Calcium-dependent ultrasound stimulation of secretory events from pancreatic beta cells

BACKGROUND: Our previous studies have indicated that ultrasound can stimulate the release of insulin from pancreatic beta cells, providing a potential novel treatment for type 2 diabetes. The purpose of this study was to explore the temporal dynamics and Ca(2+)-dependency of ultrasound-stimulated secretory events from dopamine-loaded pancreatic beta cells in an in vitro setup. METHODS: Carbon fiber amperometry was used to detect secretion from INS-1832/13 beta cells in real time. The levels of released insulin were also measured in response to ultrasound treatment using insulin-specific ELISA kit. Beta cells were exposed to continuous wave 800 kHz ultrasound at intensities of 0.1 W/cm(2), 0.5 W/cm(2) and 1 W/cm(2) for several seconds. Cell viability tests were done with trypan blue dye exclusion test and MTT analysis. RESULTS: Carbon fiber amperometry experiments showed that application of 800 kHz ultrasound at intensities of 0.5 and 1 W/cm(2) was capable of stimulating secretory events for durations lasting as long as the duration of the stimulus. Furthermore, the amplitude of the detected peaks was reduced by 64% (p < 0.01) when extracellular Ca(2+) was chelated with 10 mM EGTA in cells exposed to ultrasound intensity of 0.5 W/cm(2). Measurements of released insulin in response to ultrasound stimulation showed complete inhibition of insulin secretion by chelating extracellular Ca(2+) with 10 mM EGTA (p < 0.01). Viability studies showed that 800 kHz, 0.5 W/cm(2) ultrasound did not cause any significant effects on viability and metabolic activity in cells exposed to ultrasound as compared to sham-treated cells. CONCLUSIONS: Our results demonstrated that application of ultrasound was capable of stimulating the release of insulin from pancreatic beta cells in a safe, controlled and Ca(2+)-dependent manner.