The physiology of locust auditory receptors
- Cite this article as:
- Hill, K.G. J. Comp. Physiol. (1983) 152: 475. doi:10.1007/BF00606437
Intracellular recordings from locust auditory receptors reveal discrete, subthreshold depolarizations of the cell membrane, with variable amplitude up to about 5 mV, that are the first electrical sign of mechanosensory transduction (Fig. 1).
Hyperpolarization of the receptor cell membrane causes an increase in the amplitude of the discrete depolarizations without suppressing their occurrence (Fig. 2).
In the absence of acoustic stimuli, the subthreshold potentials appear to occur spontaneously at random. The mean frequency of the recorded potentials varies widely between cells (Figs. 1, 2, 3).
The potentials also occur in response to sound stimuli. The probability of a response following a brief tone increases from near zero to 1.0 with increasing intensity of the tone (Fig. 4). The number of potentials occurring during an extended tone initially increases as the stimulus intensity is increased (Fig. 5) and typically, the discrete potentials superimpose to form a graded receptor potential (Fig. 6), as occurs in visual receptor cells.
In both a train of discrete potentials and a sustained depolarization, the amplitude may progressively decline from its initial peak, indicative of adaptation.
Receptor potentials produced by weak stimulation are characteristically noisy. Amplitude and frequency analyses of the membrane voltage noise recorded during sound stimulation suggests that the noise results from the superposition of discrete depolarizations, consistent with direct observations.
The first electrical sign of transduction in locust auditory receptors is a quantal membrane voltage response. By analogy with vision, it is suggested that discrete mechano-chemical events may lead to activation of ionic conductance channels in receptor cell membranes, possibly via an intermediate biochemical process.