Enhancement of phenoxybenzamine-induced irreversible blockade by organic Ca antagonists

Organic Ca antagonists such as D600, diltiazem and nicardipine enhanced the irreversible blockade by phenoxybenzamine (POB) of the histamine response in guinea pig taenia caecum. The isotonic contractile response of the muscle was tested after incubation with POB (5 X 10(-6) M, 10 min) with or without an organic Ca antagonist. The blockade by POB was greater in muscle treated with an organic Ca antagonist and the effect lasted for more than 7 h.