Characterization of a high-conductance, voltage-dependent cation channel from the plasma membrane of rye roots in planar lipid bilayers

✍ Scribed by Philip J. White

• Publisher: Springer-Verlag
• Year: 1993
• Tongue: English
• Weight: 985 KB
• Volume: 191
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00195756

✦ Synopsis

Plasma-membrane vesicles were purified by aqueous-polymer two-phase partitioning of a microsomal membrane fraction from rye (Secale cereale L.) roots and incorporated into planar 1-palmitoyl-2-oleoyl phosphatidylethanolamine bilayers. A high-conductance cation channel (a maxi cation channel) was characterized from single-channel electrical recordings. The channel was incorporated into the bilayer with its cytoplasmic surface facing the trans compartment and voltages were referenced cis with respect to trans. The channel was permeable to both monovalent and divalent cations. The unitary conductance was 451 pS in symmetrical 100 mM KC1 and 213 pS in symmetrical 100 mM BaC12. The permeability ratio PK:PBa was 1.00:2.56. Unitary conductances declined in the order K + > Rb + > Cs + > Na + > Li + (monovalent cations) and Ba2+>Sr2+>Ca2+> Mg 2+ >Co 2+ > Mn 2+ (divalent cations). The relative permeabilities of monovalent cations mirrored their conductivity sequence, whereas the permeabilities of all divalent cations were similar. The maxi cation channel showed complex kinetics, exhibiting both voltage-and time-dependent inactivation and voltage-dependent gating. The voltage dependence of the kinetics shifted in parallel with changes in the reversal potential of the channel. In symmetrical 100mM KC1, following a voltage step from zero to the test voltage, the channel inactivated and the active-channel lifetime (ri) shortened exponentially as the test voltage was increased. The channel always opened immediately upon depolarization to zero volts, indicating that inactivation of the channel did