Figure 5. Calcium sensitization of contractile response of various rabbit smooth muscle tissues.

Contractions for each tissue (n = 3-11) were normalized to each tissue's contractile force in response to GTPγS treatment (set as 100 %). Control contractions were measured at pCa 6.7 for the FA and AO and pCa 6.3 for the PV, TR, UB and VD. The temperature for each condition was 20 °C. Either 1 μm PDBu or 30 μm GTPγS was added. * Significant difference between the PDBu- and GTPγS-induced contractions in each smooth muscle tissue. Filled bars are Ca²⁺ alone, hatched are Ca²⁺+ PDBu and open bars are Ca²⁺+ GTPγS. The results show different PDBu-induced contractions in different smooth muscles. The GTPγS-induced contractions were 55 ± 3.8 % for AO, 64 ± 1.8 % for FA, 64 ± 1.0 % for PV, 69 ± 2.9 % for TR, 82 ± 1.7 % for UB and 70 ± 2.0 % for VD when compared to contractions induced by pCa 4.5 + GTPγS. Note that in phasic tissues, due to high phosphatase activity, the contractions at pCa 4.5 + GTPγS are still less than full maximal contraction (Kitazawa et al. 1991a).