The effects of glibenclamide and its non-sulfonylurea analogue HB 699 on the sodium content of rat pancreatic islets.

Sodium contents were determined in rat pancreatic islets using integrating flame photometry. Whereas the sodium content decreased in the presence of glucose, it increased when 0.1-100 mumol/l glibenclamide was added to a medium containing 3 mmol/l glucose. The complexity of the glibenclamide action became evident with its reversal after removal of extracellular Ca2+ and the observation that the sulfonylurea counteracted the increase of sodium obtained after removal of K+. The effects of glibenclamide were mimicked by 1 mmol/l of its non-sulfonylurea analogue HB 699 with the exception that the latter compound being without suppressive action on the sodium content in medium deprived of Ca2+. Also exposure to 1 mmol/l sulfadiazine resulted in a Ca2+-dependent increase of sodium. The results suggest a role for sodium in amplifying the secretory response to the increased entry of Ca2+ obtained with the depolarisation of the beta-cells with glibenclamide or HB 699.