The rat anococcygeus muscle is densely innervated by sympathetic nerves. When electrically stimulated, these nerves release noradrenaline, producing a biphasic excitatory junction potential (EJP) and contraction (Creed et al., 1975). The first component of the EJP is a depolarisation, thought to be produced by the effect of increased free cytosolic [Ca²⁺] on Ca²⁺-activated Cl^– channels (Bramich & Hirst, 1999). Noradrenergic transmission in intact tissue produces intracellular Ca²⁺ transients in individual smooth muscle cells in the form of waves and synchronised whole cell flashes (Amos et al., 2005). However, the relationship between the EJP and the different Ca²⁺ transients, and the extent to which local Ca²⁺ increase affects the local membrane potential, is unknown. To explore this relationship, the anococcygeus was isolated from male Wistar rats (200 – 400 g) and smooth muscle membrane potentials were measured using sharp microelectrodes, while intracellular Ca²⁺ was monitored simultaneously using a confocal microscope and the Ca²⁺ indicator Oregon Green 488 BAPTA-1. The indicator was delivered to individual smooth muscle cells through a microelectrode as a membrane impermeable salt. Dye coupling between adjacent smooth muscle cells was not observed with this method. In 9 cells (from 5 preparations) studied with this method, EJPs could be elicited with a distinct first component, but only 6 of these showed Ca²⁺ waves (trains of 1 – 6 pulses, 1 – 10 Hz, 0.2 ms pulse width). Where waves initiated within the field of view, the initiation times of the rise in Ca2+ and the first component of depolarisation were well correlated (Spearman’s rank correlation coefficient +0.717, P < 0.01). There was however no correlation between the peak amplitude of the first component of the EJP and that of the point of initiation of the Ca²⁺ increase. The threshold (frequency of stimulation, number of pulses in a train) for generating the first component and waves varied; varying the stimulation frequency or number of pulses, 6 of these 9 cells exhibited first components of depolarisation at thresholds where waves were not observed, while 2 displayed waves without the first component and in 1 cell, waves and first components appeared at the same threshold. These results suggest that the first component of the EJP in the intact organ is not the result of local Ca²⁺ waves within one smooth muscle cell. Since the input resistance of anococcygeus muscle is only 18 – 29 MΩ (Creed et al., 1975), the EJP is instead likely to reflect Ca²⁺ and electrical events in a population of electrically-coupled smooth muscle cells.