Wavelength sensitivity of the two components of the early receptor potential (ERP) of the human eye

The early receptor potential (ERP)

The ERP contains information on the function of the outer segments of the retinal photoreceptors. The authors have established normative values of the ERP and the factors which might be of influence hereupon. ERP findings in patients suffering from various eye diseases are given. Value and limitation of ERP recording are discussed in relation to the other clinically available electrodiagnostic tests.

Early receptor potential recordings for clinical routine

An apparatus and an electrode for early receptor potential recordings in clinical routine are introduced. One-hundred and eighty normal eyes were compared with cases of diffuse and localized retinal diseases. In retinitis pigmentosa patients a decrease in R1 and R2 amplitudes and in some cases a much faster time course was found. Eyes with circumscribed retinal affectations produced a wide variety of amplitudes, overlapping with the range of normals. In cases of monochromatism, the ERP recording established the diagnosis because of an absent R1 wave.

On the rise time of the R1-component of the "early receptor potential": evidence for a fast light-induced charge separation in rhodopsin

The rising phase of the R1-component of the early receptor potential from isolated cattle retinas was measured with high time resolution. When the measuring capacitance was 133 pF, a latency of about 200 ns was observed. A rise time of about 0.8 mus at 0 degrees C and 1.6 mus at 37 degrees C (extrapolated to ideal measuring conditions) was found. The negative temperature dependence indicates that the rise is not directly related to the production and decay of photolysis products of rhodopsin since the latter have positive temperature coefficients. An increase of the external measuring capacitance caused a slower rise time. The analysis of this effect allowed the determination of the source impedance of the R1-component. The experimental results can be described with a model in which it is assumed that a fast charge separation (ns or ps) takes place in the outer segment of a photoreceptor cell, and spreads passively to the inner segment via the resistance of the interconnecting cilium. The "inner" relaxation could be circumvented by using isolated rod outer segments which lack the passive inner segments, i.e., a rise time of 90 ns could be measured when isolated rod outer segments were attached to Millipore filters. The results suggest that the molecular event leading to the R1-component is an early charge separation which may be as fast as the cis-trans isomerization of the retinal chromophore.