Mamba venoms contain peptides with high selectivity for muscarinic receptors, Due to the limited availability of the M-1 muscarinic receptor-selective MT7 or ml-toxin 1, the peptide was expressed in Sf9 cells using a synthetic cDNA and purified, The isolated peptide had over four orders of magnitude higher affinity for the M-1 compared to M-2-M-5 muscarinic receptors, The peptide strongly inhibited Ca2+ mobilisation ;through recombinant and endogenously expressed M-1 receptors, having no effect on the function of the other subtypes. The MT7 peptide provides a unique tool for identification and functional characterisation of M-1 receptors in cells and tissues,