Single K⁺ channel properties in cultured mouse Schwann cells: Conductance and kinetics

Abstract

Cultured Schwann cells are characterized by a strong outward rectification of the membrane; the threshold of the outward currents is close to the resting membrane potential of about -50 mV (Gray et al.: In Ritchie, Keynes (eds): Ion Channels in Neural Membranes. New York: Alan R. Liss, Inc., pp 145-157, 1986). These outward currents show up a heterogeneity among the cultured Schwann cells: some cells displayed inactivating, others non-inactivating outward currents (Hoppe et al.: Pflügers Arch 415:22-28, 1989). In this study we characterized the single channel currents using the patch-clamp technique in the intact patch recording configuration. The conductance of all recorded channels was 10-12 pS (5.6 mM [K+]o). These channels were K+ selective since changes in extracellular [K+] resulted in changes of the reversal potential as predicted for an exclusively K+ selective pore. The reversal potentials also predicted an intracellular [K+] of 60 mM indicating that the K+ equilibrium potential is slightly negative to the membrane potential. Analysis of the kinetic behavior of the channels resolved two different types of behaviour: 40% inactivated during a depolarizing voltage step, the others showing no sign of inactivation. The analysis of open probability and gating properties in the steady state showed up more differences between these two channel types: mean open probability peaked at about 10 mV for inactivating channels, while it continuously increased for non-inactivating channels. The inactivation time constants of averaged single channel and whole cell currents were similar and showed both a similar voltage dependency. We conclude that cultured Schwann cells express either two types of K+ channels with similar conductance or a channel which can acquire two functional states and that these channels can account for the different types of K+ currents observed in these cells.

Tyrosine Phosphatases ε and α Perform Specific and Overlapping Functions in Regulation of Voltage-gated Potassium Channels in Schwann Cells

“…Single-channel currents could be detected easily at potentials 20 mV more positive than the resting membrane potential, i.e., above Ϫ30 mV, with current amplitudes increasing with further depolarization ( Figure 4A). The unitary current-voltage relations indicated a mean single-channel conductance of 10 pS for the four mouse genotypes ( Figure 4B; our unpublished data), a value very close to that obtained previously in Schwann cells from normal NMRI mice (Verkhratsky et al, 1991).…”

Determination of the membrane potential of cultured mammalian schwann cells and its sensitivity to potassium using a thiocarbocyanine fluorescent dye

“…The membrane potential values obtained from these experiments rely on the determination of [K+Ii. Most of the data originate from patch clamp experiments, range from 55 to 89 mM, and may contain errors caused by internal dialysis of the cell by the patch pipette (Shrager et al, 1985;Verkhratsky et al, 1991). The absolute potential values obtained from the different calibration procedures are in good agreement with each other (Table 1) and are within the range reported, anecdotally, in patch clamp studies of approximately -40 mV (Gray et al, 1984).…”

Two types of 4‐aminopyridine‐sensitive potassium current in rabbit Schwann cells.

“…For example, Konishi (1989) has recorded outward K+ currents in mouse cultured Schwann cells that showed similarities with type I currents including rapid activation and steep voltage dependence. But, in these mouse cells, a 1 s prepulse to -35 mV produced 50 % inactivation at 22-24°C (see also : Verkhratsky, Hoppe & Kettenmann, 1991;Amedee, Ellie, Dupouy & Vincent, 1991).…”