DELAYED ACTIVATION OF SINGLE MECHANOSENSITIVE CHANNELS IN LYMNAEA NEURONS

Some stretch-activated (SA) channels challenged with suction jumps exh ibit adaptation, a dynamic behavior that can be overlooked because of its mechanical fragility. In previous studies of neuronal SA K channel s, we detected no adaptation, but the protocols used were not designed to detect dynamics. Here, we reproduce the adaptation seen by others in Xenopus SA cationic (Cat) channels but show that, with the same pro tocol, no adaptation occurs with SA K channels. Instead, SA K channels exhibit a different dynamic behavior, delayed activation. Lymnaea SA K channels subjected to pressure jumps responded after a 1- to 4-s del ay with a gradual, rather than abrupt, onset of activation. The delay was pressure dependent and was longer for patches from older cultured neurons. Delayed responses were fragile Like SA Cat channel adaptation ; they disappeared with repeated stimuli. Cytochalasin D decreased the delay and increased the stretch activation of SA K channels. Unlike S A Cat channel adaptation, which occurs only at hyperpolarized potentia ls, SA K channel delay was not voltage dependent. The note that once S A Cat and SAK channels are ''stripped'' of their fragile (cytoskeleton -dependent?) dynamics, however, their gating behaviors show Little fun damental difference; both are stretch activatable and have a higher op en probability at depolarized potentials.