Identification and properties of bupivacaine-sensitive potassium currents in cultured hippocampal neurons

The aim of this study was to identify and study the properties of a bupivacaine-sensitive potassium current in the plasma membrane of cultured neurons of the rat brain hippocampus. A neuroglial cell culture used in the work was obtained from the brain hippocampus of Wistar rats aged 1–3 days. The neuronal activity was recorded after 10–14 days of culturing. Bupivacaine-sensitive potassium current and the membrane potential (MP) of the analyzed neurons were recorded by the perforated patch-clamp technique. Neurons were identified visually by their morphology, as well as by the pattern of their electrical activity upon depolarizing shifts of the MP. The identified potassium currents were blocked by the application of local anesthetic bupivacaine and non-selective blocker of potassium channels barium and had a reversal potential close to the equilibrium potential for K+. Effects of bupivacaine were fully prevented by Ba2+, while bupivacaine did not completely block the Ba2+ effects, suggesting that bupivacaine affected only a fraction of the Ba2+-blockable membrane channels. Lowering the extracellular pH from 7.4 to 6.3 resulted in an inhibition of the identified potassium current, similarly to the effect of bupivacaine, whereas an increase in the extracellular pH up to 8.2 led to the current augmentation. Current-voltage characteristics for bupivacaine-sensitive potassium current was obtained; at a hyperpolarizing shift of MP to–120 mV the current amplitude was–33 ± 6 pA. The obtained results testify that the properties of bupivacaine-sensitive potassium current in the 10–14-day cultured hippocampal neurons correspond to those of the background 2P potassium channels of the TASK subfamily.