Fig. 1.

Acute exposure to inorganic lead ions has a negative inotropic effect on isolated guinea-pig hearts. a Recordings of tension at the base of the papillary muscle versus time after application of different concentrations of extracellular Pb²⁺. The Pb²⁺ was added to the extracelular perfusion solution (1.8 mM Tyrode’s solution). Application of 20 μM Pb²⁺ causes appearance of contractions at various times with varying amplitudes. The overall average amplitude diminishes with increasing extracelular lead. b Dose–response curve of force amplitude of contraction versus extracelular Pb²⁺ concentration. There is also a monotonic decrease of force, measured as tension, with increasing Pb²⁺ concentrations. Symbols represent average values with standard error bars (n = 6). The solid line corresponds to the best fit of a Hill equation of the type F = Fo + AF. D^h / (IC50^h + D^h), where h is the hill coefficient, IC50 is the half-dose for the observed effect, Fo is the minimal force, AF is the maximum observed variation in force (force initially at dose 0−Fo at maximal dose), F is force amplitude and D is the concentration of extracellular lead ions