Glucagon amplifies tetrodotoxin-resistant Na+ oscillations in glucose-stimulated pancreatic beta-cells.

The cytoplasmic concentration of Na + ([Na + ] i ) was measured in individual mouse β-cells with dual-wavelength microfluorometry using the indicator SBFI. The addition of 10 nM glucagon to a medium containing 11 mM glucose and 1.3 mM Ca 2+ resulted in a 24% increase of [Na + ] i often associated with superimposed oscillations. When replacing Ca ith 5 mM Sr 2+ , the presence of glucagon resulted in an increase of the amplitude of the [Na + ] i oscillations with decrease of their frequency. Similar effects as with glucagon were obtained with 1 mM 8-Br-cAMP or 5 μM of the Ca 2+ channel agonist BAY K8644. The glucose-induced oscillations of [Na + ] i were resistant to 3 μM tetrodotoxin and disappeared after addition of 100 nM clonidine, 10 μM methoxyverapamil or 400 μM diazoxide. Studies of cell aggregates revealed the existence of well synchronized [Na + ] i oscillations similar to those in individual β-cells. The results provide evidence for tetrodotoxin-resistant [Na + ] i rhythmicity in glucose-stimulated pancreatic β-cells subject to regulation with cAMP.