title: The effect of rate, paired pacing and calcium on the length-tension relations in the rabbit papillary muscle.
abstract: The effect of sustained paired pacing, extracellular Ca2+ concentration and of the rate of steady-state single pacing on the length-tension relations in the isolated papillary muscles of right ventricles of rabbit hearts was investigated. We found that full range change of contractile force (CF, from close to zero to maximal) may be obtained by means of the change of the resting muscle length by 10-15% of Lmax (the length at which CF is maximal). This change brings about the shift of the thin filaments of the sarcomeres along the thick ones by one sixth of their length. The only effect of all the applied interventions could be reproduced by multiplying CF at each length step by some coefficient. Neither of them did change the basic pattern of length-tension relations. These results are compatible with the hypothesis that the basic mechanism of length-tension relations is the change of sensitivity of contractile system to the sarcoplasmic Ca2+ concentration.
mesh_terms: D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004558:Electric Stimulation; D005260:Female; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011817:Rabbits
chemical_list: D002118:Calcium