Pancreatic beta-cells have an intrinsic oscillatory Ca2+ activity supposed to be synchronized among the islets by cytoplasmic Ca2+ transients elicited by nonadrenergic, noncholinergic (NANC) neurons. To improve the understanding of this process, the cytoplasmic Ca2+ concentration ([Ca2+](i)) was measured in two insulin-releasing cell lines using dual wavelength microfluorometry and the indicator fura-2. INS-1 cells but not RINm5F cells were found to generate transients of [Ca2+](i) in the presence of the Ca2+ channel blocker methoxyverapamil. These transients differed from those occurring in native beta-cells persisting in the presence of thapsigargin or during prolonged exposure to ATP. Moreover, the [Ca2+](i) transients were poorly synchronized whether or not the INS-1 cells had physical contact. If appearing in native beta-cells, the type of [Ca2+](i) transients now observed may interfere with the coordination of the beta-cell rhythmicity evoked by NANC neurons. (C) 2002 Elsevier Science (USA). All rights reserved.