Early receptor potentials and comparison of the electrical properties of median and lateral photoreceptors of the barnacle

Abstract

Extracellular recordings of the early receptor potential (ERP) from Balanus eburneus revealed that the response of the median photoreceptor is faster by a factor of two than that of the lateral photoreceptor. This difference is similar to that shown for late receptor potentials (LRP) from both types of photoreceptor. A model for the photoreceptors is given which takes the electrical properties of the microvillar and perikaryon membrane areas as determining the time courses of the ERP responses. The perikaryon areas emerge with a specific membrane resistance of 1000 Ωcm 2, a value commonly found for nerve membranes, and as the dominant cell resistance. The microvillar areas have a specific membrane resistance of about 25 kΩ cm 2, and their large surface areas determine the large capacities of the cells. A specific capacitance of about 1 μF/cm 2 was measured for both types of membrane in median and lateral photoreceptors. The difference in ERP time course of the two types of photoreceptors is attributed to different proportioning of microvillar and perikaryon areas. Good agreement between calculated and observed ERP responses was found.