Calcium mobilizing agonists

Synergistic interaction between glucagon and calcium-mobilizing agonists in liver... 

Impaired EC-dependent relaxation may be due to the depletion of l-arginine substrate, the precursor for NO synthesis, possibly accounting for the diminished response of isolated vascular preparations to calcium-mobilizing agonists such as acetylcholine. Several studies have shown that incubation of vessels with L-arginine restores EC-dependent relaxation (Shimokawa et al., 1988 Cooke et al., 1991 Schini and Vanhoutte, 1991). 

Regarding human tissues, the few data available are contradictory, since according to some authors (Tedeschi et al., 1991) histamine release from basophils is not modified by H3 receptor ligands. In other studies (Bent et al., 1991), it was found that thioperamide could increase histamine release from adenoidal mast cells, but apparently (R)a-methylhistamine was totally inactive. In any case the concentrations of thioperamide are much higher than those necessary to block H3 receptors, thus suggesting that other mechanisms might be involved. Raible et al., (1994) hypothesized by the use of thioperamide, the presence of H3 receptors on human eosinophils which mediate histamine-induced increase in cytosolic calcium mobilization. However, the low efficacy of the known H3 receptor agonists, -as stimuli for eosinophils... 

Rao GHR, Krishnamurthi S, Raij L, White JG. Influence of nitric oxide on agonist mediated calcium mobilization in platdets. Biochem Med Md Biol 1990 43 271-275... 

Extension of the N-terminus of RANTES by the chemical coupling of a five-carbon alkyl chain to the oxidized N-terminal Ser residue produces a modified RANTES protein called aminooxy pentane RANTES (AOP-RANTES). This protein was found to have an increased affinity over RANTES and Met-RANTES for CCR5 (34) and in addition has a greater affinity for CCRl and CCR3 (A. Proudfoot, unpublished results). Whereas neither protein-induced chemotaxis of freshly isolated PBMCs, both were capable of calcium mobilization in CHO cells that had been transfected to express high levels of CCR5 receptors (35). Thus modifications of the N terminus of RANTES result in partial agonists, and their ability to induce cellular responses is probably dependent on the number of receptors expressed at the cell surface. 

Because modified RANTES proteins that are unable to induce calcium mobilization and chemotaxis of certain primary cells such as monocytes, yet are capable of inhibiting HIV-1 infection, the mechanism of steric hindrance appeared to be most likely. However, these modified proteins are all capable of receptor activation, and should thus be defined as partial agonists, which does therefore not exclude that receptor activation may play a role. 

Taggart MJ, Wray S 1997 Agonist mobilization of sarcoplasmic reticular calcium in smooth muscle functional coupling to the plasmalemmal Na+/Ca2+ exchanger. Cell Calcium 22 333-341... 

Platelet activation occurs in large part via G protein-coupled agonist receptors and intracellular signaling events that involve activation of phospholipase C (PLC). PLC catalyzes the breakdown of plasma membrane inositol phospholipids, resulting in generation of 1,2-diacylglycerol (DAG) and 1,4,5-inositol triphosphate (IP3). DAG activates protein kinase C, and IP3 induces mobilization of calcium from intracellular stores (10). 

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