Ca2+]i, which consisted of an initial increase with a second
rise that occurred after cessation of drug application. Under Ca(2+)-free
conditions, NMDA (greater than 100 microM) in the absence of glycine or
NMDA (greater than 50 microM) in the presence of glycine (greater than 10
microM) induced intracellular Ca2+ mobilization, which was blocked by 30
microM 2-amino-5-phosphonovaleric acid (APV) and reduced by
islet-activating protein. When the neurons were superfused with Ca(2+)-free
solution, the application of 3-10 microM NMDA, which had been dissolved in
Ca(2+)-containing solution, induced the second phase [Ca2+]i increase,
whereas application of kainate, quisqualate, or stimulation by 50 mM K+ did
not. Islet-activating protein,
1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), and
D-sphingosine reduced the second phase [Ca2+]i increase. These results
suggest that NMDA-induced intracellular Ca2+ mobilization is potentiated by
the initial entry of Ca2+ into the cells and is regulated in an
islet-activating protein-sensitive manner.
