Abstract:Interrelations between the action of acetylcholine (ACh) and cadmium ions (Cd 2+ ) on bioelectrogenesis of Nitellopsis obtusa cells were investigated. We analyzed repetitively triggered action potentials (AP), their reproducibility, shape and dynamics of membrane potential after AP induction. ACh significantly increased membrane permeability only at high concentrations (1 mM and 5 mM). Repolarisation level of action potential after the first stimulus was much more positive in all cells treated with ACh as compared to the control. Differences of membrane potentials between points just before the first and the second stimuli were 23.4±.0 mV (control); 40.4±5.9 mV (1 mM ACh solution) and 57.7 ± 8.5 mV (5 mM ACh solution). Cd 2+ at 20 μM concentration was examined as a possible inhibitor of acetylcholinesterase (AChE) in vivo. We found that cadmium strengthens depolarizing effect of acetylcholine after the first stimulus. The highest velocity of AP repolarization was reduced after ACh application and Cd 2+ strengthened this effect. There were no differences in dynamics of membrane potential after repetitively triggered action potentials in ACh or ACh and Cd 2+ solutions. This shows that cadmium in small concentration acts as inhibitor of acetylcholinesterase.

A biotesting method for the assessment of acute sublethal toxicity to charophyte cells of Nitellopsis obtusa was developed and applied for the study of Vilnius and Visaginas wastewaters (WW). This computer-assisted testing procedure was based on the recording of the electrophysiological response of up to 16 single algal cells simultaneously. Membrane parameters of living cells were measured according to the K+-anaesthesia method modified for multichannel recording with extracellular electrodes. Concentration-dependent monotonical decrease of cell resting potential, induced by toxic WW action, was used to determine an effective concentration (EC) values. A multistep time-saving procedure, when the cell group was exposed to subsequent treatment with increasing WW concentrations (30 min per treatment), proved to be adequate for biotesting. The ECs obtained by this procedure were in good agreement with those obtained alternatively by undertaking onestep testing (i.e., 60 min exposure per concentration per cell group). The relative sensitivity of the cellular electrophysiological response, as a toxicity end point, was confirmed by comparing it with lethal concentration (LC) responses in 96-and 192-h exposure tests conducted on the same N. obtusa cells. For Vilnius WW samples taken on different dates, the EC5, s ranged from 27 to 46% WW and corresponded to 96-h LC5, s of 28-50% WW. In contrast, Visaginas WWs sampled before and after chlorination showed no toxic effect either at the membrane or whole cell level. 0 7995 by John Wiley & Sons, Inc.of the food web and contributors of oxygen in the aquatic ecosystem, are scarcely employed in biotesting. It is clear, however, that some species of charophytes, for example, could certainly satisfy the requirements characterizing microbiotesting (Blake, 1991).Stoneworts are widely distributed, abundantly grow in the ground plantations of clean fresh or brackish waters (Minkevieius and Trainauskaite, 1957), and are sensitive to pollution. The giant charophyte cell separated from talloma and kept in artificial pond water can be considered to be a single organism that maintains

The role of acetylcholine (ACh) as a signalling molecule in plants was investigated using a model system of Characeae cells. The effect of ACh on conductance of K+ channels in Nitella flexilis cells and on the action potential generation in Nitellopsis obtusa cells after H+-ATPase inhibition, where repolarization occurs after the opening of outward rectifying K+ channels, was investigated. Voltage-clamp method based on only one electrode impalement was used to evaluate the activity of separate potassium ion transport system at rest. We found that ACh at high concentrations (1 mM and 5 mM) activates K+ channels as the main membrane transport system at the resting state involved in electrogenesis of Characeaen membrane potential. We observed that ACh caused an increase in duration of AP repolarization of cells in K+ state when plasmalemma electrical characteristics are determined by large conductance K+ channels irrespective of whether AP were spontaneous or electrically evoked. These results indicate interference of ACh with electrical cellular signalling pathway in plants.

Aluminium induced membrane potential (E m ) changes and potential changes during repolarization phase of the action potential (AP) in the internodal cells of Nitellopsis obtusa after blocking H + -ATPase activity by DCCD were investigated. Micromolar concentrations of DCCD are sufficient togive complete and irreversible inhibition of proton pumping. The membrane potential was measured by conventional glass-microelectrode technique. We found that the half-amplitude pulse duration differs significantly between standard conditions, after DCCD application, and after H + -ATPase blocking and subsequent Al 3+ treatment: 4.9, 7.7 and 17.2 seconds, respectively. We propose that in the short term (2 hours) treatment of Al 3+ , the decrease in membrane potential was compensated for by H + -ATPase activity. Blocking H + -ATPase activity by DCCD can enhance the influence of Al 3+ on the bioelectrical activity of cell membranes.

Biology has moved from a bench-based discipline to a bioinformational science in modern times but application of computational and analytical methods of informatics in it is still a problem for many researchers and students of biology. We suggest to integrate cost effective and practical combination of the real and the virtual laboratories into the undergraduate biological science curriculum. This laboratory work illustrates passive and active electrical properties of plant cell membranes while introducing basic principles of electrophysiological recording, data acquisition and analysis. As the object for investigation in this laboratory work large cells of starry stonewort (Nitellopsis obtusa) were used. The simple program for experiment control and express visualization of recorded data was developed. Experiment proposed in this paper is easy implemented with a minimum of laboratory equipment, materials and gives an experience of computerized biological experiment.

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Objectives: Our living environment is composed of mixed pollution.

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