Abstract
Interactions of theβ-blocker drug, propranolol, with amphipathic systems have been studied using fluorescence spectroscopy. The results show a strong binding of propranolol with micelles of sodium dodecyl sulfate revealed through changes in the fluorescence spectrum and an increase in fluorescence lifetime. Quenching of propranolol fluorescence by iodide is used to demonstrate interaction withβ-cyclodextrin. At high concentrations, self-quenching of propranolol fluorescence was also observed withκq=2.5×109dm3mol–1s–1. Two-photon excited (630 nm) fluorescence lifetime imaging of propranolol in cells showed propranolol to be widely distributed in the cell cytoplasm, with fluorescence lifetimes shorter than in solution. The results suggest that intracellular propranolol is mainly confined within the aqueous cytoplasm and rather than membrane associated.
Highlights
Propranolol (I) is a drug used to regulate blood pressure and anxiety levels [7,12]
As previously observed [11,18], the fluorescence spectra of propranolol vary with solvent
There is no obvious correlation of intensities at 336 and 380 nm with solvent dielectric constant and the additional band observed in water, DMF and DMSO is suggested to stem from charge transfer between the naphthalene ring and the side chain depending on strong hydrogen bond accepting character of the solvent
Summary
As a β-blocker it prevents binding of epinephrine and norepinephrine to cell surface receptors and inhibits intracellular signalling cascades. Propranolol is an amphipathic molecule that interacts with cellular membranes [18]. Recent studies [10] have shown that propranolol is rapidly taken up by live mammalian cells, but the intracellular location of accumulated propranolol was unknown. R.H. Bisby et al / Interactions of the β-blocker drug, propranolol, with detergents properties enabling it to be selectively excited in cellular environments [3,4], intracellular propranolol may be imaged during uptake into live mammalian cells. Fluorescence spectra were recorded using a Spex Fluoromax fluorimeter and absorption spectra were measured with a Perkin-Elmer Lambda-25 spectrometer. Fluorescence lifetimes with one-photon excitation were determined by time-correlated single photon counting (TCSPC) apparatus (IBH with pulsed LED excitation at 296 nm)
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