title: Cytochalasin D reduces Ca2+ sensitivity and maximum tension via interactions with myofilaments in skinned rat cardiac myocytes.
abstract: The F-actin disrupter cytochalasin D depresses cardiac contractility, an effect previously ascribed to the interaction of cytochalasin D with cytoskeletal actin. We have investigated the possibility that this negative inotropic effect is due to the interaction of cytochalasin D with sarcomeric actin of the thin filament. Confocal images of Triton X-100-skinned myocytes incubated with a fluorescent conjugate of cytochalasin D revealed a longitudinally striated pattern of binding, consistent with a myofibrillar rather than cytoskeletal structure.Tension-pCa relationships were determined at sarcomere lengths (SLs) of 2.0 and 2.3 [mu]m following 2 min incubation with 1 [mu]M cytochalasin D. Cytochalasin D significantly reduced the pCa for half-maximal activation (pCa50) at both SLs. The shift in pCa50 was significantly greater at a SL of 2.3 [mu]m compared with that at a SL of 2.0 [mu]m. Cytochalasin D had no effect on the Hill co-efficient at either SL. Cytochalasin D significantly reduced the maximum tension at both SLs. We suggest that the length-dependent decrease in myofilament Ca2+ sensitivity in response to cytochalasin D is due to a decrease in the affinity of troponin C for Ca2+. Cytochalasin D has been used for many years as the agent of choice for disruption of cytoskeletal actin. However, we have demonstrated for the first time an interaction of cytochalasin D with sarcomeric actin of the thin filament, which can account for the effects of cytochalasin D on cardiac contractility.
authors: EA 2103 Lipides et Croissance Physiologique et Tumorale, Faculte de Medecine, 2 boulevard Tonnelle, 37032 Tours, France, School of Biomedical Sciences, University of Leeds, Leeds LS2 9JT, UK. s.c.calaghan@leeds.ac.uk
authors: S C
authors: SC
authors: Calaghan
authors: E
authors: E
authors: White
authors: S
authors: S
authors: Bedut
authors: J Y
authors: JY
authors: Le Guennec
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D015638:Cytochalasin D / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008856:Microscopy, Fluorescence; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D012518:Sarcomeres / Q000187:drug effects / Q000502:physiology*
chemical_list: D015638:Cytochalasin D; D002118:Calcium