Poster: Membrane transport

Abs # 181: Modulatory effects of various metal ions on the activity of 450 pS channel prepared from tomato roots

Presenter:	Kim, Young-Kee , Kim6@wisc.edu
Authors	Kim, Young-Kee  (A) (B)  Shin, Dae-Seop  (B)
Affiliations:	(A): University of Wisconsin (B): Chungbuk National University, KOREA

In order to characterize ion channels present in tomato roots, microsomes were incorporated into an artificial lipid bilayer arranged for electrophysiological analysis. Of the five different ion channels that could be distinguished from the currents recorded under voltage clamp conditions, a 450 pS conductance was found most frequently. This channel displayed subconductance states of 450, 257 and 105 pS. All subconductance states showed linear current - voltage relationships. At positive holding potentials, high frequency of transient channel openings was observed; however, at negative potentials, the open times were long and open probability high. Po was 0.83 at -40 mV. When an additional 50 mM K⁺ or Na⁺ was added to the cis side of bilayer, the reversal potentials shifted in the negative direction to near -10 mV. Thus, the 450 pS cation channel selects poorly between K⁺ and Na⁺. In the presence of 100 μ metal ions, the channel activity was severely inhibited by La³⁺, Ba²⁺, and Zn²⁺, and Po was decreased to 0.2 or even less. However, Al³⁺ and Cd²⁺ decreased the activity by only 20%. Interestingly, each metal ion showed different kinetics of channel inhibition. While 500 μ La³⁺ inhibited the activities of all subconductance state, 1 mM Zn²⁺ inhibited all except the 105 pS state. Cd²⁺ changed the gating of the channel from a long-opening state to brief transient openings even at negative holding potentials. These data represent that the metal ions may have different binding sites on the channel protein and could be useful modulators to investigate structural characteristics as well as the functional roles of the 450 pS channel on the root physiology.