Altered pH Homeostasis and Acoustic Induced Seizures Associated with Kcnj16 Loss of Function Mutation
Burgraff N, Pavlov T, Levchenko V, Geurts A, Forster H, Staruschenko A, Hodges M, and Palygin O. Altered pH homeostasis and acoustic induced seizures associated with KCNJ16 loss of function mutation. FASEB Journal 2017; 31(1 Suppl):1072.7.
Medullary neurons expressing pH sensitive potassium channels have been proposed to play a role in cellular pH chemosensitivity and CO2/pH homeostasis, but the specific potassium channels that contribute remain to be elucidated. One candidate is the inward rectifier K+ channel subunit Kir5.1 (Kcnj16), due to its expression in pH sensitive medullary neurons. Herein, we have studied breathing, temperature, and seizure activity in rats with a genetic disruption of the Kcnj16 gene, encoding the Kir5.1 channel. Zinc finger nuclease was used to create an 18 base pair deletion of the Kcnj16 gene on chromosome 10 in the Dahl salt-sensitive rat (SSKcnj16-/-), leading to disruption of the transmembrane 2 domain of the Kir5.1 channel. To test for alterations in CO2 chemosensitivity, SSKcnj16-/- and control SS rats were exposed to increasing levels of inspired CO2 (InCO2) of 3, 5, 7, and 9% CO2. In control SS animals, ventilation increased 40.4 ml/min/mmHg, as compared to 25.8 ml/min/mmHg in SSKcnj16-/-. Therefore, this data allows us to conclude that SSKCNJ16-/- rats showed an attenuated ventilatory response to increasing levels of InCO2, consistent with the notion of Kir5.1-containing channels playing a role in central chemosensitivity. SSKcnj16-/- rats also presented with an epileptic phenotype characterized by acoustic induced seizures that lead to apnea and alterations in body temperature. Upon investigation of seizure activity, SSKcnj16-/- were highly susceptible to 10 kHz sound stimulation (86 dB for 2 minutes), resulting in generalized tonic-clonic convulsions, with pronounced apnea and increases in body temperature during seizure activity. Following seizure activity, body temperature remained elevated (up to +1.7°C) for hours, along with significant increases in total ventilation (VE) above control levels (VE was 238.3±5.1% and 124.4±10.6% above baseline 5 and 20 min post-stimulation, respectively; N=6). EEG telemetry revealed large increases in the frequency of brain activity during sound stimulation that was consistent with seizure activity. Seizure severity was scored according to Racine's scale from 0 to 4 (0 - no seizures; 1 - headlong running and chaotic jumping; 2 - rearing with forelimb clonus; 3 - motor excitation followed by clonic seizures in a position on the belly; 4 - three previous phases followed by tonic seizures and loss of consciousness) with a mean score of 2.4±0.3 (N=12). In SS rats, audiogenic stimulation has apparently no effect. Repeated sound stimulation (every week during 3-4 weeks) did not result in adaptation of seizure activity, and acute intraperitoneal administration of 2.5 mg/kg diazepam prior to sound stimulation abolished seizure activity in SSKcnj16-/- rats. In conclusion, disruption of Kir5.1 containing-channels leads to alterations in the ventilatory response to increasing levels of InCO2, and an acoustic induced epileptic phenotype.