Energy expenditure induced by changes in the ion homeostasis of wheat root cells

A relationship between energy exchange and ion transport is the basis for the functional response of cells to stress factors. The aim of the present work was to estimate the energy expenditure for response reactions and adaptation that are dependent on the permeability of the plasma membrane of the excised root cells. We studied the dynamics of changes in the (i) energy flow as measured by the oxygen uptake rate and the heat production rate, (ii) the electrical membrane potential (MP) and (iii) the loss of potassium ions of the cells on prolonged (5 h) treatment with membrane active compounds, namely the specific K+-ionophore valinomycin (Val) and chlorpromazine (CPZ), an antagonist of calmodulin but with a wide spectrum of other action. It was shown that the early (2 h) response of the cells exposed to these compounds was an increase in the loss of K+ ions and a decrease in the MP that were more pronounced in the presence of CPZ. The rates of oxygen uptake and heat production by the cells in the presence of Val increased with time and were coupled with the restoration of ion homeostasis as measured by the reduced loss of K+ ions. It is supposed that in the presence of Val the energy dependent recovery of ion homeostasis occurred through the compensatory activation of a plasma membrane H+-ATPase and the increase of K+/H+-exchange. Compared to Val, CPZ had larger effect on the alteration of the membrane characteristics and energy expenditure even during the relatively short time of treatment. It is supposed that this happened because CPZ damaged the membranes of the cells as a result of its partition with membrane lipids. Therefore, more energy is needed to restore the cellular homeostasis in the presence of CPZ compared to Val.