Differential effects of calcium channel blockers and stimulants on morphine withdrawal in vitro.

The effects of calcium channel blockers and stimulants on naloxone-precipitated morphine withdrawal in morphine-dependent ileum were evaluated in vitro. Both verapamil and diltiazem (0.01-1 microM) inhibited the naloxone-induced morphine withdrawal contractures in a concentration-dependent way. The effect of diltiazem was stereo-specific. On the other hand, the calcium channel stimulant, Bay k 8644 (0.01 microM), significantly increased the naloxone-induced contractures of morphine-dependent ileum. These results suggest a role for calcium channels in morphine withdrawal in vitro.