A method using an end point assay for the quantitation of transient intracellular calcium with a set of pairs of protein components having different levels of sensitivity to the concentration of calcium, with broad applicability to many Ca 2+ channel proteins comprising: i) the generation of expression constructs for the fusion proteins having the Ca 2+ /calmodulin dependent protein kinase II (CaMKII) phosphorylation sites of NR2A or NR2B subunits of N-methyl-D-aspartate receptor (NMDAR) or the voltage gated potassium channel of Drosophila (Eag) or any protein sequence which binds to the T-site of CaMKII, conjugated to a mitochondrial localizing signal sequence, or mutants of these sequences; ii) the generation of mammalian expression constructs of α-CaMKII as a chimera with green fluorescent protein (GFP-α-CaMKII) or its mutants; and iii) subjecting to the step of transfection, Ca 2+ stimulation, imaging and quantification of the number of cells with a Ca 2+ -dependent signal; wherein an NMDA receptor activity assay, TRPVI receptor activity assay or GluR4 receptor activity assay is performed to detect the activity of Ca 2+ channel proteins; and wherein the cDNAs of NR2A encoding amino acid residues 1265-1301, or NR2B encoding amino acid residues 1271-1311, or Eag encoding amino acid residues 731-803, harboring the phosphorylation site for CaMKII (Ser 1291, Ser 1303, Thr 787) of NR2A, NR2B and Eag respectively are subcloned into PSGH vector; and wherein the mutants of α-CaMKII and NR2B or NR2A are selected from: T286D-α-CaMKII and mitochondrial localisation sequence -WT-NR2B, F293E/N294D-α-CaMKII and MLS-WT-NR2B, S1303A-NR2B and WT-α-CaMKII, K42R/T286D-α-CaMKII and MLS-WT-NR2B, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and WT-α-CaMKII, MLS-(S1291A)/Delta IN (deletion of Ile 1286 -Asn 1287 motif of NR2A) NR2A and WT-α-CaMKII, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and a286D-α-CaMKII, and Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and T286D-α-CaMKII, wherein the sequences of NR2A, NR2B and Eag form parts of fusion proteins with a mitochondrial targeting signal sequence, a myc-epitope and GST at the N-terminal end, MLS-NR2A, MLS-NR2B or MLS-Eag; and wherein a specific method of quantification is used by taking the total number of green fluorescent cells which develop punctae as a signal for intracellular calcium release and representing it as percentage of the total number of green fluorescent cells. i) the generation of expression constructs for the fusion proteins having the Ca 2+ /calmodulin dependent protein kinase II (CaMKII) phosphorylation sites of NR2A or NR2B subunits of N-methyl-D-aspartate receptor (NMDAR) or the voltage gated potassium channel of Drosophila (Eag) or any protein sequence which binds to the T-site of CaMKII, conjugated to a mitochondrial localizing signal sequence, or mutants of these sequences; ii) the generation of mammalian expression constructs of α-CaMKII as a chimera with green fluorescent protein (GFP-α-CaMKII) or its mutants; and iii) subjecting to the step of transfection, Ca 2+ stimulation, imaging and quantification of the number of cells with a Ca 2+ -dependent signal; wherein an NMDA receptor activity assay, TRPVI receptor activity assay or GluR4 receptor activity assay is performed to detect the activity of Ca 2+ channel proteins; and wherein the cDNAs of NR2A encoding amino acid residues 1265-1301, or NR2B encoding amino acid residues 1271-1311, or Eag encoding amino acid residues 731-803, harboring the phosphorylation site for CaMKII (Ser 1291, Ser 1303, Thr 787) of NR2A, NR2B and Eag respectively are subcloned into PSGH vector; and wherein the mutants of α-CaMKII and NR2B or NR2A are selected from: T286D-α-CaMKII and mitochondrial localisation sequence -WT-NR2B, F293E/N294D-α-CaMKII and MLS-WT-NR2B, S1303A-NR2B and WT-α-CaMKII, K42R/T286D-α-CaMKII and MLS-WT-NR2B, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and WT-α-CaMKII, MLS-(S1291A)/Delta IN (deletion of Ile 1286 -Asn 1287 motif of NR2A) NR2A and WT-α-CaMKII, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and a286D-α-CaMKII, and Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and T286D-α-CaMKII, wherein the sequences of NR2A, NR2B and Eag form parts of fusion proteins with a mitochondrial targeting signal sequence, a myc-epitope and GST at the N-terminal end, MLS-NR2A, MLS-NR2B or MLS-Eag; and wherein a specific method of quantification is used by taking the total number of green fluorescent cells which develop punctae as a signal for intracellular calcium release and representing it as percentage of the total number of green fluorescent cells. T286D-α-CaMKII and mitochondrial localisation sequence -WT-NR2B, F293E/N294D-α-CaMKII and MLS-WT-NR2B, S1303A-NR2B and WT-α-CaMKII, K42R/T286D-α-CaMKII and MLS-WT-NR2B, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and WT-α-CaMKII, MLS-(S1291A)/Delta IN (deletion of Ile 1286 -Asn 1287 motif of NR2A) NR2A and WT-α-CaMKII, MLS-Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and a286D-α-CaMKII, and Delta IN NR2A (deletion of Ile 1286 -Asn 1287 motif of NR2A) and T286D-α-CaMKII,