fm1-43 and 1-4-dihydropyridine

Purinergic stimulation of surfactant secretion via exocytosis of lamellar bodies is mediated by an elevation of the intracellular Ca2+ concentration ([Ca2+](i)). We tested the dihydropyridine (DHP) analogues isradipine (+/-enantiomers), nifedipine and Bay K 8644 (racemic forms) on ATP-induced surfactant secretion and [Ca2+](i) in single type II cells, using FM1-43 and fura-2 fluorescence. None of the DHPs (2 microM) had an effect on ATP-induced surfactant secretion in the dark. They did, however, inhibit secretion in a concentration-dependent manner during illumination, particularly with UV light. This effect was not stereospecific, because it was mimicked by (-)-isradipine. In addition, (+)- or (-)-isradipine, but not nifedipine or Bay K 8644, elicited a slow increase of [Ca2+](i) during illumination with UV light, which was reversible by exposure to dark. None of the DHPs inhibited the ATP-induced Ca2+ signal. In perforated patch clamp experiments, depolarizing voltage steps did not induce L-type Ca2+ (Sr(2+)) currents, even in the presence of the agonist Bay K 8644 (1 microM). We conclude that impairment of ATP-induced surfactant secretion by all tested DHPs and alterations of Ca2+ homeostasis by isradipine are photoactivated effects, independent of L-type Ca2+ channels.

Topics: Adenosine Triphosphate; Animals; Calcium; Calcium Channel Blockers; Calcium Channels, L-Type; Dihydropyridines; Drug Interactions; Exocytosis; Fura-2; In Vitro Techniques; Light; Male; Molecular Conformation; Photochemistry; Pulmonary Alveoli; Pyridinium Compounds; Quaternary Ammonium Compounds; Rats; Rats, Sprague-Dawley; Strontium; Surface-Active Agents