Cell experiment:

Mouse (m) Slo3 (KCa5.1) channels or mutant forms are expressed in Xenopus oocytes and currents recorded with 2-electrode voltage-clamp. Gain-of-function mSlo3 mutations are used to explore the state-dependence of the inhibition. The interaction between Quinidine hydrochloride monohydrate and mSlo3 channels is modelled by in silico docking[1].

Animal experiment:

24 rats are randomly divided into three groups with eight rats in each group. Groups Q1, Q3, and Q5 receive Quinidine hydrochloride monohydrate 1, 3, and 5 μmol, respectively, in 5 % glucose 0.1 mL. The sciatic nerve is exposed by making an incision from the left sciatic notch to the distal thigh. The subcutaneous tissue is bluntly dissected to expose the biceps femoris. The sciatic nerve is freed from its investing fascia. The procedure is then repeated on the right side. The somato-sensory evoked potential (SSEP) and compound muscle action potentials (CMAP) are recorded at baseline, immediately after Quinidine hydrochloride monohydrate treatment, then every 15 min thereafter for 1 h, then every 30 min thereafter for 3 h. The animals are allowed to recover and then kept separately for 2 weeks. After performing behavioral examinations, electrophysiological examinations are performed with the animals under intra-peritoneal anesthesia[2].

Quinidine hydrochloride monohydrate is a clinical anti-arrythmic drug which is also a potent blocker of K+ channel with an IC50 of 19.9 μM. IC50: 19.9 μM (K+ channel)[1]

Quinidine hydrochloride monohydrate blocks WT mSlo3 (KCa5.1) channels with an IC50 of 19.9±1.41 μM and Hill slope of 1.15±0.15 (n=7). Again, the potency of inhibition by Quinidine hydrochloride monohydrate is higher for F304Y mSlo3 (IC50 of 2.42±0.60 μM, n=9, P<0.005; Hill slope of 0.98±0.12), but lower with R196Q mSlo3 (IC50 of 38.4±6.77 μM, n=5, P<0.001; Hill slope of 1.05±0.16). The inhibition of F304Y mSlo3 by Quinidine hydrochloride monohydrate is observed to have some time dependence[1].

Direct application of Quinidine hydrochloride monohydrate on the sciatic nerve produces a dose-related decrease in amplitude at ascending somato-sensory evoked potential (SSEP) and descending compound muscle action potentials (CMAP) when comparing baseline with other time points, or when comparing the experimental left limb to the right contra-lateral glucose-treated limb. The latencies of SSEPs and CMAP potentials after Quinidine hydrochloride monohydrate applications are increased compare to baseline and the contralateral side[2].

[1]. Wrighton DC, et al. Mechanism of inhibition of mouse Slo3 (KCa 5.1) potassium channels by quinine, quinidine and barium. Br J Pharmacol. 2015 Sep;172(17):4355-63. [2]. Cheng KI, et al. Application of quinidine on rat sciatic nerve decreases the amplitude and increases the latency of evoked responses. J Anesth. 2014 Aug;28(4):559-68.