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 c hanges in Ca2+ can play a signaling role we examined the effects of ra pidly lowering Ca2+ an the excitability of acutely isolated CA1 and cu ltured hippocampal neurons, Reducing Ca2+ excited and depolarized neur ons by activating a previously undescribed nonselective cation channel , This channel had a single-channel conductance of 36 pS, and its freq uency of opening was inversely proportional to the concentration of Ca 2+. The inhibition of gating of this channel Tvas sensitive to ionic s trength but independent of membrane potential, The ability of this cha nnel to sense Ca2+ provides a novel mechanism whereby neurons can resp ond to alterations in the Extracellular concentration of this key sign aling ion.