The isolation of stable cattle rod outer segments with an intact plasma membrane.

A procedure is described to purify and stabilize cattle rod outer segments with an intact plasma membrane. Three criteria are applied to assess the integrity of the latter. Upon photolysis in these rod outer segments: (1) exogenous ATP cannot phosphorylate rhodopsin located in the disk membrane. (2) Endogenous cofactors (NADPH, NADPH-regenerating system) are still available in the rod cytosol and consequently retinol is the final photoproduct of photolysis of rhodopsin. (3) The rod cytosol can maintain a pH different from that of the medium, since the later stages of rhodopsin photolysis are independent of the medium pH. The stability and homogeneity of the preparation appear to be much better than those of freshly isolated frog rod outer segments, which have been used most frequently so far for experiments on the physiology of rod outer segments. In addition, these cattle rod outer segments remain intact during various manipulations and therefore considerably extend the experimental possibilities when intact rod outer segments are required.