The effects of verapamil on leukotriene D4 (LTD4)‐ and KCl‐induced contractions and 45Ca‐uptake were examined in guinea‐pig isolated tracheal smooth muscle.
Both LTD4 (0.1 to 200 nmol l−1) and KCl (8 to 125 mmol l−1) produced concentration‐dependent increases in tension in the tracheal preparations.
Verapamil (1 μmol l−1) inhibited the tension responses induced by both LTD4 and KCl.
LTD4 failed to increase the lanthanum‐resistant Ca content of tracheal smooth muscle at either low (EC25; 3 nmol l−1) or high (EC90; 50 nmol l−1) concentrations. Verapamil did not modify this result.
KCl (90 mmol l−1) increased the lanthanum‐resistant Ca content of the smooth muscle by approximately 60% over basal levels. This effect was completely inhibited by verapamil (1 μmol l1).
It is concluded that in this tissue, LTD4 utilizes principally an intracellular source of Ca2+ to initiate contraction whereas KCl is dependent upon the uptake of Ca2+ from the extracellular compartment. It is suggested that the inhibitory effects of verapamil may reflect an intracellular mechanism of action directed against Ca2+ release initiated by LTD4.