Electrical and mechanical activity of isoproterenol-damaged frog heart.
The electrical and mechanical activities of myocardial strips from Rana pipiens were studied in the steady state at various stimulation frequencies and after a period of rest. The temperature of the bath was varied between + 12 and 35 degrees C. Normal myocardium was compared with that damaged by isoproterenol (ISO). The percentage change of action potential durations (APD50) and isometric force (P) was similar in ISO-damaged and control hearts at various bath temperatures with steady state stimulation rates between 20 and 100/min. At low stimulation rates (3-6/min) the prolongation of the action potential (AP) was more pronounced and the P-decrease was less in ISO-damaged myocardium compared to controls. These differences became more apparent at low bath temperatures. After 10 min of rest, APD50-90 was significantly prolonged in ISO-damaged heart and P was increased by a factor of 2 compared to controls (stimulation rate 20/min). Steady state values, on the other hand, were nearly the same in both groups. These findings are interpreted as indicating a temperature or ISO-dependent increase of electrogenic trans-sarcolemmal Ca2+-uptake during low frequency, or post-rest stimulation, either directly by an increase of the slow inward current (Isi), or indirectly by decreased K+-permeabilities.
Volkmann
R
R
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004553:Electric Conductivity / Q000187:drug effects; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D007545:Isoproterenol / Q000633:toxicity*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000473:pathology; D011894:Rana pipiens
D007545:Isoproterenol; D004837:Epinephrine