EFFECT OF ILLUMINATED NIFEDIPINE, A POTENT ANTIOXIDANT, ON INTESTINAL AND VASCULAR SMOOTH MUSCLES

1 The effects of nifedipine (Nif) and its illuminated nitroso product nitrosopine (NTP) were investigated on lipid peroxidation, KCI elevated smooth muscle tension, and ionic currents of single smooth muscle cells. 2 Illumination of Nif at 400-700 nm within 24-48 h changed it completely to a potent antioxidant, NTP. 3 Nif relaxed the KCl-induced contractions of guinea-pig taenia caeci and rat aorta and reduced the amplitude of the evoked inward Ca2+ current of taenia caeci cells in a concentration-dependent manner. NTP (up to 100 M) was ineffective in this respect. Pretreatment by NTP (10 mu M) did not affect the actions of Nif. 4 The evidence suggests that NTP, generated by day-light illumination from Nif, exerts antioxidant activity but is devoid of voltage-dependent Ca2+ channel (VDC) blocking property and does not interfere with the action of Nif on the smooth muscle cell membrane VDC.