Dynamic calcium requirements for activation of rabbit papillary muscle calculated from tension-independent heat.
The heat generated by right ventricular papillary muscles of rabbits was measured after adenosine triphosphate (ATP) splitting by the contractile proteins was chemically inhibited. This tension-independent heat (TIH) (1 mJ/g wet weight) was used to calculate the total calcium (Ca) cycled in a muscle twitch by assuming that 87% of TIH was due to Ca2+ transport by the sarcoplasmic reticulum with a coupling ratio of 2 Ca2+/ATP split; the enthalpy of creatine phosphate hydrolysis buffering ATP was taken as -34 KJ/mol. The estimated Ca turnover per muscle twitch at 21 degrees C, 0.2 Hz pacing rate, and 2.5 mM Ca in the Krebs solution was approximately equal to 50 nmol/g wet weight. There was a tight positive correlation between TIH and mechanical activation during steady-state measurements but no correlation during the sharp increase in mechanical activation (treppe) when stimulation was resumed after a rest period. It is suggested that while total Ca cycling remains unchanged during the initial period of tension treppe, the free Ca2+ transient and mechanical activation increase sharply due to resaturation of high affinity Ca2+ buffers, other than troponin C, depleted of Ca2+ during the rest period.
Blanchard
E M
EM
Department of Physiology and Biophysics, University of Vermont College of Medicine, Burlington 05405.
Mulieri
L A
LA
Alpert
N R
NR
D008841:Actin Cytoskeleton / Q000201:enzymology / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000493:pharmacokinetics; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics*; D000252:Calcium-Transporting ATPases / Q000493:pharmacokinetics; D004558:Electric Stimulation; D006358:Hot Temperature; D009200:Myocardial Contraction / Q000502:physiology*; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology* / Q000648:ultrastructure; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism
D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium