Novel preparation for studying excitation–secretion coupling in the isolated single cell

Cellular mechanisms of secretion in exocrine and endocrine glands are technically difficult to study. We present here a model which offers fundamental advantages for studying excitation–secretion coupling at the level of the isolated single cell. The salivary gland of the leech Haementeria ghilianii possesses a unique combination of unusual properties which greatly facilitate research in this area. Its cells are exceptionally large (up to 1 mm in diameter), clearly visible and easy to penetrate with microelectrodes. They do not form a homogeneous population but consist of five distinct histochemical types, secreting a number of identified products such as the fibrinolytic enzyme hementin (for which there is a sensitive assay). The cells generate overshooting calcium-dependent action potentials up to 90 mV in amplitude and with a duration of 200–1,000 ms. One of their most useful and unusual features is a lack of electrical coupling which means that individual cells can be studied in an intact gland without interference from neighbouring cells.