Meeting Abstract

P2.142  Monday, Jan. 5  Development of the guinea pig (Cavia porcellus) diaphragm WOO, H.**; WEIGAND, K.L.; DEAROLF, J.L.; Hendrix College, Conway, AR woohh@hendrix.edu

Neonatal mammals, because of their increased metabolic rates, breathe faster than their adult counterparts. For example, neonatal guinea pigs take 123 breaths per minute, a rate 40% higher than the adult ventilatory rate (87 breaths/minute). These increased breathing rates suggest that neonatal ventilatory muscles have greater proportions of fast-twitch fibers than adult muscles. But, to support neonatal breathing rates, the fast-twitch fibers also need to have adult contractile abilities. To test these hypotheses, the fiber-type profiles and myosin heavy chain (MHC) expression patterns of neonatal and adult guinea pig diaphragms were determined. We expect that the muscles of neonates will contain 40% more fast-twitch fibers than the diaphragms of adults, based on the difference in their ventilatory rates. To have adult contractile abilities, neonatal muscles will also express only adult MHCs. Muscle samples were collected from 1-day-old neonatal and adult (49- and 59-days gestation) guinea pigs and prepared for histochemistry or SDS-polyacrylamide gel electrophoresis. The neonatal diaphragm contained 87.5% ( 0.67) fast-twitch fibers, approximately 40% more fast-twitch fibers than found in the adult muscle (63.7% 2.5). These results support the hypothesis that neonatal breathing muscles contain greater proportions of fast-twitch fibers than adult muscles. They also fit our expectation for the neonatal guinea pig diaphragm. Our findings suggest that the differences in ventilatory rates between neonatal mammals and their adult counterparts can be used to predict the fiber-type profiles of neonatal breathing muscles, if the adult profile is known. Preliminary analyses of the myosin gels show only adult MHCs being expressed in the neonatal diaphragms, indicating that these muscles have adult contractile abilities.