Ion channels in rat microglia and their different sensitivity to lipopolysaccharide and interferon-gamma.
In order to study the voltage-dependent ion channels in microglia, and their possible modulation by pro-inflammatory substances like lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) 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 Vrev 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-dependent 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-gamma (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-gamma 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-gamma share some electrophysiological effects, but differ in others.
Visentin
S
S
Laboratory of Pathophysiology, Istituto Superiore di Sanitá, Rome, Italy.
Agresti
C
C
Patrizio
M
M
Levi
G
G
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002478:Cells, Cultured / Q000737:chemistry; D002586:Cesium / Q000494:pharmacology; D018118:Chloride Channels / Q000502:physiology; D007150:Immunohistochemistry; D007371:Interferon-gamma / Q000494:pharmacology*; D007473:Ion Channels / Q000502:physiology*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D017628:Microglia / Q000737:chemistry / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology; D011522:Protons; D051381:Rats; D012680:Sensitivity and Specificity; D013997:Time Factors
D018118:Chloride Channels; D007473:Ion Channels; D008070:Lipopolysaccharides; D015221:Potassium Channels; D011522:Protons; D002586:Cesium; D007371:Interferon-gamma