Cholesterol-Independent Effects of Methyl-β-Cyclodextrin on Chemical Synapses
Figure 4
MβCD alters postsynaptic responsiveness.
Intracellular voltage recordings were made from L1 muscle fibers within segment IV while iontophoretically applying L-glutamate and simultaneously injecting hyperpolarizing current intracellularly. These recordings detected changes in input resistance of muscle fibers as well as any changes in postsynaptic receptor sensitivity. Under no conditions was there an effect on the input resistance of muscle fibers (open and closed squares). A. Cold-acclimatized group (open symbols). Responsiveness to iontophoretically applied glutamate (open circles) revealed a significant (P<0.05) transient increase following the application of 10 mM MβCD, that subsequently resulted in a 17%/min reduction in the sensitivity to applied glutamate which plateaued within 6 min. Attempts to recover responsiveness, using a cholesterol-loaded cyclodextrin (Ch-HPβCD) and a saline wash, were unsuccessful. B. Warm-acclimatized group (closed symbols). While there was no immediate change in responsiveness to applied glutamate (closed circles), a subsequent gradual reduction during exposure to MβCD occurred. Application of Ch-HPβCD recovered responsiveness to 90% of initial values, and a subsequent saline wash resulted in a return to control values. C-D. Control recordings from cold- and warm-acclimatized groups were stable throughout the 40min recording period. Insets: recordings of input resistance and responsiveness to iontophoretically applied glutamate at selected time points. * indicates P<0.05, † indicates P<0.01. N = 7. Scale bars: 15 mV, 250 ms.