Stretch-activated cation channels of leech neurons exhibit two activity modes

Single-channel recordings were used to characterize two activity modes of stretch activated channels (SACs) in identified neurons of the leech. Clear-cut differences in the activity pattern of SACs from freshly desheathed cell bodies and from cultured AP cells were observed. SACs of inside-out patches, made by 'gentle' sealing and excised from cell bodies of freshly desheathed ganglia exhibited spike-like (SL) activity, with a mean channel open time (MCOT) shorter than 10 ms. Fitting of dwell open-time distributions revealed time constants shorter than 2 and 10 ms. This activity was characterized by a chord conductance of about 115 pS. SACs from cultured cells often displayed activity just after excision. MCOT exceeded 200 ms and the time constants of open-time interval distributions were longer than 10 and 100 ms. Furthermore, this activity pattern was characterized by both sub- (about 80 and 40 pS) and super-conductance (150 pS) levels, hence denoted as multiconductance (MC) mode. The percentage of open time spent at the main subconductance level (80 pS) was significantly higher in patches isolated from growth cones than in those from cell bodies of cultured neurons. The two activity modes (SL and MC) should belong to the same channel because both modes have a common main conductance value and exhibit outward rectification, stretch sensitivity and blockage by Gd3+ and gentamicin. Cytochalasin D applied to the cytoplasmic side induced activation of SACs or increased their ongoing activity. Thus, the observed differences in the expression of the two activity modes of SACs might be associated with different arrangements of the cortical cytoskeleton.