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A characterization of muscarinic receptor‐mediated intracellular Ca 2+ mobilization in cultured rat hippocampal neurones
Author(s) -
Irving Andrew J.,
Collingridge Graham 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.1469-7793.1998.747bg.x
Subject(s) - carbachol , muscarinic acetylcholine receptor , thapsigargin , extracellular , endocrinology , medicine , depolarization , chemistry , hippocampal formation , muscarinic acetylcholine receptor m1 , biophysics , receptor , biology , biochemistry
1 The properties of muscarinic receptor‐mediated Ca 2+ mobilization were investigated in hippocampal cultures using fluorescent imaging techniques. 2 Somatic responses to carbachol (1‐10 μ m ) were observed in 21 % of neurones under control conditions (5.4 mM K + , 1.8 mM Ca 2+ , 0.5‐1 μ m tetrodotoxin). Smaller responses were observed in Ca 2+ ‐free medium. 3 In cells where responses to carbachol were absent under control conditions, responses were often observed following depolarization with high extracellular K + (16.2‐25 mM). These responses decreased in magnitude with time after the depolarizing episode. Mobilization of Ca 2+ from stores using caffeine (50 mM) exhibited similar properties. 4 Carbachol responses were greatly facilitated in the presence of moderate elevations in extracellular K + or Ca 2+ levels (2‐ or 3‐fold, respectively). These conditions were usually, but not always, associated with a small increase in cytosolic Ca 2+ levels (< 50 nM). 5 Muscarinic responses in 10.8 mM K + were inhibited by 80–95 % in the presence of the L‐type voltage‐gated Ca 2+ channel antagonists nitrendipine (2‐5 μ m ) or nifedipine (10 μ m ). Depletion of intracellular Ca 2+ stores with thapsigargin (2‐10 μ m ) blocked responses. 6 Oscillatory Ca 2+ mobilizing responses were observed in some cells. Their expression was facilitated by moderate cytosolic Ca 2+ elevations and by increasing the duration of carbachol exposure. 7 Ca 2+ mobilizing responses were also observed in dendritic regions. These were smaller than somatic responses, but had faster decay kinetics. 8 In conclusion, muscarinic receptor‐mediated Ca 2+ mobilization in cultured hippocampal neurones shows a strong Ca 2+ dependence. Moderate intracellular Ca 2+ rises greatly facilitate muscarinic responses and uncover, in some cells, oscillatory Ca 2+ mobilization. These effects appear to reflect the loading state of intracellular Ca 2+ stores.