A, typical experiment showing the lack of effect of L-NMMA (1 mM) in the presence of external L-arginine (L-arg) (5 mM). Stimulation protocol as in Fig. 1A, single traces at the times indicated by the arrows in A, during L-arginine treatment (1) and in the presence of both L-arginine and L-NMMA (2). C, time course of ICa in a representative cell internally perfused with 5 mM L-arginine and then stimulated with 1 mM L-NMMA. L-arginine was applied directly in the perfusion pipette from the beginning and L-NMMA stimulation started after a few minutes. D, single traces of ICa recorded at the time indicated by the arrows in C, during L-arginine perfusion alone (1) and after L-NMMA application (2). E, bar graph showing the absence of significant effect of L-NMMA (1 mM) on basal ICa in the presence of external (ext) (***P < 0.001 vs. L-NMMA on basal ICa) and internal (int) (***P < 0.001 vs. L-NMMA on basal ICa) L-arginine (5 mM).