Comparison of the effects of halothane on skinned myocardial fibers from newborn and adult rabbit. I. Effects on contractile proteins.
The effect of halothane on maximal and submaximal Ca2+-activated tension development of the contractile proteins of newborn and adult cardiac muscle from rabbits was determined. Right ventricular muscle was removed from newborn and adult rabbits, and the sarcolemma was disrupted (skinned) by homogenization. Fiber bundles were dissected from the homogenate and mounted on tension transducers. Fiber bundles were alternately immersed in relaxing solution [( Ca2+] less than 10(-9) M) and contracting solutions (various [Ca2+] from 10(-5.6) to 10(-3.8) M), which were saturated with 100% N2 alone or with three concentrations of halothane-N2 mixture. In the absence of halothane, newborn skinned myocardial fibers were slightly more sensitive to submaximal Ca2+ concentrations than were adult myocardial fibers. [Ca2+] required for 50% maximum tension were 10(-5.43) M and 10(-5.31) M, respectively (P less than 0.05). Halothane (1-3%) decreased the maximal Ca2+-activated tension (at [Ca2+] = 10(-3.8) M) similarly in adult and newborn myocardial fibers in a dose-dependent fashion. Tension was reduced by 5.9% for each 1% increase in halothane concentration. Halothane also decreased the sensitivity of adult myocardial skinned fibers to submaximal Ca2+ concentrations (10(-5.6) M to 10(-5.0) M) by shifting the Ca2+-tension response curve to the right. Only 3% halothane decreased the sensitivity of newborn myocardial skinned fibers to Ca2+. The authors conclude that halothane causes less depression of Ca2+ activation of the contractile proteins in newborn than adult rabbit myocardium and that this effect of halothane cannot account for greater negative inotropy of halothane in the newborn.
Krane
E J
EJ
Department of Anesthesiology, Children's Hospital and Medical Center, Seattle, Washington 98105.
Su
J Y
JY
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D003285:Contractile Proteins / Q000502:physiology*; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D011817:Rabbits
D003285:Contractile Proteins; D002118:Calcium; D006221:Halothane