Responses of single mechanoreceptor crayfish neurons to weak extremely low frequency magnetic fields were studied over a wide range of frequencies from 0.001 to 100 Hz, and magnetic fields from 1 to 400 pT. Observed shifts of neuron impulse activity were weak and variable. They were usually characterized by a slow increase or decrease of spike frequency developing during tens of minutes with markedly variable latencies. Frequency and amplitude "action spectra" were complex, nonlinear, and included several bands (frequency and amplitude "windows"). Neuron response probabilities (if response type and field amplitudes were excluded from consideration) were maximal at 0.001, 0.3, 3, and 60 Hz. They were also maximal at 5, 20, 50, and 300 FT if field frequencies were not taken into account. Minimal neuron response probabilities were observed at 0.03, 0.8-2, 11-15, and 100 Hz and 1,10,30, and 100pT, respectively. 267 Copyright 0 1997 by Marcel Dekker, h e .
Photodynamic effect of chiorin e6 on bioelectric activity of single crayfish stretch receptor neuron was studied. The stable background firing of this cell provides precise evaluation of initial membrane activity shifts, dynamics of bioelectric changes, and terminal events leading to the cell death. Spikes of isolated neuron were amplified, and their frequency was continuously recorded. After 1 hour of stable control work neurons were incubated 30 mm in saline with various chiorin e6 concentrations from 30 to 500 nM, and then irradiated by helium-neon laser (632.8 nm, 0.3 W/cm). Irradiation increased firing frequency and then induced abrupt irreversible cessation of spike generation. Rate of firing acceleration and neuron lifetime quadratically depended on the dye concentration, hence the excitation of two dye molecules is need for neuron response. These data show that bioelectric activity of single nerve cell is very sensitive to chlorin e6 photodynamic injury and that plasma membrane is the main target ofphotodynamic effect.
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