Studies are proposed to define the mechanisms by which cell-cell interactions of airway epithelium and airway smooth muscle develop during maturation. Investigations are planned to determine maturational development of 1) the modulatory functions of airway epithelium and 2) the concomitantly acquired dynamic alterations in the contraction f the myocyte of the trachea in newborn (Ngp; 7-10 day old) and adult guinea pigs (Agp). The central hypotheses of these investigations are that 1) airway responsiveness is inhibited in early postnatal life by tonic secretion of inhibitory prostaglandins (PGI2 and PGE2) by the epithelium/lamina propria, and 2) airway smooth muscle (ASM) develops increased contractile force with maturation as a result of altered rates of stability of actomyosin cross-bridge cycling in the myocyte. An in situ tracheal smooth muscle preparation that measures isometric contraction will be used to assess the relative force generation caused by contractile agonists and non-receptor-dependent stimulation (calcium ionophore) during development. Using a computerized morphometry system for calculating the content of ASM developed in preliminary studies, smooth muscle stress will be normalized using two-dimensional determinations of cross-sectional area. Preliminary data indicate that isometric force generation in tracheal smooth muscle in situ is greater in Agp than Ngp. Using a specially developed electromagnetic lever system for assessing the in vitro force-velocity characteristics of airway smooth muscle, biophysical measurements of airway shortening will be used to predict and verify the rate and number of actomyosin cross- bridges in the contractile state of Ngp and Agp. In separate studies, alterations in epithelial secretion will be measured using a specially developed in situ tracheal superfusion preparation. In preliminary studies using this preparation, concentrations of inhibitory prostaglandins have been measured by enzyme-linked immunosorbent assay (ELISA). Studies will be performed to assess the role of the epithelium in modulating smooth muscle contraction during development. Preliminary studies indicate a role for epithelial secretion in inhibiting smooth muscle contraction that diminishes with age. Studies will be performed to quantitate and verify these findings and to link mechanical changes in in situ smooth muscle contractility to maturational changes in the secretion of inhibitory prostaglandins. Development of preparations and feasibility studies for requisite techniques have been completed for all of the proposed studies. Data generated from these studies will help to elucidate the ontogeny of cell-cell interactions in the maturation of airway contractile responses.
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