The Contraction Mechanisms for Norepinephrine in Single Cells Prepared from Tracheal Smooth Muscles of Guinea Pig of Different Ages.

Abstract

-Single cells were prepared from guinea pig tracheal smooth muscle and used in an experiment on the contraction mechanisms for norepinephrine and a study on the change of a2-adrenoceptors with age. Specific bindings of [3HIp-aminocloni dine to the single cells from the tracheal smooth muscles of 6 and 40-week-old guinea pigs were saturable and analyzed by Scatchard plot. The maximum number of [3H]p aminoclonidine binding sites was larger in the preparation from 40-week-old guinea pigs than that from 6-week-old animals, while its dissociation constant did not change with age. The amount of prostaglandin F2a released from the single cells was increased by norepinephrine, not affected by phenylephrine, and reduced by an a2-antagonist such as yohimbine. The amount released by norepinephrine was significantly larger in the preparation from 6-week-old guinea pigs than that from 40-week-old animals. These results suggest that the age-related decrease in the potency of norepinephrine is due to reduction in the amount of excitable prostaglandin F2a released by the drug, but not to a change in the total amount of a 2-adrenoceptors or the dissociation con stant of the drug with respect to these adrenoceptors. Furthermore, a 2-adrenoceptors in the tracheal smooth muscle cell play an important role in the release of prostaglan din F2a and the production of contractile responses of these muscles.Takagi et al. first reported in 1967 that guinea pig tracheal smooth muscle contains both a-adrenoceptors and ,Q2-adrenoceptors (1). Takayanagi et al. (2, 3) recently reported the existence of a 2-adrenoceptors in the guinea pig trachea with which norepinephrine interacts and releases excitatory prostaglan dins, mainly prostaglandin F2a , to contract tracheal muscles. Norepinephrine potency re portedly decreases with age (4). In membrane fractions derived from the tracheal muscles of 6 and 40-week-old guinea pigs, the capacity of maximum binding sites of [3Hlp-amino clonidine was greater in the older animals, whereas the dissociation constant was un changed by age. The amount of prostaglandin F2a released by norepinephrine and the con tractile response to it decreased with age. Takayanagi et al. (1991) concluded from these results that the age-related decrease in the potency of norephinephrine is due to a reduc tion in the amount of excitable prostaglandin F2a released by norepinephrine and a reduc tion in the contractile response to prostaglan din F2a , but not to a change in the character istics of a2-adrenoceptors (4).To clarify the effects of aging on the con traction mechanism(s) for norepinephrine in

Age-Related Changes in Alpha-Adrenoceptor Mediated Blood Pressure in the Rat: Relationship between the Potency for Phenylephrine and the Maximum Number of Binding Sites

“…Single smooth muscle cells from rat thoracic aorta were prepared by the method of Momose and Gomi [12] modified by Takayanagi et al [13] and Satoh and Takayanagi [14], Male Wistar rats (6, 10 and 40 weeks old) were killed and the thoracic aorta quickly re moved and suspended in an incubation medium made up ofthe following: 137 mmol/l NaCI, 2.7 mmol/l KC1. 1.0 mmol/l MgCI2.…”

Arachidonic acid metabolites and glucocorticoid regulatory mechanism in cultured porcine tracheal smooth muscle cells

“…The arachidonic acid metabolites released from airway smooth muscle cells in culture have not been characterized. Previous reports have demonstrated the release of prostaglandin E from isolated guinea pig trachea smooth muscles [13] following stimulation with histamine and PGF2~ from single cells prepared from tracheal smooth muscles [33].…”

Identification and Characterization of the α2d-Adrenoceptor Subtype in Single Cells Prepared from Guinea Pig Tracheal Smooth Muscles

“…Single smooth muscle cells from guinea pig trachea were prepared by the method of Momose and Gomi (7), with some modifications, which was described in the previous report (8). The [3H]p-aminoclonidine bind ing assay was performed with these single cells.…”