BAND-PASS FILTERING BY VOLTAGE-DEPENDENT MEMBRANE IN AN INSECT PHOTORECEPTOR

The membrane properties of short type blowfly photoreceptors (R1-6) we re investigated in dark and light adaptation with single electrode cur rent and voltage clamp techniques. The impedance of the cells was defi ned in frequency domain by using discontinuous current clamp and white -noise-modulated current injection. We found that the slow activation and relaxation of the voltage-dependent K+ conductance transform the p hotoreceptor membrane effectively into a band-pass filter. This behavi our Could be observed under current clamp as voltage-dependent outward and inward rectification of the membrane. The voltage-dependent band- pass filtering is likely to be present in all neurons with graded pote ntials and voltage-dependent membrane conductances.