Stimulation of secretion from bovine adrenal chromaffin cells by microsecond bursts of therapeutic levels of ultrasound

1. In this study the secretory response of individual bovine adrenal chromaffin cells was monitored using amperometric carbon-fibre microelectrodes. Cells were stimulated to secrete by exposure to 20-100 μs long tonehursts of ultrasonnd (2-4 x 10⁵ Pa; peak pressure at 1 MHz). 2. Three types of secretory responses were observed: an almost instantaneous response, a delayed release of catecholamines, or a series of 'burst-like' secretory bouts. 3. Fura-2 measurements of intracellular Ca²⁺ concentrations showed that the release of catecholamines was accompanied by an increase in the intracellular Ca²⁺ concentration. In the absence of extracellular Ca²⁺, secretory responses were not evoked showing that Ca²⁺ entry was necessary to elicit catecholamine release.