... GATCATGCACTGAAATTTA (2), GATGAAACCTCTCAAACTG (3), and CATCATCGCTGGACAATGT (4)], usingT. R. Dunkern and A. Hatzelmann Characterization of inhibitors of PDE1CFEBS Journal 274 (2007) 4812–4824 ª 2007 The ... ionomycin at these higher concentra-tions. The addition of 50 mm EGTA (as a control) at the end of the experiment (indicated by a solid arrowin Fig. 4A) decreased the Ca2+signal. On the basis of these ... lL of a substrate solution (Promega, Madison, WI,USA; CytoTox96 assay), and after 15 min of incubation,an additional 50 lL of a stop solution. Thereafter, extinctionwas measured at a wavelength...