2-(3,4-Dimethoxyphenyl)-2-isopropyl-5-[N-[4-(N-methyl-2-diazo- 3,3,3-trifluoropropionamido)phenethyl]methyl-amino]valeronitril e (3), a potential photoaffinity probe for Ca2+ channels related to verapamil (1), was prepared from N-methyl-4-nitrophenethylamine (7) and 2-(3,4-dimethoxyphenyl)-2-isopropyl-5-(methanesulfonoxy)valeron itrile (12). Compound 3 showed concentration-dependent negative inotropic effects in rat right myocardial ventricular strips, EC50 = (1.05 +/- 0.33) X 10(-7) M (mean +/- SD), being slightly less potent than gallopamil (2), EC50 = (2.18 +/- 0.66) X 10(-8) M. It displaced [3H]gallopamil in myocardial membranes, Ki = (3.76 +/- 1.55) X 10(-8) M, compared to 2, Ki = (1.55 +/- 0.16) X 10(-8) M. Photoactivation at 265 nm reduced the recoverable binding of [3H]gallopamil to 26% compared to no effect on 2. This agent may be a useful photoaffinity probe to aid in further characterization of Ca2+ channels.