“Furthermore, quinidine inhibits rather than stimulates binding of tritiated nitrendipine , nimodipine or (S)-isradipine to isolated cardiac membranes.”
“The negative inotropic potency of nitrendipine is clearly enhanced by quinidine (3·10−6-10−4 mol/l) by up to two orders of magnitude, i.e. cardiac nitrendipine effects are potentiated.”