Reduced potassium currents in old rat CA1 hippocampal neurons

Potassium currents are an important factor in repolarizing the membrane pot ential and determining the level of neuronal excitability. We compared pota ssium currents in CA1 hippocampal neurons dissociated from young (2-3 month s old) and old (26-30 months old) Sprague-Dawley rats. Whole-cell patch-cla mp techniques were used to measure the delayed rectifier (sustained) and th e 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 als o smaller in old (427 +/- 41 pA) than in young (946 +/- 144 pA) neurons. Th e 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 rectif ier current was not due to a change in membrane surface area. Moreover, act ivation 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. Si milarly, the A-current was smaller in old (100 +/- 16 pA) than in young (21 0 +/- 44 pA) neurons in the presence of extracellular calcium. This reducti on of potassium currents could account for the prolongation of action poten tials reported previously for old rat CA1 hippocampal neurons. The age-rela ted reduction in potassium current indicates plasticity in neuronal functio n that can impact communication in the hippocampal neural network during ag ing. (C) 2001 Wiley-Liss, Inc.