Single voltage‐dependent potassium channels in rat peripheral nerve membrane.

Abstract

SUMMARY1. Voltage-dependent potassium channels were investigated in rat axonal membrane by means of the patch-clamp recording technique. Three different types of channels (F, I and S) have been characterized on the basis of their single-channel conductance, activation, deactivation and inactivation properties.2. The fast (F) channels were activated smoothly at potentials (E) between -50 and 50 mV (E50 = 4-6 mV). They had a conductance of 55 pS for inward current and 30 pS for outward current in solutions containing 155 mm K+ (high K+) on both sides of the membrane at 21-23 'C. The F-channels demonstrated the fastest deactivation, within 1-2 ms, and inactivated in a few hundreds of milliseconds. The time constant of inactivation was 143 ms at E = +40 mV.3. The intermediate (I) channels activated steeply between E =-70 and -50 mV (E50 = -64-2 mv) and had a single-channel conductance of 33 pS for inward and 18 ps for outward currents. The I-channels deactivated with intermediate kinetics with the time constants of 20-4 ms and 10-1 ms at E = -80 mV and E = -100 mV, respectively. Complete inactivation of the channels developed over tens of seconds. The time constant of inactivation was 7-4 s at E = + 40 mV.4. The slow (S) channels were active at potentials positive to -90 mV. Their conductance was 10 pS for inward currents. The time constant of activation of the S-channels was strongly potential dependent. At a holding potential of -100 mV the channels deactivated during a long time interval between 30 ms and 1 s, producing long-lasting tail currents. The mean time constant of deactivation for S-channels was 129 ms.5. The conductances of F-and I-channels measured under normal physiological conditions (Ringer solution in bath) were 17 and 10 pS, respectively. 6. Tetraethylammonium (TEA), the classic blocker of potassium channels, suppressed F-, I-and

Effects of K+ Channel Blockers on Developing Rat Myelinated CNS Axons: Identification of Four Types of K+Channels

“…In conclusion, the data obtained in the present study show that there exists three populations of 4-AP-sensitive channels in the rat optic nerve: a population of paranodal channels sensitive only to DTX-I that may correspond to the I-type (Kf 1 ) channels present in peripheral nerves (Corrette et al 1991;Safronov et al 1993); a population of nodal and paranodal/ internodal channels insensitive to DTX-I that may correspond to the F-type (Kf 2 ) channels (Corrette et al 1991;Safronov et al 1993); and a population of paranodal channels sensitive to both KTX and DTX-I never described up to now. It was established here that the sequestration of all these channels and their time-evolving patterns of expression are closely correlated with the process of myelin formation and maturation.…”

“…We observed here that the disappearance of the effects of TEA coincided with the decrease in the duration of the CAPs and in the length of their refractory period and that TEA increased the duration of the CAPs of 4-AP-treated nerves. These results suggested that TEA-sensitive channels have a slow activation rate like the S-type channels present in the peripheral nerves (Corrette et al 1991;Safronov et al 1993). TEA has also little effect on immature (3 wk old), mature (17 wk old), and demyelinated peripheral nerves (Eng et al 1988;Rasband et al 1998).…”

Association and Colocalization of the Kvβ1 and Kvβ2 β-Subunits with Kv1 α-Subunits in Mammalian Brain K+Channel Complexes

“…Using a similar logic, channels composed of Kv1.1, Kv1.2, and Kv␤ 2, such as those seen in juxtaparanodal regions and in basket cell terminals would be predicted to form DTX-sensitive, noninactivating, delayed rectifier channels, giving rise to I K(DTX) currents similar to those that have been described in peripheral neurons (Stansfeld and Feltz, 1988;Safronov et al, 1993). These DTX-sensitive, noninactivating and slowly inactivating currents at peripheral nodes of Ranvier have been studied extensively; however, such currents in central neurons are less well characterized, perhaps attributable to their inaccessibility at nodes and at presynaptic terminals.…”

Stochastic Population Model for Electrical Stimulation of the Auditory Nerve

“…We allowed the density of K s channels to vary from a floor value of 30 chan/µm 2 to 110 chan/µm 2 reported by [37, pg. 330] [41], and as a result of optimisation, found the values converge to 41.2e6 chan/mm 2 . Given the lack of gating kinetics data for I-and F-fast potassium channels, we amalgamated these currents into one fast-acting potassium channel K f , as has been done in [46].…”

“…Potassium current was modeled as two separate components -a fast one, K f , intended to represent intermediate and fast K + channels' current (I-and F-channels in [41]), and a slow component, K s . Rapidly activating and transient, K f current was included in our model to shorten the relative refractory period.…”