Fig. 2. Concentration-dependent effects of bupivacaine or ropivacaine on peak systolic [Ca2+]iand tension. ( A ) Effects of bupivacaine. 0 μm = no bupivacaine. *P < 0.05 for [Ca2+]i: 0 μm versus 30 μm, 0 μm versus 100 μm, 10 μm versus 100 μm, 30 μm versus 100 μm; *P < 0.05 for tension: 0 μm versus 10 μm, 0 μm versus 30 μm, 0 μm versus 100 μm, 10 μm versus 30 μm, 10 μm versus 100 μm, 30 μm versus 100 μm; n = 8. ( B ) Effects of ropivacaine. 0 μm = no ropivacaine. *P < 0.05 for [Ca2+]i: 0 μm versus 30 μm, 0 μm versus 100 μm, 10 μm versus 100 μm; *P < 0.05 for tension: 0 μm versus 30 μm, 0 μm versus 100 μm, 10 μm versus 100 μm, 30 μm versus 100 μm; n = 8. ( C ) Comparison of the inhibitory effects of bupivacaine and ropivacaine on peak systolic [Ca2+]i. Data are taken from ( A ) and ( B ) and shown as percentage changes in [Ca2+]i(normalized with respect to control). BUP = bupivacaine; ROP = ropivacaine. P < 0.05 compared with the data for ROP. ( D ) Same as in ( C ) for peak systolic tension. *P < 0.05 compared with the data for ROP. ( E ) Relations between the reduction of tension and that of [Ca2+]iwith bupivacaine and ropivacaine. Data obtained in ( C ) and ( D ) are used. BUP (circles) , Y = 1.31X + 5.95 (R = 0.94, P < 0.01); ROP (triangles) , Y = 0.99 X + 6.70 (R = 0.89, P < 0.01). The slopes for BUP and ROP are significantly different ( P < 0.05) .