Effect of trimethyllead chloride on slowly activating (SV) channels in red beet (Beta vulgaris L.) taproots

The patch-clamp technique was used to examine the effect of trimethyllead chloride (Met₃PbCl) on SV channel activity in red beet (Beta vulgaris L.) taproot vacuoles. It was found that in the control bath the macroscopic currents showed the typical slow activation and a strong outward rectification of the steady-state currents. An 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. When single channel properties were analyzed, only little channel activity could be recorded in the presence of 100 μM Met₃PbCl. 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 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. Taken together, these results suggest that Met₃PbCl binding site is located outside the channel selectivity filter.