Effect of dantrolene sodium in isolated guinea-pig trachea

The effect of dantrolene sodium (3 μM-0.3 mM) on the spontaneous tone and responses to various contractile agonists was studied in isolated guinea-pig trachea. Dantrolene produced a concentration-related inhibition of the spontaneous tracheal tone, reaching a value of 94.8 ± 4.8% of the relaxation induced by caffeine 10 mM. Removal of the epithelium did not affect the dantrolene-induced relaxation. Dantrolene did not alter the concentration-response curve for KCl and produced only small displacements of the concentration-response curves for CaCl 2, acetylcholine and histamine, without affecting their maximal effects. Dantrolene dose relatedly inhibited the contraction induced by caffeine (1 mM) in Krebs solution containing indomethacin (2.8 μM) at 20°C. The spasm induced by caffeine in Ca 2+-free Krebs solution (20°C, indomethacin 2.8 μM) was slightly depressed by dantrolene. Dantrolene did not depress the Ca 2+ (1 μM)-induced contraction in skinned trachea. These results suggest that besides a possible intracellular site of action, the mechanism of the inhibitory effect of dantrolene in guinea-pig trachea may be related to interference with Ca 2+ entry through pathways not susceptible to calcium channel blockers.