Age-related alterations in sensitivity of muscarinic and serotonergic responses of guinea pig trachea to removal of extracellular Ca2+.

Contractile responses to carbamylcholine and 5-hydroxytryptamine (5-HT) in the presence and absence of extracellular Ca2+ 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 Ca2+. However, removal of extracellular Ca2+ 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 Ca2+ as compared to mature animals, and may be related to an age-dependent maturation of sarcoplasmic reticulum function in smooth muscle.