| Abstract: | The electrical and mechanical activities of myocardial strips from Rana pipiens treated with isoproterenol (ISO) were studied during cyanide hypoxia at different bath temperatures (12, 25 and 35 degrees C). In normal myocardium at 12 degrees C, the action potential duration (APD) was almost unchanged but the isometric force (P) was reduced to about 60% after 30 min in 3 mmol/l NaCN. At 25 degrees C, APD and P decreased to about 80 and 60%, respectively, after exposure to cyanide for 30 min. At 35 degrees C, a fast decrease of APD (to about 30%) and P (to about 10%) was seen within 30 min. In all cases, washout of cyanide interactions was possible. Large effects occurred when ISO-damaged myocardium was exposed to cyanide. During the initial 30 min of CN-treatment, APD and P were significantly reduced in the whole temperature range between 12 and 35 degrees C, when compared with controls. When the cyanide exposure times were long enough, all preparations developed contracture. Increase of the temperature and/or ISO-pretreatment shortened the time-course for resting tension increase. The effects of cyanide on APD and resting tension (RT) were strongly correlated and presumably a result of a cyanide-induced rise of the intracellular free calcium concentration (Ca2+i). |
