Abstract
Acetylcholine (ACh)-induced contractions of dog tracheal smooth muscles were studied in order to determine the sources of Ca++ for these contractions become diminished with time at all drug doses and experiments with 45Ca indicate that this phenomenon is related to the efflux of Ca++ from the muscle. This efflux of Ca++ consists of two components, a loosely bound and a tightly bound Ca++ source, and is dependent upon the dose of drug. At low doses of ACh (less than 10(-6) M) loosely bound Ca++ plays a greater role and tightly bound Ca++ a lesser role than at higher drug doses. Verapamil, a blocker of depolarization-dependent Ca++ influx, inhibits ACh contractions at low drug doses but has no effect at higher doses. These results indicate that the sources of Ca++ for ACh contractions of the trachea are dependent upon the drug dose. At low doses of ACh (less than 10(-6) M ACh) depolarization-dependent Ca++ influx is involved in musch of the contraction. At the higher drug doses a tightly bound Ca++ source and a depolarization-independent, loosely bound Ca++ source account for the contractions.
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|