Na(+)‐activated K+ channels localized in the nodal region of myelinated axons of Xenopus.

Abstract

1. A potassium channel activated by internal Na+ ions (K'. channel) was identified in peripheral myelinated axons of Xenopus laevis using the cell-attached and excised configurations of the patch clamp technique. 5. A comparison of the number of ]K' channels in nodal and paranodal patches from the same axon revealed that the channel density was about 10-fold higher at the node of Ranvier than at the paranode. Moreover, a correlation between the number of K+N channels and voltage-dependent Na+ channels in the same patches was found, suggesting co-localization of both channel types.6. As weakly potential-dependent ('leakage') channels, axonal K'. channels may be involved in setting the resting potential of vertebrate axons. Simulations of Na+ ion diffusion suggest two possible mechanisms of activation of KM channels: the local increase of Na+ concentration in a cluster of Na+ channels during a single action potential or the accumulation in the intracellular axonal compartment during a train of action potentials.

Information processing in the axon

“…In addition, large-conductance calcium-dependent potassium channels (BK, also called Maxi-K or Slo1 channels) are present in axons and presynaptic terminals [15][16][17][18][19] . Finally, large conductance sodium-dependent potassium channels (K Na , also called Slack channels or Slo2.2) are found in myelinated axons 20,21 . All of these potassium channels usually accelerate the repolarization of the action potential, but they might also prevent repetitive discharge and reduce the width of the action potential.…”

Kinetic properties of unitary Na+‐dependent K+ channels in inside‐out patches from isolated guinea‐pig ventricular myocytes.

“…The majority of openings within a burst were long so that the mean was 3-87 ms, while closings tended to be brief and as a result P. within a burst was high. The infrequent appearance of very prolonged periods without activity suggests that the bursts themselves may be collected into clusters (Gibb & Colquhoun, 1992 (Rodrigo & Chapman, 1990;Kameyama et al 1994;Koh et al 1994). (2) (McManus & Magleby, 1989 (Rothberg et al 1996).…”

“…The organization of KNa channels within the cardiac muscle cell membrane is not known but they occur in a small minority of patches. A close association with voltage-dependent Na+ channels as would seem to occur in nodal regions of myelinated nerves, where it is involved in the repolarization of the action potential (Koh, Jonas & Vogel, 1994), would offer little functional advantage to cardiac muscle where the action potential is long. However, a close spatial association between Na+ pump sites and KNa channels has been suggested by Luk & Carmeliet (1990) and would be consistent with the effects of R56865 noted above.…”

NAD+Activates KNaChannels in Dorsal Root Ganglion Neurons

“…In some neurons, these channels have been suggested to control the resting membrane potential (Haimann et al, 1992;Koh et al, 1994;Bischoff et al, 1998). Recent evidence indicates that in adult medium-sized dorsal root ganglion (DRG) neurons, a single Na ϩ -dependent action potential can elicit a K Na current, and K Na channels were suggested to regulate the depolarizing after potential (DAP) (Gao et al, 2008).…”