Electrochromic behaviour of carotenoid molecules in nerve cell membranes: a resonance Raman study

It was found that, following the depolarization of cell membranes of frog sciatic nerve, the 1521 and 1156 cm-1 resonance Raman (RR) bands of carotenoids showed an increase in intensity of 20%, 15% and 4% at excitation 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 and 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 potential was obtained. Under the effect of lanthanum ions, which are known to modify the surface charge of the membrane, the intensity of the Raman bands decreased by 15%-20% (excitation, 488.0 nm). The results obtained indicate that RR spectroscopy of carotenoids can be used to monitor changes in the transmembrane potential and surface charge of nerve cell membranes.