The nature of subthreshold changes in excitable plasma membranes has been investigated in stem parenchyma cells of Cucurbita pepo L. during action-potential generation induced by gradual cooling (from 23 to 10 ° C). The character of the subthreshold depolarization of excitable cells is shown to be mainly defined by a decrease in the activity of the plasma-membrane electrogenie pump (H(+)-ATPase). In its turn, the pump activity is controlled by thermal changes in the structure of the membrane lipid matrix. Based on the results obtained, a sequence of subthreshold changes has been suggested in which thermally induced structural rearrangements of membrane lipids play the role of trigger.

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