Purchase this article with an account.
L.A. Cervetto, L. Della Santina, G.C. Demontis, C. Gargini, G.T. Paoli; Distribution and Properties of HCN–Channels in the Retina of Mouse . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3461.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Investigate the role voltage–dependent ion channels play in signal processing by rods and rod–bipolar cells. Methods: ion channel distribution was investigated in mouse (C57Bl6J) retinal sections by immunocytochemistry and confocal microscopy. Voltage–dependent ionic currents were characterized at 37 °C in 150 µ m–thick retinal slices by carrying out voltage–clamp perforated–patch recordings from rods or bipolar cells. Signal processing by the recorded cells was investigated through fast Fourier tramsform (FFT) of the voltage response to current stimuli whose intensity was sinusoidally modulated in time. Results:In rods, two main voltage–dependent currents gate close to the membrane potential in light: the hyperpolarization–activated (Ih) and the depolarization–activated (IKx) currents. Immunocytochemstry indicate the expression at the inner segment, cell body and axon of isoform 1 of hyperpolarization–activated cyclic nucleotide–gated channels (HCN1). At –120 mV Ih time constant of activation is close to 10 ms, consistent with rods expressing HCN1 but not HCN2. The gain of the current–to–voltage conversion in rods is frequency– and voltage–dependent, with the ratio between membrane impedance at 1 and 0.2 Hz, close to 2 at –60 mV and to 0.8 at –40 mV. By comparison, Ih activation time constant is 3–fold slower in bipolar cells than in rods, with half–activation voltage at –90 mV compared with –75 mV in rods. Rod bipolars express HCN2 but not HCN1 isoforms. Intriguingly HCN2 are confined to dendritic "hot spots" in register with presynaptic ribbons, a distribution similar to that of mGLUR6 and KV1.3 channels. Similar to rods, membrane impedance of bipolar cells is frequency– and voltage dependent. The impedance ratio between 1 and 0.2 Hz is close to 1 at –40 mV and is nearly 2 at –60 mV. Conclusions: Although rods and rod–bipolars express HCN isoforms with quite different biophysical properties, at membrane potentials activating Ih their filtering properties are similar, with broad tuning and peak impedance of 2–3 GΩ at 1 Hz. The distribution of HCN2 channels in rod bipolars suggests that each synapse between rod and rod–bipolars will act as a band–pass filter tuned to reduce low–frequency noise while partially compensating low–pass filtering by the transductive cascade.
This PDF is available to Subscribers Only