Characterization of Actin and Myosin in the Developing Stomach

Abstract

During growth and development, dietary intake changes from being predominantly liquid in the newborn period to mixed solid liquid meals. These alterations in diet vary the functional demands placed on the stomach. It has been shown that, during development, smooth muscle of the stomach undergoes changes in the mechanism responsible for the contractile process. In this study, we have investigated the possibility that there are structural changes in two of the major proteins that are responsible for generation of force during smooth muscle contraction: actin and myosin. Actin and myosin were identified in newborn kittens (1 wk old) and adult gastric smooth muscle using one-dimensional SDS-PAGE. Although both the antrum and fundus of the kitten have significantly smaller total amounts of actin and myosin per mg protein than the adult, the ratio of actin to myosin is not significantly different between the age groups. Two different The changes in diet ary constitu ents during growth and development from predominantl y liquid to mixed solid liquid meals places an increasing burd en on the stomach that is required to triturate these solids and empty them from the stoma ch. The fundus or proxim al portion of the stomach is respon sibl e for the storage and empty ing of gastric food stuffs, whereas the antrum redu ces the size of ing ested solids and faci litates emptying (1). Th ere is a growing bod y of experiment al ev ide nce suggesting that functional characteristics of smoo th muscle in the sto mac h und ergo changes that parallel these alte rations in dietary mili eu. Th e frequ enc y and amplitude of contractions in the ca nine stoma ch increase during the newborn period (2). Th e in vitro force-generating capacit y of smoo th mu scle from the stomach of newborn rabbit s is less than that of adult gastri c muscl e, and this reduction in forcegeneratin g capacity did not appear to be accounted for by changes in receptor function (3,4). In addition to these quantitative differences in ability to ge nerate force, we have recentl y repo rted that isolated muscle ce lls from the antrum of the adult cat use intr acellular Ca 2 + stores that are not available for kitten antral cells (5). We observed an increase in the amount of MHC2 in the adult, which resulted 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 development. (Pediatr Res 37: 202-206, 1995) Abbreviations PMSF , phenylmethyl sulfanyl fluoride f3ME, f3-mercaptoethanol MHC , myosin heavy chain Actin and myo sin are two of the major structural proteins involved in the contractil e machinery of the cell. Th e generation of tension during muscle contraction is the result of the interaction between myos in heads and adjacent actin filaments (6). Previous studies have suggested that changes in the absolute amount and relative abundance of isoforms ...

Detection of myofibrillar proteins using a step gradient minigel with an ambiguous interface

“…Actin was identiWed by molecular weight standards and constituted the great majority of total myoWbrillar proteins in the two smooth muscle samples. Therefore, our results are consistent in that the actin content was higher than that of MHC [23,24,28], and titin and nebulin were completely absent from the smooth muscle homogenates [1,5].…”

“…3, lane 3) and urinary bladder (Fig. 3, lane 4) were similar to those in previous reports [23,24]. Actin was identiWed by molecular weight standards and constituted the great majority of total myoWbrillar proteins in the two smooth muscle samples.…”

“…Striated myoWbrils of the tibialis anterior skeletal muscle and left ventricular cardiac muscle were prepared using procedures adapted from Suzuki and coworkers [22]. Any visible adherent tissue and the mucus layer were removed from the urinary bladder and stomach, and gastric and urinary bladder smooth myoWbrils were prepared using methods similar to those described by Ayas and coworkers [23] and Malmqvist and coworkers [24], respectively. Subsequently, specimens were homogenized individually using a stainless-steel Polytron until individual myoWbrils were visible by phase contrast microscopy.…”

Neonatal mouse ileum: functional properties and protein composition of the contractile machinery

“…Consistent with previous studies with different neonatal SMs (8,9,11,12,14,31), we found that actin and myosin expression and specific active peak force elicited by KCl and carbachol at optimal length were lower compared with the adult. Specific force takes into account that the mechanical output depends on multiple factors, some of which are difficult to assess.…”

“…Although several studies addressed different aspects of the fetal and postnatal maturation of innervation, electrical activity, and global contractile activity of the GIT (5-7), only few studies addressed in some depth the properties of the downstream effector, the SM. Investigations from avian (8) and mammalian stomach (9)(10)(11), and guinea pig gallbladder (12) as well as from non-GIT organs like urinary bladder (13,14), revealed major differences between neonatal and adult tissues as regards electro-and pharmacomechanical coupling (14,15), protein composition, and functional properties of the contractile apparatus (14)(15)(16)(17). Interestingly, despite the widespread use of transgenic mouse models to investigate the contribution of individual proteins to the regulation of contraction (18)(19)(20), we are not aware of a systematic evaluation of biomechanics of the neonatal ileum coincident with its tissue architecture and protein composition of the contractile machinery.…”