Deficient Cation Channel Regulation in Neurons From Mice With Targeted Disruption of the Extracellular Ca-Sensing Receptor Gene

This study presents evidence that a receptor sensitive to the concentration of extracellular Ca²⁺ (Ca²⁺_o) (CaR) is functionally coupled to ion channels involved in modulation of neuronal excitability. This receptor is expressed in hippocampus and other brain regions, suggesting that it could mediate some of the well-recognized but poorly understood direct actions of extracellular Ca²⁺ (Ca²⁺_o) on neuronal function. The effects of polycationic CaR agonists on the activity of a nonselective cation channel (NCC) in cultured hippocampal neurons from wild-type mice and from mice homozygous for targeted disruption of the CaR gene (CaR −/−) were compared in this study. The CaR agonists, neomycin (100 μM), spermine (300 μM), and elevation of Ca²⁺_o from 0.75 to 3 mM, significantly increased the probability of channel opening (Po) in wild-type neurons. None of these agents, however, produced any effect on Po in neurons from mice lacking the CaR. The same NCC, however, could be activated by thapsigargin in neurons from both wild-type mice and CaR-deficient mice, most likely through an associated increase in the cytosolic free calcium concentration (Ca_i). Thus the CaR regulates the activity of Ca²⁺-permeable NCC in hippocampal neurons and could potentially modulate key neuronal functions, including neurotransmission and neuronal excitability, via membrane depolarization.