Effects of increase in extracellular calcium on frequency-dependent inotropism in cardiac muscle.
Frequency-dependent effects on contractility in isolated rabbit papillary muscles were compared at different calcium concentrations ranging between 1 and 12.5 mM. Increase in extracellular calcium up to 3 mM resulted in an increase in the frequency-dependent positive inotropy. A further increase in extracellular calcium, up to 5 mM, brought about a quantitative decrease in the frequency-dependent positive inotropy. Still higher concentrations of extracellular calcium, 7.5 and 12.5 mM, altogether abolished the frequency-dependent increase in contractility. The latter at these concentrations of calcium was rather depressed in response to frequency increases. These characteristic changes in the frequency-dependent inotropism at different extracellular calcium concentrations may have been due to the occurrence of a moderate to severe intracellular calcium overload. It is suggested that heart function in certain cardiac diseases, associated with intracellular calcium overload, may not improve with an increase in heart rate.
Singal
P K
PK
Gupta
M
M
Prasad
K
K
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002304:Cardiac Pacing, Artificial; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects*; D007473:Ion Channels / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects; D011817:Rabbits
D007473:Ion Channels; D002118:Calcium