Prion peptide fragment PrP[106-126] forms distinct cation channel types.

Abstract

Using the lipid bilayer technique we have optimized the recording conditions and confirmed that PrP[106-126] (KTNMKHMAGAAAAGAVVGGLG) forms single ion channels. Based on the conductance and kinetic parameters of the single channel currents recorded in 250/50 mM KCl cis/trans we have found that the PrP[106-126]-formed heterogeneous cation channels that differ in their conductance and kinetic properties. The most frequently observed PrP[106-126]-formed single cation channels were those of: (a) a GSSH- and TEA-sensitive channel with fast kinetics (n = 47). The current-voltage (I-V) relationship of this channel, that has a reversal potential E(rev) of -33 mV close to the equilibrium potential for K(+) (E(K) -35 mV), exhibited inward and outward rectification. The values of the maximal slope conductance (g(max)) were 138 and 141 pS at positive and negative potentials, respectively. The values of the permeability ratios were 1.0:0.87:0.72:0.49:0.41 for K(+) > Rb(+) > Na(+) > Cs(+) > Li(+) respectively. The probability of the channel being open (P(o)) and the frequency (F(o)) had bell-shaped curves with a peak at membrane potential (V(m)) between -10 and -5 mV whereas the mean open and closed times (T(o) and T(c)) had inverted bell-shaped curves; (b) a 4'-4'-dithiodipyridin (DTT)-sensitive channel with slow kinetics (n = 32). The I-V relationship of this channel that had an E(rev) of -35 mV and a g(max) of 41 pS at positive V(m) was non-linear. The parameter P(o) increased at positive V(m) to 0.6-0.7 at +80 mV. F(o) had an asymmetrical bell-shaped curve with a peak of 314 events/sec at -80 mV. The values of T(o) and T(c) were 312 and 164 msec at +120 mV, respectively; (c) a large channel (n = 24 channels) that had five equally spaced subconductances showed time-dependent fast and slow transitions at positive and negative V(m), respectively. The inactivation ratio I(ss)/I(i) was V(m) dependent and described by a bell-shape. The I-V relationship of this channel that had a E(rev) of -22 mV was non linear. The value of g(max) was 900 and 1444 pS at positive and negative V(m)s, respectively. The value of P(o) was 0.6 at negative V(m)s between -160 and -80 mV and 0.23 at +140 mV. F(o) increased from 22 events/sec at -160 mV to 80-100 events/sec at between +80 and +100 mV. T(o) decreased from 375 msec between -160 and -80 mV to 1-2 msec at V(m)s between 0 and +160 mV. In contrast, T(c) decreased from 160-240 msec at membrane voltages (V(m)s) between -160 and -80 mV. The biophysical properties of these channels indicate that they are capable of modifying cellular functions via modification of V(m) and electrolyte homeostasis of the cell.