Background:

Calmidazolium (chloride) is an inhibitor of calmodulin (CaM), inhibiting CaM-dependent phosphodiesterase and CaM-induced activation of erythrocyte calcium-transporting ATPase (IC50 = 0.15 and 0.35 μM, respectively).[1] Calmidazolium also inhibits an array of calcium-transporting ATPases, including those from heart and skeletal muscle (IC50 = 2.1 and 2.9 μM, respectively).[1] It also induces the influx of extracellular calcium through store-operated calcium channels (EC50 = 3 μM).[2],[3]

Reference:
[1]. Gietzen, K. Comparison of the calmodulin antagonists compound 48/80 and calmidazolium. Biochemistry Journal 216(3), 611-616 (1983).
[2]. Harper, J.L., and Daly, J.W. Effect of calmidazolium analogs on calcium influx in HL-60 cells. Biochemical Pharmacology 60(3), 317-324 (2000).
[3]. Peppiatt, C.M., Holmes, A.M., Seo, J.T., et al. Calmidazolium and arachidonate activate a calcium entry pathway that is distinct from store-operated calcium influx in HeLa cells. Biochemistry Journal 381(3), 929-939 (2004).