Effect of Extracellular HCO3 2 on Na Channel Characteristics in Hippocampal CA1 Neurons

Gu, Xiang Q., Hang Yao, and Gabriel G. Haddad. Effect of extracellular HCO3 2 on Na channel characteristics in hippocampal CA1 neurons. J Neurophysiol 84: 2477–2483, 2000. The effect of HCO3 /CO2 on membrane properties of isolated hippocampal CA1 neurons was studied with the use of the whole cell configuration of the patch-clamp technique. Neurons were acutely dissociated from 21to 30-day-old mice. In the current-clamp mode, HCO3 /CO2 significantly hyperpolarized CA1 neurons by more than 10 mV and decreased their input resistance. In addition, the overall excitability of these neurons was lower in the presence of HCO3 /CO2 than in HEPES. Spontaneous and evoked action potential firing frequency was lower in the presence of HCO3 /CO2 than in its absence. In the voltage-clamp mode, both activation and steady-state inactivation of a fast Na current were shifted in the hyperpolarized direction in such a way that the window currents were smaller in HCO3 /CO2 than in HEPES. Recovery from inactivation and deactivation from the open state of the fast Na current was slower in HCO3 /CO2 than in HEPES. We conclude that HCO3 /CO2 decreases the intrinsic excitability of CA1 neurons by altering not only the passive properties of the neuronal membranes but also by changing several characteristics of the fast Na current, including activation and inactivation kinetics as well as the recovery from inactivation and deactivation.