The atrioventricular node (AVN) is critical to normal cardiac conduction and can also take over ventricular pacemaking should the sinoatrial node fail. The underlying basis of AVN pacemaking is incompletely understood, although it is likely to involve multiple sarcolemmal ionic currents (Hancox et al., 2003) and is influenced by intracellular calcium cycling (Ridley et al., 2008; Cheng et al., 2011). Recent evidence suggests a role for inositol trisphosphate (IP3) receptors (IP3-R) in modulating sinoatrial nodal pacemaking (Ju et al., 2011). The present study aimed to characterise the effects of modulators of IP3-R signalling on AVN cellular electrophysiology. AVN cells were isolated from adult male New Zealand White rabbits in accordance with UK Home Office legislation, as described previously (Hancox et al., 1993). Whole-cell recordings of spontaneous action potentials (APs) were made at 37oC using a standard external Tyrode’s solution and KCl-based pipette dialysate as described previously (Cheng et al., 2011). When the cell permeant IP3 analogue Bt3-Ins(145)P3/AM (10 µM) was applied, spontaneous AP rate increased from 2.86±0.20 to 4.06±0.25 Hz (Mean±SEM; n=8; P<0.01, paired t-test). This change in rate occurred without any significant change in AP upstroke velocity or AP duration at 50% repolarization (APD50). Additional experiments were performed to investigate a role for constitutively active IP3-R, using 2-aminoethoxydiphenyl borate (2-APB). Application of 10 µM 2-APB produced a 28.0±4.3% slowing of spontaneous AP rate (n=7, P<0.01); it also slowed AP upstroke velocity (by 83.4±2.7%, P<0.01) and prolonged APD50 (by 73.5±17.9%, P<0.01). Collectively, these data provide evidence that spontaneous activity of AVN cells can be modulated by IP3-R activation. Whilst the results with 2-APB are consistent with a role for constitutively active IP3-R in AVN electrophysiology, they also raise the possibility of other direct ion channel effects of 2-APB.