Relative contribution of two mechanisms to post-stimulus hyperpolarization in leech retzius cells

Abstract 1. 1. In Retzius cells of the horse leech, Haemopis sanguisuga , intensive firing is followed by prolonged post-stimulus hyperpolarization (PSH) mediated by an increase in K-conductance and activation of the electrogenic sodium pump. 2. 2. The recovery of membrane potential during PSH can be described by a biexponential model from which the relative contribution of the early and the late component to the peak amplitude of PSH may be calculated. 3. 3. The time course of the calculated early component coincides with the time course of changes that occur in input membrane resistance during PSH. 4. 4. The relative contribution of the late component increases linearly with an increase in stimulus duration. The rate constants of the two phases did not change with changes in stimulus duration. 5. 5. It was concluded that the proposed model is useful for the estimation of the relative contribution and kinetics of two PSH mediating mechanisms (K-conductance increase and activation of an electrogenic sodium pump) in different experimental conditions.