Glucose induces cytoplasmic Na+ oscillations in pancreatic beta-cells

The cytoplasmic Na+ concentration ([Na+]i) was measured in individual mouse beta-cells and islet cell aggregates using the indicator SBFI. Small oscillations of [Na+]i were occasionally observed after raising glucose from 3 to 11 mM. Distinct oscillations with a frequency of 0.29 +/- 0.02 min-1 (n = 18) and amplitudes of 7.4 +/- 0.5 mM (n = 18) were obtained when also adding the Na+ channel agonist veratridine. The oscillations were counteracted by tetrodotoxin or by lowering the glucose concentration to 3 mM. Glucose failed to induce oscillations when increasing Na+ entry by co-transport with L-glycine or raising [Na+]i by blocking the Na/K pump with ouabain. The results indicate that glucose can induce oscillations of [Na+]i in pancreatic beta-cells, although this effect is usually less obvious due to activation of an efficient Na/K pump.