CaM I activators encompass a diverse array of chemical compounds that exert their effects by modulating intracellular signaling pathways, thus influencing the functional activity of CaM I. Forskolin, by raising cAMP levels, indirectly activates CaM I through PKA-mediated phosphorylation events. Similarly, FTY720, once phosphorylated, can engage S1P receptors, altering Ca2+ signaling which is intimately connected with the CaM I activation state. A23187, by increasing intracellular calcium, directly influences CaM I's calcium-binding ability, a crucial determinant of its activity. PMA and IBMX both foster an environment conducive to CaM I activation; the former through PKC pathway activation and the latter by inhibiting cAMP degradation, thereby sustaining PKA activity.
Meanwhile, PMA and OAG act as activators of protein kinase C (PKC), which can lead to increased intracellular calcium levels, thereby directly enhancing the activity of CaM I, which is sensitive to calcium levels. Sphingosine-1-phosphate (S1P) and Ryanodine influence intracellular calcium stores with S1P activating its receptors to release calcium while Ryanodine modulates ryanodine receptors to similar effect, both leading to increased CaM I activation. Thapsigargin contributes to this process byinhibiting SERCA, causing a rise in cytosolic calcium levels, which would directly result in increased CaM I activity. Ionophore A23187 directly increases intracellular calcium concentration, providing a straightforward mechanism to enhance CaM I activity. Nifedipine, by blocking L-type calcium channels, alters calcium signaling and can lead to enhanced CaM I activity through the increase of intracellular calcium.