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The effect of triphenyllead chloride on membrane potential and electrical conductance of internodal cells of the alga Nitellopsis obtusa was studied. It was found that the compound studied, when present at 50 μM concentration, caused membrane depolarization and increased electrical conductance. The effect is, however, observed only after 0-30 min incubation, which may be due to the cumulation of triphenyllead in the cell wall before direct contact with the plasma membrane could occur. After 30 min incubation in triphenyllead solution the average relative changes in the membrane potential and electric conductance were -0.1±0.04 and 0.33±0.08 (n=12), respectively. These changes may be due to increased permeability of chloride ionsbrought about by the compound's interaction with channel proteins, or increased unspecific leakage of ions induced by a disturbance in the membrane structure.
Compression isotherms of mixed monomolecular layers at water-air interface, formed of lecithin (DPPC) and an organometallic compound (Me3PbCl, Me3SnCl, Et3PbCl, Et3SnCl) at various molar fractions (x = 0.0,0.2,0.4, 0.6, 0.8, 1.0) were studied. It was found that compression isotherms of the pure organometallic compounds (x = 1.0), in the range of mean molecular areas of 1.0 nm2 and ca. 0.15 nm2, did not show any practical increase in surface pressure. The isobaric relationship between mean molecular areas and molar fraction of an organometallic modifier are linear for most of the pressures chosen, which follows from analysis of the experimental isotherms obtained and demonstrates the ideal behaviour of the system under study. All the compounds studied form nearly ideally-behaving systems with lecithin. Presumably, the effects observed may be the result of molecular aggregation on the water phase surface, which in a mixed monolayer may lead to separation of the phases: organometallic compound - lecithin.
Patch-clamp technique was used to examine effect of trimethyllead chloride (Met3PbCl) on the SV channel activity in the red beet (Beta vulgaris L.) taproot vacuoles. It was found that in the control bath macroscopic currents showed typical slow activation and strong outward rectification of the steady-state currents. The addition of Met3PbCl to the bath solution blocked in a concentration-dependent manner SV currents in red beet vacuoles. The time constant, τ, increased several times in the presence of 100 μM trimethyllead chloride at all voltages tested. Trimethyllead chloride decreased significantly (by about one order of magnitude) the open probability of single channels. The recordings of single channel activity obtained in the presence and in the absence of Met3PbCl showed that organolead only slightly (by ca. 10%) decreased the unitary conductance of single channels. It was also found that Met3PbCl diminished significantly the number of SV channel openings, whereas it did not change the opening times of the channels. Within the present work the existence of spatial correlation beetwen ion channels of Beta vulgaris vacuolar membrane was shown. Moreover, the comparison of data collected in the control and in the presence of trimethyllead shows that organolead compound disturb not only the ion transport through the membrane, but also spacial correlations among channels. This work was supported by the KBN grant N305 336434
On the basis of Gortel & Grendel (J. Exp. Med., 1925, 41, 439-494) discovery, the importance of the lipid bilayer as an integral and indispensible component of the cell membrane is discussed. In particular, attention focuses on the interaction between membranes and amphiphilic substances. The effect on membranes of quaternary ammonium salts, both in the form of pesticides and oxidants as well as organic compounds of tin and lead are discussed in greater detail.
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