Spider venom toxin that shows calcium channel blocking activity and exhibits cytolytic activity by affecting the outer leaflet curvature and/or pore formation across the membrane. It blocks L-type calcium channels (Cav1/CACNA1) in mammalian neurons at nanomolar concentrations. Furthermore, it produces a slow voltage-independent block of mid/low and high voltage-activated calcium channels in cockroach neurons. Potassium ions, histamine, M-ctenitoxin-Cs1a (AC P83619), CSTX-9 (AC P58604), and CSTX-13 (AC P83919) synergistically increase the insecticidal activity of this toxin. In vivo, it causes paralysis in blow flies and provokes death in drosophila. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Belongs to the neurotoxin 19 (CSTX) family.