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Astrocytes regulate developmental changes in the chloride ion gradient of embryonic rat ventral spinal cord neurons in culture
Author(s) -
Li YongXin,
Schaffner Anne E.,
Walton Marc K.,
Barker Jeffery 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.1469-7793.1998.847bm.x
Subject(s) - depolarization , bicuculline , reversal potential , muscimol , chemistry , neuroscience , gabaergic , membrane potential , extracellular , biophysics , electrophysiology , chloride channel , patch clamp , gabaa receptor , picrotoxin , spinal cord , astrocyte , microbiology and biotechnology , biology , receptor , central nervous system , biochemistry , inhibitory postsynaptic potential
1 Embryonic rat ventral spinal cord neurons were dissociated at day 15 and grown on: (i) poly‐D‐lysine (PDL); (ii) a confluent monolayer of type I astrocytes; or (iii) PDL in astrocyte‐conditioned medium (ACM) to examine the influence of astroglia on the regulation of GABA A receptor/Cl − channel properties. 2 Potentiometric oxonol dye recordings of intact cells indicated that embryonic neurons were uniformly depolarized by muscimol. The depolarizing effects disappeared in cells dissociated during the early postnatal period and recovered in culture for 24 h. Similar recordings using the calcium‐imaging dye fura‐2 AM revealed that GABA or muscimol triggered a sustained rise in cytosolic Ca 2+ (Ca 2+ c ) in embryonic neurons that was dependent on extracellular Ca 2+ , blocked by bicuculline and nifedipine and sensitive to changes in extracellular chloride. The incidence and amplitude of the Ca 2+ response decreased with time in vitro and was accelerated in neurons cultured on astrocytes compared with those on PDL. 3 Perforated patch‐clamp recordings revealed that GABA depolarized neurons in a Cl − ‐dependent and bicuculline‐sensitive manner. Both the resting membrane potential and the GABA equilibrium potential became more hyperpolarized with time in vitro.4 Astrocytes and ACM accelerated the transformation of GABAergic potential responses from depolarizing to hyperpolarizing. The change occurred over the first 4 days in co‐culture or in ACM but took more than 2 weeks in neurons cultured on PDL alone. 5 The intrinsic, elementary properties of GABA A receptor/Cl − channels including open time and unitary conductance changed independently of the presence of astrocytes or ACM. Mean open time of the dominant kinetic component decreased and conductance increased with time in vitro.6 In sum, astrocytes accelerate the developmental change in the Cl − ion gradient extrinsic to GABA A receptor/Cl − channels, which is critical for triggering Ca 2+ entry, without influencing parallel changes in the intrinsic properties of the channels.