Extracellular calcium sensed by a novel cation channel in hippocampal neurons

Extracellular concentrations of Ca2+ change rapidly and transiently in the brain during excitatory synaptic activity, To test whether such changes in Ca2+ can play a signaling role we examined the effects of rapidly lowering Ca2+ an the excitability of acutely isolated CA1 and cultured hippocampal neurons, Reducing Ca2+ excited and depolarized neurons by activating a previously undescribed nonselective cation channel, This channel had a single-channel conductance of 36 pS, and its frequency of opening was inversely proportional to the concentration of Ca2+. The inhibition of gating of this channel Tvas sensitive to ionic strength but independent of membrane potential, The ability of this channel to sense Ca2+ provides a novel mechanism whereby neurons can respond to alterations in the Extracellular concentration of this key signaling ion.