Fig 1. Effect of glucagon and isoproterenol on spontaneous beating rate and basal force of contraction in rat right atria.

Representative traces showing that isoproterenol increases atrial contractility (A). In contrast, glucagon is virtually devoid of inotropic effect in a right atria which responds to Ca²⁺ (B). Cumulative concentration-response curves for the chronotropic (C) and inotropic (D) effects of glucagon (■) and isoproterenol (▲). Chronotropic and inotropic responses are expressed as increase in basal rate (278 ± 7 beats min^-1) and contractility (3.3 ± 0.4 mN), respectively. Each point represents the mean value ± s.e.m. (vertical bars) of 5–12 experiments.