Lactate reduces epileptiform activity through HCA1 and GIRK channel activation in rat subicular neurons in an in vitro model

Objective Much evidence suggests that the subiculum plays a significant role in the regulation of epileptic activity. Lactate acts as a neuroprotective agent against many conditions that cause brain damage. During epileptic seizures, lactate formation reaches up to similar to 6 mmol/L in the brain. We investigated the effect of lactate on subicular pyramidal neurons after induction of epileptiform activity using 4-aminopyridine (4-AP-0Mg(2+)) in an in vitro epilepsy model in rats. The signaling mechanism associated with the suppression of epileptiform discharges by lactate was also investigated. Methods We used patch clamp electrophysiology recordings on rat subicular neurons of acute hippocampal slices. Immunohistochemistry was used for demonstrating the expression of hydroxycarboxylic acid receptor 1 (HCA1) in the subiculum. Results Our study showed that application of 6 mmol/L lactate after induction of epileptiform activity reduced spike frequency (control 2.5 +/- 1.23 Hz vs lactate 1.01 +/- 0.91 Hz, P = .049) and hyperpolarized the subicular neurons (control -51.8 +/- 1.9 mV vs lactate -57.2 +/- 3.56 mV, P = .002) in whole cell patch-clamp experiments. After confirming the expression of HCA1 in subicular neurons, we demonstrated that lactate-mediated effect occurs via HCA1 by using its specific agonist. All values are mean +/- SD. Electrophysiological recordings revealed the involvement of G beta gamma and intracellular cAMP in the lactate-induced effect. Furthermore, current-clamp and voltage-clamp experiments showed that the G protein-coupled inwardly rectifying potassium (GIRK) channel blocker tertiapin-Q, negated the lactate-induced inhibitory effect, which confirmed that lactate application results in outward GIRK current. Significance Our finding points toward the potential role of lactate as an anticonvulsant by showing lactate-induced suppression of epileptiform activity in subicular neurons. The study gives a different insight by suggesting importance of endogenous metabolite and associated signaling factors, which can aid in improving the present therapeutic approach for treating epilepsy.