Alpha-conotoxins act on postsynaptic membranes, they bind to the nicotinic acetylcholine receptors (nAChR) and thus inhibit them. Has weak blocking effects on muscle nAChR composed of alpha-1/beta-1/gamma/delta subunits and the central nervous system nAChR composed of alpha-4/beta-2 subunits. Does not detectably affect the peripheral nervous system nAChR composed of alpha-3/beta-4 subunits. Low toxin concentrations potentiate currents in muscle nAChR composed of alpha-1/beta-1/gamma/delta subunits and central nervous system nAChR composed of alpha-4/beta-2 subunits, but not the peripheral nervous system nAChR composed of alpha-3/beta-4 subunits. Expressed by the venom duct. The cysteine framework is I (CC-C-C). Alpha4/7 pattern. Occurs in 2 forms which differ in the post-translational modification of Glu-60. In form SrA1 Glu-60 is 4-carboxyglutamate while in form SrA2 Glu-60 is unmodified. Conotoxin Sr1A, with 4-carboxyglutamate at Glu-60. Conotoxin Sr1B, without 4-carboxyglutamate at Glu-60. Belongs to the conotoxin A superfamily.