Table 1.

Ca2+ affinities in excitatory and inhibitory synapses

GenotypeKd (mm Ca2+) (±SEM)nImaxEPSC/IPSCNormalization
Inter-neuronal synapses
    Wild type1.9 ± 0.32.57.4 nAIPSCNone
    Syt-1 D232N1.2 ± 0.12.88.2 nAIPSCNone
    Wild type1.7 ± 0.23.07.3 nAIPSCNone
    Syt-1 D238N1.8 ± 0.32.46.7 nAIPSCNone
Autapses
    Syt-1 D232N1.0 ± 0.01.81.4EPSCTo 4 Ca2+/4 Mg2+ EPSC
    Syt-1 D238N1.8 ± 0.22.01.9EPSCTo 4 Ca2+/4 Mg2+ EPSC
    Syt-1 D232N1.0 ± 0.01.81.0EPSCTo maximal EPSC
    Syt-1 D238N1.7 ± 0.12.31.0EPSCTo maximal EPSC
Autapses (Fernandez-Chacon et al., 2001)
    Wild type1.9 ± 0.21.71.7EPSCTo 4 Ca2+/4 Mg2+ EPSC
    Syt-1 R233Q3.7 ± 0.81.61.3EPSCTo 4 Ca2+/4 Mg2+ EPSC
  • Apparent Ca2+ affinities were determined by measuring the amplitudes of synaptic responses as a function of the extracellular Ca2+ concentration (all in the presence of 1 mm Mg2+ for autapses and 0.8 mm Mg2+ for inter-neuronal synapses). Responses were fitted to a Hill function as follows: I = I0 + (ImaxI0)/(1+ (Kd/[Ca2+])), where I is the recorded synaptic current plotted as normalized amplitude, I0 is the base value of responses, Imax is the maximal current, Kd is the apparent dissociation constant for extracellular Ca2+, [Ca2+] is the extracellular Ca2+ concentration, and n is the apparent cooperativity. For all fits, I0 was set to 0. Data shown are from Figures 6 and 10, and from Fernandez-Chacon et al. (2001). Wild-type values are always obtained from cultures from littermate mice plated and measured on the same day as the mutant. Syt-1, Synaptotagmin-1.