Effect of interventions that affect intracellular Ca2+ handling on pacing-induced spontaneous activity in PVMS from rabbit.. Stimulation in control superfusate, (A1) after treatment with 2 umol/L ryanodine (A2), in presence of 50 umol/L CPA after wash-off of ryanodine (A3), and after wash-off of cyclopiazonic acid (CPA) (A4). B, Same protocol after treatment with 2 umol/L ryanodine (B1) and in presence of 5 mmol/L Ni2 after wash-off of ryanodine (B2). C, Same protocol after treatment with 2 umol/L ryanodine (Ry) (C1) and in presence of 50 umol/L niflumate after wash-off of ryanodine (C2). Top, stimuli; bottom, membrane potential. (Reproduced from Honjo et al Circulation 107, 1937–1943 with permission)