Fig. 9. The relationship between extracellular Ca²⁺ and contractile force. Twitch force is expressed as a percentage of the difference between maximum force development and baseline force at 1.5 mmol l^-1 Ca²⁺ for (A) male and female ventricle strips receiving 5 mmol l^-1 glucose; (B) female ventricle strips, glucose vs glucose-free and (C) male ventricle strips, glucose vs glucose-free. In the presence of glucose, the EC₅₀ for Ca²⁺-dependent force production was lower in females than males (P<0.01). Compared with tissue receiving glucose, glucose-free ventricle strips from both sexes were less sensitive to Ca²⁺ (P<0.05) but sex differences were not evident. Values are means ± s.e.m. (N=8-9 strips per curve).