Fig. 6.

Comparison of inotropic responses to carbachol in left atria isolated from wild-type (WT), M₂KO, M₃KO, and M₂/M₃KO mice. A, after establishing reproducible EFS-induced atrial contractions, carbachol (10 nM–100 μM) was applied noncumulatively at 30-min intervals, and concentration-response relationships were constructed. The asterisk (*) indicates significant increase compared with the values before application of carbachol. B, time courses of inotropic responses to carbachol in left atria isolated from WT, M₂KO, M₃KO, and M₂/M₃KO mice. After stable EFS-induced contractions had been obtained, carbachol (30 μM) was applied to the organ bath, and inotropic responses were observed for 20 min. Ordinate, relative amplitude of EFS-induced contraction expressed as a percentage of the amplitude just before application of carbachol. Abscissa, concentration of carbachol (log M) (A) and incubation time with 30 μM carbachol (min) (B). Values are means and S.E.M. of five to seven experiments. B, the asterisk (*) indicates significantly different compared with WT values.