Analysis of the K+ Current Profile of Mature Rat Oligodendrocytes in situ

Abstract

Previous studies have reported that mature oligodendrocytes (OLGs) in vitro display various voltage-dependent K+ currents while in situ OLGs show only voltage-independent K+ currents. Given this discrepancy and the lack of information on myelinating OLG ion channel expression in situ, we characterized mature OLG currents in myelinating corpus callosum slices from 17 to 36-day old rats. OLGs were recorded in cell-attached and whole-cell patch-clamp configurations, displayed morphology typical of mature OLGs, and stained positive for myelin basic protein. OLGs displayed large voltage-independent currents that decayed during the voltage pulse and small voltage-activated outward currents. The latter were blocked by TEA, activated between -40 and -50 mV, and decayed slowly. The former were composed of large voltage-independent, time-dependent Ba2+ (1 mM)-sensitive currents, and voltage-dependent Cs+ (5 mM) and Ba2+ (100 mM)-sensitive currents that reversed near the K+ equilibrium potential and inactivated at hyperpolarized potentials, identifying them as inwardly rectifying K+ currents. Inwardly rectifying single-channel K+currents could be recorded in the cell-attached configuration. The estimated single-channel slope conductance was 30 pS. The steady-state open probability was voltage-dependent and declined from 0.9 to 0.5 between -80 and -150 mV. Overall, mature OLGs in situ possess time- and also voltage-dependent K+ currents, which may facilitate clearance of K+ released during axonal firing.

CB1 cannabinoid receptor‐dependent and ‐independent inhibition of depolarization‐induced calcium influx in oligodendrocytes

“…This result is consistent with the previously proposed idea that oligodendroglial Kir channels contribute to K 1 clearance during axonal firing (Berger et al, 1991;Butt and Kalsi, 2006;Chv atal et al, 1999;Gipson and Bordey, 2002;Zhou et al, 2007). Although the identity of the Kir channels involved in OL depolarization has not been established in the present study, previous data indicate that the Kir4.1 subunit might participate in this effect, consistent with the presence of Kir4.1 in rat optic nerve OL somata in situ as early as P5, with a subsequent marked increase at P10-15 (Kalsi et al, 2004).…”

“…The importance of OL function is highlighted by the clinical disability that characterizes demyelinating diseases such as multiple sclerosis. Beyond their role as insulators, OLs have been suggested to regulate function of axons, as they play important roles in the formation and maintenance of nodal regions in the buffering of extracellular K 1 during neuronal activity (Berger et al, 1991;Chv atal et al, 1999;Gipson and Bordey, 2002;Zhou et al, 2007). Conversely, axon-derived signals appear to modulate the proliferation of OL progenitors and their differentiation into myelinating cells (Barres and Raff, 1993;Colello et al, 1995;Demerens et al, 1996;Gallo et al, 1996;Ghiani et al, 1999;Neusch et al, 2001;Stevens et al, 2002).…”

Downregulation of Platelet-Derived Growth Factor-α Receptor-Mediated Tyrosine Kinase Activity as a Cellular Mechanism for K+-Channel Regulation during Oligodendrocyte DevelopmentIn Situ

“…Previous functional studies performed in situ have only examined K ϩ -channel expression at the two extremes of oligodendrocyte development, i.e., OPs and/or differentiated oligodendro-cytes, or have not accurately identified the lineage stage of the recorded cells (Berger et al, 1991;Chittajallu et al, 2002;Gipson and Bordey, 2002;Nashmi et al, 2002;Yuan et al, 2002). Therefore, relatively little is known about the time course of ion channel regulation with regard to intermediate lineage stages, such as those characterized by O4 expression.…”

Current ideas on central chemoreception by neurons and glial cells in the retrotrapezoid nucleus

“…Oligodendrocytes and polydendrocytes belong to the same lineage. Oligodendrocytes are myelin-producing cells usually identified by antibody labeling for myelin basic protein (17). Oligodendrocytes are also electrically distinct in that they have low membrane resistance, exhibit mostly voltage-independent K ϩ currents, and express glutamate transporters but not AMPA receptors (17).…”

“…Oligodendrocytes are myelin-producing cells usually identified by antibody labeling for myelin basic protein (17). Oligodendrocytes are also electrically distinct in that they have low membrane resistance, exhibit mostly voltage-independent K ϩ currents, and express glutamate transporters but not AMPA receptors (17). Polydendrocytes are glia progenitors present in all brain regions throughout life (45); they are identified immunohistochemically by expression of NG2 (45), an integral membrane chondroitin sulfate proteoglycan.…”