Ca2+ handling of rat pancreatic β-cells exposed to ryanodine, caffeine, and glucagon

Reported species differences in the stimulus-secretion coupling of insulin release made it important to compare the Ca2+ handling of rat β-cells with that previously observed in mice. Single β-cells and small aggregates were prepared from pancreatic islets of Wistar rats, attached to cover slips and then used for measuring the cytoplasmic Ca2+ concentration ([Ca2+]i) with the ratiometric fura-2 technique. Glucose (11 mM) induced slow oscillations of [Ca2+]i similar to those seen in other species, including humans. Comparison of the oscillations in rat β-cells with those previously described in mouse revealed that there was a slightly lower frequency and an increased tendency to transformation into sustained [Ca2+]i in response to glucagon or caffeine. Ryanodine (5–20 µM) did not affect existing oscillations but sometimes restored rhythmic activity in the presence of caffeine. Stimulation with glucose resulted not only in oscillations but also in transients of [Ca2+]i sometimes appearing in synchrony in adjacent β-cells and disappearing after the addition of 200 nM thapsigargin 20 mM caffeine. The frequency of transients recorded in a medium containing glucagon and methoxyverapamil was higher than seen under similar conditions in mouse β-cells. Although exhibiting some differences compared with mouse β-cells, rat β-cells also have an intrinsic ability to oscillate and to generate the transients of [Ca2+]i that are supposed to synchronize the rhythmicity of the islets in the pancreas.