Characterization of a voltage-dependent cation-channel from the plasma membrane of rye (Secale cerealeL.) roots in planar lipid bilayers

✍ Scribed by Philip J. White

• Publisher: Springer-Verlag
• Year: 1994
• Tongue: English
• Weight: 765 KB
• Volume: 193
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00192529

✦ 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 voltage-dependent cation-channel became incorporated into the bilayer with its cytoplasmic surface facing the trans compartment (which was grounded) and was characterized from single-channel recordings. The channel had a unitary conductance of 174 pS in symmetrical 100 mM KC1. The selectivity towards monovalent cations, determined from both conductance measurements in symmetrical 100 mM cation chloride and from permeability ratios in the presence of (cis: trans) 100 mM cation chloride: 100 mM KC1, was Cs > K > Rb > Na. The channel was also permeable to both Ba 2+ and Ca 2+. Although the unitary conductances in symmetrical 100 mM BaC12 and CaC12 were only 46 pS and 40 pS, respectively, the apparent permeabilities of the divalent cations relative to K + were greater than expected (PK:PBa:Pca, 1.00: 1.66:2.60). This anomaly might result from competition between divalent and monovalent cations for an intrapore binding site. The channel exhibited complex gating kinetics, which were modulated in response to changes in the zero-current (reversal) potential of the channel (Erev). In symmetrical 100 mM KC1 the channel inactivated at positive voltages greater than 100 mV and the activated channel exhibited a high probability of being in an open-state (Po > 0.90) at all voltages between + 100 mV. Channel P0 approximated unity at voltages in the range -60 to + 20 mV. As more-negative voltages were applied, P0 decreased gradually. In contrast, as more positive voltages