A new method for evaluating sigma(2) ligand activity in the isolated guinea-pig bladder.

We demonstrated the presence of sigma(2) receptors in the guinea-pig ileum by saturation analysis and extended our investigation to guinea-pig bladder and rat bladder. In functional assays of the isolated tissues in organ baths, sigma(2) receptor ligands inhibited electrically evoked contractions in both guinea-pig bladder and ileum and a linear correlation was found between sigma(2) receptor affinity and sigma(2) receptor activity values of selected compounds. The sigma(2) activity of these compounds in the presence of desensitised sigma(1) receptors both in bladder and ileum was also tested. On the basis of our results, we propose the electrically stimulated guinea-pig bladder as a new method for evaluating sigma(2) activity.