Stretch activation of the Aplysia S-channel.

The S-channel, a receptor-mediated K+ channel of Aplysia sensory neurons which functions in neuromodulation, bears a strong resemblance to the ubiquitous stretch-activated channels of snail neurons. Snail neuron stretch channels are stretch sensitive only in the patch, not at the macroscopic level, a situation which leaves open the question of their physiological role. If S-channels resemble snail stretch channels because both belong to the same general class of channels, the S-channel, too, should display stretch sensitivity in the patch. We show, using single-channel recording, that the S-channel can be activated by stretch. Furthermore, we show that Aplysia neurons in general have stretch-activated K+ channels. We suggest that the stretch-sensitive K+ channels of molluscan neurons and other preparations (e.g., Drosophila muscle, snail heart) are S-like channels, i.e., receptor-mediated channels which adventitiously exhibit mechanosensitivity in the patch.