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Liposomes have been prepared with a phospholipid ratio and a cholesterol content similar to that of the outer segments of rod photoreceptor cells. Studies were made of the appearance, electrophoretic mobility and sodium leakage rates of the liposomes, with and without the inclusion of protein (albumin, myoglobin, ribonuclease, lysozyme, proteolipid or opsin). The findings indicate that although the appearance and properties of these liposomes closely resemble those of other liposomes reported in the literature, the liposomes become markedly changed in appearance, electrophoretic mobility and sodium permeability by the addition of opsin. These data emphasize the hydrophobic nature of the opsin-lipid interaction and suggest an ability of opsin to alter the ion leakage properties of a rod outer segment membrane.

Tritiated thymidine [(3H]thymidine) autoradiographic techniques have been used to define birthdates for cells in a variety of animals. In an effort to include [3H]thymidine experiments in our ongoing studies of visual system development, we have used an intrauterine injection procedure that affords [3H]thymidine labeling of dividing nerve cells in the cat. This report contains a detailed description of the injection procedures used, as well as the results of experiments undertaken to define the period of time during which the exogenous [3H]thymidine introduced by such injections remains available for uptake.

Quantities of adenosine 3′,5′-cyclic monophosphate were measured in rabbit corneal endothelial cells taken from fresh tissue and tissue culture. Higher levels of both nucleotides were observed when the cells were initially frozen in liquid nitrogen compared with those that were not. Adenosine 3′,5′-cyclic monophosphate was 14 times lower in the primary cultures compared to the fresh tissues while subcultures were about two-thirds that of the fresh tissue amount. Guanosine 3′,5′-cyclic monophosphate was four times higher in the primary cultures compared to the fresh tissue while subcultures were about two-thirds that of the fresh tissue amount. It is emphasized that the ratios of adenosine 3′,5′-cyclic monophosphate to guanosine 3′,5′-cyclic monophosphate were similarly high in both fresh tissue and subcultured cells approaching confluency, but quite low in primary outgrowths.