Potassium currents are an important factor in repolarizing the membrane potential and determining the level of neuronal excitability. We compared potassium currents in CA1 hippocampal neurons dissociated from young (2-3 months old) and old (26-30 months old) Sprague-Dawley rats. Whole-cell patch-clamp techniques were used to measure the delayed rectifier (sustained) and the A-type (transient) potassium currents. The delayed rectifier current was smaller in old (548 +/- 57 pA) than in young (1193 +/- 171 pA) neurons. In the absence of extracellular calcium, the delayed rectifier current was also smaller in old (427 +/- 41 pA) than in young (946 +/- 144 pA) neurons. The cell membrane capacitance was unchanged in old (13.3 +/- 1.2 pF) compared to young (13.6 +/- 1.2 pF). Therefore, the reduction in the delayed rectifier current was not due to a change in membrane surface area. Moreover, activation and inactivation of the delayed rectifier current were unchanged in old compared to young neurons. The slope of the current-voltage relation, however, was smaller in old (B = 5.03) than in young (B = 9.62) neurons. Similarly, the A-current was smaller in old (100 +/- 16 pA) than in young (210 +/- 44 pA) neurons in the presence of extracellular calcium. This reduction of potassium currents could account for the prolongation of action potentials reported previously for old rat CA1 hippocampal neurons. The age-related reduction in potassium current indicates plasticity in neuronal function that can impact communication in the hippocampal neural network during aging.
Copyright 2001 Wiley-Liss, Inc.