Ion channels of the tonoplast membrane of Nitella hookeri

Ion channels in cytoplasmic droplets of the characean algae Nitella hooketi have been studied using the patch clamp technique. This technique enables the measurement of the ionic current through single membrane channels. Several channels have previously been identified and characterised in characean tonoplast membranes. These include at least one type of potassium channel (in Chara australis; Lühring, 1986, C. gymtlophylla; Andjus et aI., 1999 and Djurisic & Andjus, 2000, and C. corallina; Tyerman & Findlay, 1989) and one chloride channel (in C. coraiiilla; Tyerman & Findlay, 1989). The tonoplast membrane of N. hooken was surveyed for its similarity to those in previous studies. A potassium channel was observed that correlated with reports of either a 60pS channel (Tyerman & Findlay, 1989), or a 170pS channel that showed a predominant subconductance state that had a conductance of 60pS (Luhring, 1999). Other potassium channels observed conducted at ~40pS, ~20pS, and ~80pS. A chloride channel was recorded that resembled that reported in the tonoplast membrane of C. Coralline (21pS). Other Chloride channels observed conducted at ~78pS, and ~100pS. A channel protein's reaction to glycation, via the Maillard reaction, was studied using the improved patch clamp technique. Preliminary results show that methylglyoxal (a glycating agent) addition decreases channel conductance while a control of time (no addition) showed no similar reduction. It is hypothesised that cross-linking and other covalent modification, known to result from the Maillard reaction, has altered the channel's structure to induce this change. A similar experiment using glutaraldehyde (another glycating agent known to react at a greater speed) gave similar preliminary results