title: Studies on the calcium paradox phenomenon in cardiac muscle strips of poikilotherms.
abstract: Compared with hearts of homoiotherms at their body temperature, isometric strips from hearts of poikilotherms (G. morhua, P. flesus, R. pipiens, R. temporaria, X. laevis and V. berus) at their physiological temperatures showed an insignificant calcium paradox. In all strips Tmax (maximal contractile tension at Lmax) decreased rapidly upon Ca2+-deprivation. Upon Ca2+-restitution the recovery of Tmax generally decreased--but seldom stopped--with increased length of the Ca2+-free period. Quantitative differences in recovery were observed between the species. P (resting tension) was either unchanged or decreased during Ca2+-deprivation. During Ca2+-restitution P increased initially and thereafter decreased again. In most species the recovery of Tmax was the same at 22 degrees C as at 12 degrees C. Even at 32 and 36 degrees C (V. berus and R. pipiens, respectively) Tmax recovered somewhat. Ultrastructural effects of the Ca2+-deprivation-restitution--studied on R. pipiens--were most marked in the mitochondria, especially at 22 degrees C. At 36 degrees C even the controls were damaged.
mesh_terms: D000818:Animals; D001001:Anura; D002118:Calcium / Q000494:pharmacology*; D005399:Fishes; D066298:In Vitro Techniques; D008854:Microscopy, Electron; D008929:Mitochondria, Heart / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000648:ultrastructure; D012911:Snakes; D013045:Species Specificity; D013696:Temperature
chemical_list: D002118:Calcium