Malfunction of respiratory-related neuronal activity in Na+, K+-ATPase α2 subunit-deficient mice is attributable to abnormal Cl- homeostasis in brainstem neurons

Na+, K+-ATPase alpha2 subunit gene (Atp1a2) knock-out homozygous mice (Atp1a2(-/-)) died immediately after birth resulting from lack of breathing. The respiratory-related neuron activity in Atp1a2(-/-) was investigated using a brainstem-spinal cord en bloc preparation. The respiratory motoneuron activity recorded from the fourth cervical ventral root (C4) was defective in Atp1a2(-/-) fetuses of embryonic day 18.5. The C4 response to electrical stimulation of the ventrolateral medulla (VLM) recovered more slowly in Atp1a2(-/-) than in wild type during superfusion with Krebs' solution, consistent with the high extracellular GABA in brain of Atp1a2(-/-). Lack of inhibitory neural activities in VLM of Atp1a2(-/-) was observed by optical recordings. High intracellular Cl- concentrations in neurons of theVLMof Atp1a2(-/-) were detected in gramicidin-perforated patch-clamp recordings. The alpha2 subunit and a neuron-specific K-Cl cotransporter KCC2 were coimmunoprecipitated in a purified synaptic membrane fraction of wild-type fetuses. Based on these results, we propose a model for functional coupling between the Na+, K+-ATPase alpha2 subunit and KCC2, which excludes Cl- from the cytosol in respiratory center neurons.