A method of assaying endocytosis or exocytosis comprising providing a transparent substrate with at least one cell membrane mounted thereon apposing the substrate, causing a changing in the amount of endocytosis or exocytosis at the membrane, obtaining light signals by interference light microscopy from the substrate and analysing the signals to determine the amount of exocytosis or endocytosis at the membrane. The membrane may be the cell membrane from a neuron, endocrine, exocrine, paracrine, haemopoetic, epithelial, endothelial, melancyte, sperm or egg cell or that of an organelle. The membrane may be provoked by vesicles or granules. Also claimed is an apparatus for performing the assay, comprising a transparent substrate for mounting a membrane, an interference reflection microscope and a computer to process the light signals from said microscope.
Assay method for endocytosis or exocytosis