Receptor potentials and action potentials in Drosera tentacles

Voltage fluctuations identified as receptor potentials can be detected with electrodes applied to the mucilage surrounding the head of a tentacle of Drosera intermedia if the head is stimulated by contact with a live insect, by the touch of a clean, inert object, or by application of salt solutions. Associated with a low receptor potential are action potentials, which occur at a frequency dependent on the magnitude of the receptor potential. These action potentials can be detected with electrodes applied to any region of the stalk of the tentacle. Inflection of the lower stalk follows the occurrence of action potentials. Inflection is minute for isolated action potentials but large and rapid when several occur within a brief interval. The apparent amplitude of action potentials recorded from the stalk is independent of receptor potential amplitude, but that of action potentials recorded from the mucilage commonly decreases as the receptor potential deviates from the baseline and increases as it returns. It is suggested that variation of apparent amplitude of the action potentials may result from postulated variation in the resistance of receptor membranes.