Fig. 1
a Concentration-dependent relaxation of EI and ED PA rings induced by VIP (10−9 to 10−5 M), which was pre-contracted with 10−6 M PE. b The relationship of VIP versus contractile force in EI (filled square, n = 6) and ED rings (open square, n = 6). The response is expressed as a percentage of the active tension originally generated by 10−6 M PE. Data are expressed as mean ± SE. *P < 0.05, **P < 0.01 at each point. c Based on the data in b, the VIP-force relationship of EI rings was described with the Hill equation (y = 1/(1 + (C/IC50)h), where y is normalized force, C is VIP concentration, IC50 (10−8 M) is the VIP concentration at 50% force inhibition, and h (1) is the Hill coefficient. d Similar data fitting was done in ED rings. The IC50 is 9 × 10−8 M and h is 1.2