Voltage‐dependent potassium currents in cultured trout oligodendrocytes

Abstract

Ionic currents were recorded in cultured oligodendrocytes from the brain of trout using the whole-cell configuration of the patch-clamp technique. Outward currents were evoked at membrane potentials more positive than -40 mV, which could be separated into two components according to their kinetic parameters and their sensitivity to the holding potential: a fast inactivating current which was completely suppressed by 4-aminopyridine and reduced by tetraethylammonium and a slow steady-state conductance which was similarly sensitive to both potassium channel blockers. The current reversal potential was close to the potassium equilibrium potential. In contrast to mammalian oligodendrocytes but in similarity with cultured Schwann cells, trout oligodendrocytes did not exhibit any inwardly rectifying currents at hyperpolarized membrane potentials.

Glutamate‐activated ionic currents in cultured astrocytes from trout: Evidence for the occurrence of non‐N‐methyl‐D‐aspartate receptors

“…Hence it is not clear if glutamate receptors represent a specialized feature of mammalian astrocytes or if they also occur in glial cells of phylogenetically older vertebrate species including fishes. Therefore in the present study, we performed whole-cell patch-clamp recordings of glutamate-induced currents from cultured then characterized and identified astrocytes of trout CNS, after we had previously characterized voltage-sensitive ionic currents in glial cultures of this fish species (Glassmeier et al, 1992(Glassmeier et al, , 1994.…”

Developmental changes of potassium currents of embryonic leech ganglion cells in primary culture

“…Therefore, steadystate inactivation is not sufficient to characterize an A-current. While 4-AP is often more selective for fast potassium currents (Thompson, 1977), non-specific effects were shown (Eder et al, 1991;Glassmeier et al, 1992). In this study, only currents with steady-state inactivation and reduction by 4-AP were therefore supposed to be A-currents.…”

Molecular structure and expression of shaker type potassium channels in glial cells of trout CNS

“…According to functional expression studies in frog oocytes mammalian Kv1.2 is a delayed rectifier potassium channel (Stühmer et al, 1989). Hence, it is likely that tsha1 accounts for the noninactivating component of the potassium outward current measured in trout oligodendrocytes and their progenitor cells by patch clamp analysis (Glassmeier et al, 1992). The transient component of this current could either be due to the tsha2 subtype or it might be generated by the association with an auxilliary ␤-subunit, similar as it was shown for mammalian shaker-related potassium channels, which become endowed with inactivating A-type current properties after coexpression with Kv␤1.2 in frog oocytes (Rettig et al, 1994).…”

“…Astrocytes were strongly stained with anti-goldfish GFAP antibodies (Nona et al, 1989) and exhibited a morphological heterogeneity ranging from a flat polygonal structure to a spindle-shaped morphology. Regarding their antigenic phenotype and their electrophysiological features, the cells in these cultures have been previously characterized in detail Glassmeier et al, 1992Glassmeier et al, , 1994.…”

“…Although a number of functional roles have been proposed for these channels, ranging from a contribution to potassium ion homeostasis to the control of cell proliferation, the physiological significance of glial potassium channels is still poorly understood. Recent patch clamp studies performed with astrocytes and oligodendrocytes from the trout central nervous system (CNS) have revealed a striking phylogenetic conservation of ion channel properties between glial cells of mammals and fish (Glassmeier et al, 1992;Glassmeier and Jeserich, 1995), advocating for their basic physiological importance. Unfortunately very little is known about the molecular structure and biochemical composition (Chiu et al, 1994;Roy et al, 1996) of glial potassium channels in general, and no structural data are available about those in the CNS of fish.…”