The Fetal Mouse Heart in Organ Culture: Maintenance of the Differentiated State

This chapter describes the fetal mouse heart in organ culture. Myocardial metabolism, structure, and function have been studied in many in vitro preparations, including isolated perfused hearts, papillary muscle strips, and heart cells in monolayer culture. Some of the morphological, functional, and biochemical measurements that have been made on hearts weighing only 2–5 mg are presented. The nature of the atrial–ventricular activation sequence and frequency of contraction of cultured hearts can be identified simply by visual inspection using a light microscope. The results suggest that different classes of proteins accumulate at different rates during development. The specific activity of MM-CPK that increases more than two orders of magnitude during the last trimester of development emphasizes the dynamic nature of developing tissue and thus the need for designing experimental protocols using hearts of the same size. Deprivation of oxygen and glucose for periods longer than 3 hours resulted in substantial irreversible injury. Such long-term deprivation resulted in 75% reduction in total purine nucleotide content and 40% loss of purine nucleosides and bases from hearts into the culture medium.