Shunt peaking in neural membranes.
Capacitance limits the bandwidth of engineered and biological electrical circuits because it determines the gain-bandwidth product (GBWP). With a fixed GBWP, bandwidth can only be improved by decreasing gain. In engineered circuits, an inductance reduces this limitation through shunt peaking but no equivalent mechanism has been reported for biological circuits. We show that in blowfly photoreceptors a voltage-dependent K+conductance, the fast delayed rectifier (FDR), produces shunt peaking thereby increasing bandwidth without reducing gain. Furthermore, the FDR's time constant is close to the value that maximizes the photoreceptor GBWP while reducing distortion associated with the creation of a wide-band filter. Using a model of the honeybee drone photoreceptor, we also show that a voltage-dependent Na+conductance can produce shunt peaking. We argue that shunt peaking may be widespread in graded neurons and dendrites.
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK fjhheras@gmail.com.
Francisco J H
0000-0001-8124-2359
FJ
Heras
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
Simon B
SB
Laughlin
School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK.
Jeremy E
JE
Niven
D000818:Animals; D001516:Bees / Q000502:physiology*; D025802:Electric Capacitance; D019476:Insect Proteins / Q000378:metabolism; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D061566:Voltage-Gated Sodium Channels / Q000378:metabolism
D019476:Insect Proteins; D024642:Potassium Channels, Voltage-Gated; D061566:Voltage-Gated Sodium Channels
biophysical constraints; gain–bandwidth product; insect photoreceptor; membrane capacitance; phenomenological inductance; voltage-dependent conductances