Cytochalasin D attenuates the desensitisation of pressure-stimulated vesicle fusion in guard cell protoplasts

Fusion of vesicular membranes with the plasma membrane during pressure-driv en swelling of guard cell protoplasts was studied using patch clamp capacit ance measurements. Hydrostatic pressure pulses were applied via the patch p ipette and resulted in an immediate and linear increase in membrane capacit ance, a parameter proportional to the surface area. In any given protoplast , pressure-stimulated increases in membrane capacitance could be provoked r epetitively. However, the rate of rise in capacitance upon the same strengt h of stimulation decreased exponentially with time (tau = 4 min) for subseq uent pressure stimuli. This process was the result of a desensitisation of the plasma membrane to mechanical forces. Incubation of guard cell protopla sts in cytochalasin D, which depolymerises actin filaments, nearly abolishe d this desensitisation process. These results suggest that membrane stretch initiates a reactive process that may fortify or stabilise the plasma memb rane of guard cell protoplasts.