Ca2+ entry mediated by store depletion, S-nitrosylation and TRP3 channels - Comparison of coupling and function

The mechanism for coupling between Ca2+ stores and store-operated channels (SOCs) is an important but unresolved question. SOC-mediated Ca2+ entry is complex and may reflect more than one type of channel and coupling mechanis m. To assess such possible divergence the function and coupling of SOCs was compared with two other distinct yet related Ca2+ entry mechanisms. SOC co upling in DDT1MF-2 smooth muscle cells was prevented by the permeant inosit ol 1,4,5-trisphosphate (InsP(3)) receptor blockers, 2-aminoethoxydiphenyl b orate (2-APB) and xestospongin C. In contrast, Ca2+ entry induced by S-nitr osylation and potentiated by store depletion (Ma, H-T., Favre, C. J., Patte rson, R. L., Stone, M. R., and Gill, D. L. (1999) J. Biol Chem. 274, 35318- 35324) was unaffected by 2-APB, suggesting that this entry mechanism is ind ependent of InsP(3) receptors. The cycloalkyl lactamimide, MDL-12,330A (MDL ), prevented SOC activation (IC50 10 mu M) and similarly completely blocked S-nitrosylation-mediated Ca2+ entry. Ca2+ entry mediated by the TRP3 chann el stably expressed in HEK293 cells was activated by phospholipase C-couple d receptors but independent of Ca2+ store depletion (Ma, B-T., Patterson, R . L., van Rossum, D. B., Birnbaumer, L., Mikoshiba, K., and Gill, D. L. (20 00) Science 287, 1647-1651). Receptor-induced TRP3 activation was 2-APB-sen sitive and fully blocked by MDL. Direct stimulation of TRP3 channels by the permeant diacylglycerol derivative, 1-oleoyl-2-acetyl-sn-glycerol, was not blocked by 2-APB, but was again prevented by MDL. The results indicate tha t although the activation and coupling processes for each of the three entr y mechanisms are distinct, sensitivity to MDL is a feature shared by all th ree mechanisms, suggesting there may be a common structural feature in the channels themselves or an associated regulatory component.