Abstract
Effects of 3, 4-diaminopyridine (DAP), which decreases the membrane K conductance, on the contractions of guinea-pig tracheal smooth muscle induced by histamine and prostaglandin D2 (PGD2) were investigated. Pretreatments with 5 ×10-4 and 10-3M DAP increased the exitability of histamine-induced contraction. The increment of the excitability by DAP was not suppressed by tetrodotoxin (TTX), but by nifedipine (Nif). Pretreatment with 10-3M DAP did not affect the contraction induced by PGD2. The results suggest that DAP increases the excitability of histamine-induced contraction by activating the voltage-dependent Ca channels and that PGD2 contracts tracheal smooth muscle through a mechanism different from that of histamine.
