Further studies on absorption changes arising in dye-stained nerves during excitation

Abstract

Changes in light absorption during nerve excitation (absorption responses) were detected from the crab leg nerve, the rabbit vagus, and the rat superior cervical ganglion (SCG) stained with a merocyanine-rhodanine. Dependences of the responses on the wavelength and polarization of the incident light (absorption spectra) showed characteristic features with the respective nerves. In the crab nerve, the pattern of response spectra was precisely analyzed based on the previously proposed scheme, which included the shift of absorption bands and the statistical reorientation of absorption oscillators of the dye molecules in the membrane matrix during nerve excitation. Different patterns of the response spectra between the crab nerve and the rabbit vagus suggested that distinct physicochemical environments of the dye occurred in these two classes of membranes. On the other hand, the characteristic pattern that arose in the rat SCG was explained by its morphological form, that is, unlike those in a bundle of axons, the membrane elements in the ganglion were randomly oriented with respect to the direction of the light polarization.

Charge-shift probes of membrane potential. Characterization of aminostyrylpyridinium dyes on the squid giant axon

“…In addition, there is the possibility of a more uniform set of responses with electrochromic probes for different membrane preparations. Certain other mechanisms require a delicate energetic balance between two or more chemical states of the probe so that the equilibrium populations may be appreciably altered by the potential; this delicate balance may not be conserved over a range of membrane preparations (Ross and Reichardt, 1979;Warashina, 1980;Boyle et al, 1983). Under the assumption that the orientation of bound probes can be defined by the placement of hydrophilic and hydrophobic side chains rather than specific interactions with membrane proteins, an electrochromic response will not be especially sensitive to the particular membrane environment.…”