Abstract
Contractile responses to carbamylcholine and 5-hydroxytryptamine (5-HT) in the presence and absence of extracellular Ca 2+ were compared in tracheal rings from 3–4-week-old and 7–8-week-old guinea pigs. Contraction to carbamylcholine and 5-HT did not differ in potency or maximal response between age groups in the presence of extracellular Ca 2+. However, removal of extracellular Ca 2+ inhibited maximal contraction mediated by both agonists to a greater extent in younger versus older guinea pigs. These data suggest that carbamylcholine- and 5-HT-induced contraction of guinea pig trachea from younger animals is more dependent on extracellular Ca 2+ as compared to mature animals, and may be related to an age-dependent maturation of sarcoplasmic reticulum function in smooth muscle.
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