ELECTROCHROMIC BEHAVIOR OF CAROTENOID MOLECULES IN NERVE-CELL MEMBRANES - A RESONANCE RAMAN-STUDY

It was found that, following the depolarization of cell membranes of f rog sciatic nerve, the 1521 and 1156 cm-1 resonance Raman (RR) bands o f carotenoids showed an increase in intensity of 20%, 15% and 4% at ex citation wavelengths of 488, 496.5 and 514.5 nm respectively. None of the bands revealed any change with excitation at 441.6, 457.9, 472.7 a nd 476.5 nm. These results can be explained by an electrochromic shift of the excitation profile of the RR bands by about 0.5 nm to the red. A dependence of the 1521 cm-1 band intensity on transmembrane potenti al was obtained. Under the effect of lanthanum ions, which are known t o modify the surface charge of the membrane, the intensity of the Rama n bands decreased by 15%-20% (excitation, 488.0 nm). The results obtai ned indicate that RR spectroscopy of carotenoids can be used to monito r changes in the transmembrane potential and surface charge of nerve c ell membranes.