The sensitivity of cells to stress factors is associated with the function of electrogenic pumps and depends on their energy conditions. Regulation of cell metabolism and corresponding energy expense can be achieved by means of shifts in ion homeostasis via changes in the structural and functional properties of the plasma membrane. In the present work, we studied the changes in the rates of respiration and heat production along with the electrical membrane potential (MP) in cells of the excised roots of 5 day old wheat seedlings (Triticum aestivum L.) while the ion conductivity of their plasma membranes was modulated by 20 muM valinomycin (Val) and 100 muM chlorpromazine (CPZ). It is shown that both of these compounds induced an enhancement of potassium ion loss. CPZ also reduces both respiration intensity and heat production after 2 h of exposure. The enhancement of K+ loss caused by the specific K+ ionophore, Val, had no disorganizing effect on plasma membranes, and was compensated by an increase in ATPase activity on the plasma membrane. The essential rise of plasma membrane ion conductivity induced by CPZ, the compound with a pronounced membrane effect, was followed by a considerable inhibition of root respiration and heat production. These results point to the lack of cell energy resources to eliminate the damaging effect of CPZ. (C) 2004 Elsevier B.V. All rights reserved.