Fig 4. Concentration response curves for the positive chronotropic effects of glucagon (A) and isoproterenol (B), in the absence (▲) and in the presence of KT-5720 (0.5 μmol/L,▼), or H-89 (3 μmol/L, ●) in the spontaneously beating rat right atria.

Results are expressed as increase in basal rate (beats min^-1). When the preparation was treated with H-89, the beating rate was reduced by 46 ± 4 beats min^-1 (n = 6), and was taken as the basal beating rate. Each point represents the mean value ± s.e.m. (vertical bars) of 4–6 experiments.