CHARACTERIZATION OF ACTIN AND MYOSIN IN THE DEVELOPING STOMACH

During growth and development, dietary intake changes from being predo minantly liquid in the newborn period to mixed solid liquid meals. The se alterations in diet vary the functional demands placed on the stoma ch. It has been shown that, during development, smooth muscle of the s tomach undergoes changes in the mechanism responsible for the contract ile process. In this study, we have investigated the possibility that there are structural changes in two of the major proteins that are res ponsible for generation of force during smooth muscle contraction: act in and myosin. Actin and myosin were identified in newborn kittens (1 wk old) and adult gastric smooth muscle using one-dimensional SDS-PACE . Although both the antrum and fundus of the kitten have significantly smaller total amounts of actin and myosin per mg protein than the adu lt, the ratio of actin to myosin is not significantly different betwee n the age groups. Two different myosin heavy chain (MHC) isoforms, MHC 1 (205 kD) and MHC2 (200 kD), were identified in all tissues. The rela tive amount of MHC1 remained constant during maturation of the stomach . We observed an increase in the amount of MHC2 in the adult, which re sulted in a decreased ratio of MHC1 to MHC2 in the adult. We postulate that the decreased quantity of actin and myosin in the kitten stomach and the observed changes in the ratio of the MHC isoforms are related to changes in the gastric motor that occur during growth and developm ent.