Electrophysiological Changes That Accompany Reactive GliosisIn Vitro

Abstract

An in vitro injury model was used to examine the electrophysiological changes that accompany reactive gliosis. Mechanical scarring of confluent spinal cord astrocytes led to a threefold increase in the proliferation of scar-associated astrocytes, as judged by bromodeoxyuridine (BrdU) labeling. Whole-cell patch-clamp recordings demonstrated that current profiles differed absolutely between nonproliferating (BrdU Ϫ ) and proliferating (BrdU ϩ ) astrocytes. The predominant current type expressed in BrdU Ϫ cells was an inwardly rectifying K ϩ current (K IR ; 1.3 pS/pF). BrdU Ϫ cells also expressed transient outward K ϩ currents, accounting for less than one-third of total K ϩ conductance (G). In contrast, proliferating BrdU ϩ astrocytes exhibited a dramatic, approximately threefold reduction in K IR (0.45 pS/pF) but showed a twofold increase in the conductance of both transient (K A ) (0.67-1.32 pS/pF) and sustained (K D ) (0.42-1.10 pS/pF) outwardly rectifying K ϩ currents, with a G KIR : G KD ratio of 0.4. Relative expression of G KIR :G KD led to more negative resting potentials in nonproliferating (Ϫ60 mV) versus proliferating astrocytes (Ϫ53 mV; p ϭ 0.015). Although 45% of the nonproliferating astrocytes expressed Na ϩ currents (0.47 pS/pF), the majority of proliferating cells expressed prominent Na ϩ currents (0.94 pS/pF). Injury-induced electrophysiological changes are rapid and transient, appearing within 4 hr postinjury and, with the exception of K IR , returning to control conductances within 24 hr. These differences between proliferating and nonproliferating astrocytes are reminiscent of electrophysiological changes observed during gliogenesis, suggesting that astrocytes undergoing secondary, injury-induced proliferation recapitulate the properties of immature glial cells. The switch in predominance from K IR to K D appears to be essential for proliferation and scar repair, because both processes were inhibited by blockade of K D .

Modulation of Kv1.5 Currents by Src Tyrosine Phosphorylation: Potential Role in the Differentiation of Astrocytes

“…Current subtraction shows that the PP2-sensitive current is an outwardly rectifying potassium current (Fig. 6 B), reminiscent of the sustained delayed rectifier current previously characterized in these cells (MacFarlane and Sontheimer, 1997) and similar to the current carried by Kv1.5 (Roy et al, 1996).…”

“…Thus, these channels are integral in regulating membrane potential in both excitable and unexcitable cells. Membrane potential has long been implicated in the regulation of cell cycle progression (Cone, 1970), and delayed rectifier channels, in particular, have been implicated both directly (Knutson et al, 1997;MacFarlane and Sontheimer, 1997;Ghiani et al, 1999) and indirectly (Chiu and Wilson, 1989;Puro et al, 1989;Pappas et al, 1994;Gallo et al, 1996;Pappas and Ritchie, 1998) in glial cell proliferation. Thus, although the specific mechanisms by which potassium channel activity is regulated during proliferation require further investigation, we suggest that the activity of Src family protein tyrosine kinases may play a role in regulating proliferation-dependent channel activity in astrocytes.…”

Prostaglandin E2 and 4‐Aminopyridine Prevent the Lipopolysaccharide‐Induced Outwardly Rectifying Potassium Current and Interleukin‐1β Production in Cultured Rat Microglia

“…The presence of this K+ OR is a robust indicator of the functional state of the cell (Fischer et al, 1995). It is possible that the expression of this outward current is necessary for the activation of microglia, as has been observed in astrocytes (MacFarlane and Sontheimer, 1997). It may also promote the survival of microglia in an activated state.…”

Mislocalization of Kir channels in malignant glia

“…Cells were cultured in Dulbecco's modified Eagle medium/F12 (DMEM/F12) (Gibco, Grand Island, NY) supplemented with 7% fetal calf serum (FCS) (Hyclone, Logan, UT) and 2 mM glutamine (Gibco). Primary cultures of spinal cord or cortical astrocytes were obtained by slightly modified methods described previously (MacFarlane and Sontheimer, 1997). Briefly, the spinal cord or cortex was dissected into icecold serum-free EMEM (Gibco) plus 20 mM glucose, meninges were stripped, and tissue was minced and placed into an O 2 -saturated papain solution (Worthington, Lakewood, NJ)) for 20 min.…”