Characterisation of the effects of SR146131, a novel non-peptide CCK(1) receptor agonist, on IMR-32 human neuroblastoma cells

The effect of ?2-4-(4-chloro-2, 5-dimethoxy-phenyl)-5-2-cyclohexyl-ethyl)-thiazol-2-ylcarbamoy l]-5, 7-dimethyl-indol-1-yl?-acetic acid (SR146131), a novel non-peptide agonist of cholecystokinin (CCK) CCK(1) receptors, was compared to the effect of sulphated cholecystokinin octapeptide (CCK-8-S) on CCK(1) receptors of the human neuroblastoma cell line IMR-32. SR146131 inhibited 125I]CCK-8-S binding to IMR-32 cells at nanomolar concentrations. SR146131 and CCK-8-S increased intracellular free Ca(2+) levels (Ca(2+)](i)) in the same concentration range (EC(50)=6+/-2.3 and 1.3+/-0.14 nM, respectively). Although the shape of the Ca(2+)](i) increase induced by CCK-8-S and SR146131 was slightly different, extracellular Ca(2+) removal affected the response of both compounds to a similar degree, and the response of both compounds was essentially due to Ca(2+) release from intracellular stores. This was also confirmed by measuring the Ca(2+)](i) response of single cells: both compounds induced Ca(2+)](i) oscillations at subnanomolar concentrations and elicited a large peak increase in Ca(2+)](i) at higher concentrations (EC(50)=0.5+/-0.04 and 5.7+/-1.9 nM for CCK-8-S and SR146131, respectively). Both CCK-8-S and SR146131 induced a sustained increase of phosphoinositide turnover in these cells, and acted at similar concentrations (EC(50)=2.7+/-0.7 and 6+/-3.1 nM, respectively), although the maximal effect of SR146131 was somewhat lower than the effect of CCK-8-S. These data show that SR146131 activates human CCK(1) receptors on IMR-32 cells in a manner and with a potency similar to that of CCK-8-S.