Model for cAMP and Ca²⁺ mediated signaling pathways that regulate microneme secretion in P falciparum merozoites.

Exposure of P. falciparum merozoites to low K⁺ environment as present in blood plasma leads to production of H⁺ and HCO₃⁻ ions by carbonic anhydrase (CA) to maintain pH. HCO₃⁻ ions activate cytoplasmic adenylyl cyclase (ACβ) leading to rise in cytosolic levels of cAMP. Elevation of cAMP activates its downstream effectors PKA and Epac. Epac activates Rap1 by transferring GTP. Rap1-GTP activates PLC leading to rise in cytosolic Ca²⁺ levels, which leads to activation of calcium dependent protein kinase 1 (CDPK1) and calcium dependent phosphatase, calcineurin (CN), both of which directly play roles in microneme secretion. Mn, micronemes; Rh, rhoptries.