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Post-embedding immunogold electron microscopy shows several binding sites for cholera toxin in mouse intestinal epithelial cells, particularly in the heterochromatin of the nucleus as well as in the plasma membrane. Anti-ganglioside GM1 antibodies also bound to the nucleus, but did not interfere with the binding of toxin. 125I-labelled toxin bound specifically to a nuclear preparation from rabbit intestinal cells.

Photometric fluorescence microscopy has been used to measure intracellular pH (pHi) and free calcium concentrations [( Ca]i) in individual mouse thymocytes and 2H3 rat basophil leukaemic cells containing indicators for pH (quene 1) or calcium (quin 2). The pHi and [Ca]i measurements in individual 2H3 cells and mouse thymocytes and their responses to various stimuli were consistent with the corresponding data obtained from suspensions of these cells measured in a spectrofluorimeter. Photometric fluorescence microscopy of these indicators in individual cells provides a sensitive and fast method of following pHi and [Ca]i responses in individual cells.

A simple method for isolation and fluorescence labelling of Leydig cells (L-cells) from rat testes was developed. Lateral diffusion coefficients of both lipid and protein membrane fluorescent probes were measured by the method of fluorescence recovery after photobleaching (FRAP). Age-dependent changes in diffusibility of membrane lipids and proteins were discovered.

A method for measuring the slow rotational diffusion of lipids or lipid domains in membranes has been developed. It covers the time range from 20 microseconds-5 ms, and has a greater than 5 x 10(4) molecules of probe. The method uses acyl-substituted carbocyanine dyes as fluorescent triplet probes and a laser-microscope combination for excitation and measurement of the triplet state. Rotation rates in dimyristoylphosphatidylcholine vesicles were sensitive to the liquid-to-gel transition. Slow rotations with relaxation times of about 100 microseconds were detected at the transition temperature region.