title: Weaving hypothesis of cardiomyocyte sarcomeres: discovery of periodic broadening and narrowing of intercalated disk during volume-load change.
abstract: To investigate how cardiomyocytes change their length, echocardiographic and morphological studies were performed on rabbit hearts that were subjected to volume overload, overload removal, and repeated cycles of overload and overload removal. These conditions were created by arterio-venous fistula between the carotid artery and jugular vein, closure of the fistula, and cycles of repeatedly forming and closing fistula, respectively. After overload, hearts dilated and myocytes elongated. Intercalated disks repeatedly broadened and narrowed with a 2-day cycle, which continued for 8 weeks in many animals. The cycle consisted of shifts between five modes characterized by two interdigitation elongation-and-shortenings as follows: (I) flat with short ( approximately 1/4 to approximately 1/3 sarcomere long) interdigitations; (II) flat with long (one sarcomere long) interdigitations; (III) grooved with short interdigitations; (IV) grooved with long interdigitations; (V) flat with short interdigitations intermingled by sporadic long interdigitations; and return to (I). After overload removal, hearts contracted and myocytes shortened with similar 2-day broadening and narrowing cycle of intercalated disks, in which the five modes were reversed. Repeated overload and overload removal resulted in the repetition of myocyte elongation and shortening. We hypothesize that a single elongation-and-shortening event creates or disposes one sarcomere layer, and the two consecutive elongation-and-shortenings occur complementarily to each other so that the disks return to their original state after each cycle. Our hypothesis predicts that intercalated disks weave and unravel one sarcomere per myocyte per day.
authors.affiliation: Graduate School of Medicine, Akita University, Akita 010-8543 Japan. .
authors.forename: Makoto
authors.initials: M
authors.lastname: Yoshida
authors.forename: Eiketsu
authors.initials: E
authors.lastname: Sho
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nanjo
authors.forename: Masato
authors.initials: M
authors.lastname: Takahashi
authors.forename: Mikio
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Kouiti
authors.initials: K
authors.lastname: Kawamura
authors.forename: Makiko
authors.initials: M
authors.lastname: Honma
authors.forename: Masayo
authors.initials: M
authors.lastname: Komatsu
authors.forename: Akihiro
authors.initials: A
authors.lastname: Sugita
authors.forename: Misa
authors.initials: M
authors.lastname: Yamauchi
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hosoi
authors.forename: Yukinobu
authors.initials: Y
authors.lastname: Ito
authors.forename: Hirotake
authors.initials: H
authors.lastname: Masuda
mesh_terms: D000818:Animals; D002306:Cardiac Volume / Q000502:physiology*; D048429:Cell Size; D004452:Echocardiography / Q000379:methods; D006321:Heart / Q000502:physiology; D007365:Intercellular Junctions / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure; D008297:Male; D008954:Models, Biological; D009206:Myocardium / Q000648:ultrastructure; D032383:Myocytes, Cardiac / Q000166:cytology / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure*; D010507:Periodicity; D011817:Rabbits; D012518:Sarcomeres / Q000000981:diagnostic imaging / Q000502:physiology* / Q000648:ultrastructure