THE STRUCTURAL CHANGES IN BOVINE ROD OUTER SEGMENTS IN THE PRESENCE OF ATP

Abstract— We have, previously, described a light-induced near infrared (700–850 nm) light scattering transient obtained in the presence of ATP from bovine rod outer segments suspensions in which the plasma but not the disk membranes were perforated (Uhl et al ., 1979a). This transient was termed the 'A' signal. To elucidate its possible origin, we have analyzed their angular and wavelength dependencies. These data have been compared with osmotically controlled (non-light) induced light scattering changes from identical control rod outer segments suspensions. It has been found that A_D (the dark light scattering signal obtained in the presence of ATP) and A_LS (the slow component of the actinic flash induced light scattering signal, A_L) can be assigned to the swelling of the disk membranes while A_Lf (the fast component of this latter signal) can be attributed to the change in refractive index of the ROS caused by the hypsochromic spectral shift of photolyzed rhodopsin. The collective disk swelling associated with A, and A_LS is consistent with the pumping of ions into the disk lumen by the action of a disk membrane bound ATPase.