The dependence of airway smooth muscle on extracellular Ca2+ for contraction is influenced by the presence of cartilage.

Isolated guinea-pig and rabbit airway smooth muscle preparations lacking cartilage are less able to contract, in response to methacholine, histamine and K+, in the absence of extracellular Ca2+ than cartilage-containing preparations removed from the same animal. Cartilage apparently provides utilizable Ca2+ for contraction of airway smooth muscle. The presence of cartilage, therefore, affects the apparent dependence of the isolated smooth muscle on extracellular Ca2+ for contraction.