Abstract
We have undertaken a quantitative study of the differences in the properties of the fast transient outward current (A-current) between identified neurons of 2 species of nudibranch mollusc. Somata from identifiable neurons of Archidoris montereyensis and Anisodoris nobilis were isolated and voltage-clamped with a 2-microelectrode voltage clamp at 11 degrees C. We examined diversity in the expression of the time- and voltage-dependent properties of A-current by measuring the following parameters: (1) current magnitude, (2) current density, (3) inactivation kinetics, (4) the voltage dependence of steady-state activation and inactivation. We first characterized A-current in each cell type by measuring these parameters for each identified neuron in a series of animals of a given species. The results of these measurements were used to describe the A-current properties of an identified neuron in terms of a mean and SD. The SD measured diversity within the animal population for any given cell type, while the mean values could be compared to measure diversity in the expression of A-current between identified neurons. When we compared mean values for A-current properties between identified neurons of a given species, we did not detect statistically significant differences in the steady-state voltage dependence of activation and inactivation. However, there were statistically significant differences in peak A-current magnitude, density, and inactivation kinetics between identified neurons. We examined differences between the species by comparing the A-current properties of homologous neurons. The major difference between the species was that outward current magnitude and density were significantly greater in Anisodoris than in Archidoris. We conclude that the magnitude and density of A-current differ between identified nudibranch neurons. The neurons also differentially express A-current inactivation kinetics in a cell-specific manner.
