FMRFAMIDE AND MEMBRANE STRETCH AS ACTIVATORS OF THE APLYSIA S-CHANNEL

The long-standing distinction between channels and transporters is bec oming blurred, with one pump protein even able to convert reversibly t o a channel in response to osmotic shock. In this light, it is plausib le that stretch channels, membrane proteins whose physiological roles have been elusive, may be transporters exhibiting channel-like propert ies in response to mechanical stress. We recently described a case, ho wever, where this seems an unlikely explanation. An Aplysia K channel whose physiological pedigree is well established (it is an excitabilit y-modulating conductance mechanism) was found able to be activated by stretch. Here we establish more firmly the identity of this Aplysia co nductance, the S-channel, as a stretch channel. We show that the perme ation and fast kinetic properties of the stretch-activated channel and of the FMRF-amide-activated S-channel are indistinguishable. We have also made progress in extending the kinetic analysis of the stretch ch annel to situations of multiple channel activity. This analysis implem ents a novel renewal theory approach and is therefore explained in som e detail.