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Ion channels in rat microglia and their different sensitivity to lipopolysaccharide and interferon‐γ
Author(s) -
Visentin S.,
Agresti C.,
Patrizio M.,
Levi G.
Publication year - 1995
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490420402
Subject(s) - tetraethylammonium , ion channel , conductance , patch clamp , microglia , biophysics , chemistry , lipopolysaccharide , reversal potential , channel blocker , electrophysiology , extracellular , medicine , biochemistry , biology , inflammation , receptor , potassium , physics , calcium , organic chemistry , condensed matter physics
In order to study the voltage‐dependent ion channels in microglia, and their possible modulation by proinflammatory substances like lipopolysaccharide (LPS) and interferon‐γ (IFN‐γ) we employed the patch‐clamp technique on purified rat microglial cell subcultures grown for 1–5 days in control condition or after a 24 hour treatment with those agents. Regardless of the culture condition, almost 100% of the cells presented inward‐rectifying (IR) K + currents identified by the following features: (a) extracellular K + ‐dependence of V rev and whole‐cell conductance; (b) inward‐rectifying property; (c) channel blocking mechanism by Cs + ; and (d) single channel conductance of 27 pS. A ‘n’ type outward‐rectifying (OR) K + current was present in 30% of the cells during the first 2 days of subcultivation. Its occurrence was strongly dependent on the preparation, varying from 0% to almost 80%, and it decreased to 13% of the cells after three days in culture. It showed the following features: (i) threshold of activation close to ‐30 mV; (ii) sigmoid current onset; (iii) voltage‐% kinetics; and (iv) sensitivity to 4‐aminopyridine (4‐AP) and tetraethylammonium (TEA). Furthermore, we detected two ion currents not previously described in microglia: (i) a slowly activating outward current which appeared at potentials more positive than +20 mV and with a reversal potential close to 0 mV, tentatively identified as a proton current; and (ii) a Cl − conductance identified in ion substitution experiments as the current sensitive to the Cl − channel blocker SITS. The two agents, LPS (20–2,000 ng/ml) and IFN‐γ (10–100 u/ml), shared the following effects: (a) enhancement of membrane capacitance, and (b) increase of OR current amplitude and frequency of occurrence. Moreover, IFN‐γ was also able to increase IR current density, especially in cells with ameboid morphology, while LPS was ineffective. We conclude that the voltage‐dependent ion channel pattern of microglia is more complex than previously thought and that activating agents such as LPS and IFN‐y share some electrophysiological effects, but differ in others. © 1995 Wiley‐Liss, Inc.