{'fraction_non_alphanumeric': 0.035583464154892726, 'fraction_numerical': 0.024594453165881738, 'mean_word_length': 4.494252873563219, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Heterogeneous distribution of fast and slow potassium channels in myelinated rat nerve fibres.

1. Potassium currents were measured in voltage‐clamped single myelinated rat nerve fibres before and after paranodal demyelination with 0.2% pronase or 0.2% lysolecithin added to the external solution. Sodium currents were blocked by 300 nM‐tetrodotoxin. For the purpose of comparison, intact frog nerve fibres were also investigated. 2. Our results suggest the existence of at least two distinct types of K+ channels in the intact node of Ranvier, one with slow and another with fast gating kinetics, in the ratio 4:1. 3. In the rat nodal membrane, slow K+ channels have voltage‐dependent time constants of K+ deactivation with tau n = 68 ms at E = ‐105 mV and tau n = 26 ms at E = ‐150 mV at 20 degrees C. The activation curve of the slow K+ conductance is sigmoid with an inflexion point at ‐60 mV. This means that about 35% of the slow K+ channels are in the open state at the resting potential of ‐77 mV. Slow K+ channels could be blocked by 10 mM‐tetraethylammonium chloride, but were insensitive to 4‐aminopyridine. 4. After paranodal demyelination the ratio of fast to slow K+ channels increased from 17 to 83%. As in the frog (Dubois, 1981 alpha), the population of fast K+ channels in the rat may consist of two different subgroups, both of which can be blocked by 4‐aminopyridine. 5. Demyelination was accompanied by an increase in the capacity current which was used to estimate the exposed membrane area. The density of slow and fast K+ channels was calculated from the quotient of the steady‐state K+ conductance to membrane area. The density of the slow K+ channels is maximal in the nodal membrane and decreases to 1/31 in the internode. By contrast, the distribution of the fast K+ channels differs, their density being maximal in the paranode and decreasing to one‐sixth in the node and internode.