An electrophysiological study of cultured human pituitary cells.
The electrophysiological properties of tumoral pituitary cells were studied in 4 types of human adenomas including prolactinomas, growth-hormone-secreting tumors, adrenocorticotropin-hormone-secreting adenoma and 'non-functioning' tumors. Only 9% of the cells from prolactinomas and ACTH tumors were excitable but they never elicited spontaneous action potentials. These cells did not respond to substances known to act on the hormone-releasing process (thyreoliberin, dopamine). However, 37% of the cells cultured from growth-hormone-secreting adenomas and from 'non-functioning' tumors displayed action potentials. The action potential was calcium-dependent, i.e., it was blocked by cobalt, nickel and methoxyverapamil and could be recorded in a sodium-free medium. Thyreoliberin triggered action potentials, whereas dopamine and gamma-aminobutyric acid inhibited electrical activity. These results show that human tumoral pituitary cells in culture are able to generate Ca2+-dependent action potentials. The data from growth-hormone-secreting tumors are in good agreement with the stimulus-secretion coupling concept; however, differences in the response of cells cultured from other types of human pituitary tumors suggest that each type of adenoma has specialized membrane properties.