Effects of XXXX on ventricular muscle from adult and neonatal @entity35 .

@entity141 @entity515 @entity2701 @entity520 @entity35
We compared the response of ventricular muscle from adult and neonatal @entity35 to @entity520 . In adult muscle, @entity520 caused an initial rapid fall of developed @entity2701 to 30 +/- 5% of control (mean +/- SEM, n = 6). However, @entity2701 recovered slowly to a steady state that was 56 +/- 6% of control. In neonatal muscle, @entity520 caused a significantly smaller initial fall in @entity2701 to 43 +/- 3% (n = 8, p less than 0.05), but the @entity2701 then showed a subsequent slower fall to a steady state that was 29 +/- 4% of control, significantly less than in the adult (p less than 0.01). We have attempted to identify the mechanisms underlying these differences in response. In detergent-skinned myofibrils, reducing the pH from 7.0 to 6.5 caused a reduction in the pCa50 of 0.61 units in the adult muscle, but only 0.27 units in the neonatal ventricular muscle. Myofibrillar @entity141 sensitivity in neonatal ventricular muscle is thus less susceptible to the effects of acidic pH than that of adult muscle. Since intracellular pH decreases rapidly on application of increased external @entity515 , these results are consistent with the finding that, initially, developed @entity2701 in neonatal muscles is less sensitive to the effects of @entity520 . Sodium dodecylsulfate gel electrophoresis of myofibrillar preparations from adult and neonatal @entity35 demonstrated differences in thin filament proteins, including troponin I, which may underlie the observed differences in @entity141 sensitivity. In adult @entity35 ventricular muscles, the slow recovery of @entity2701 during @entity520 is associated with an increase in the amplitude of the @entity141 transients to 263 +/- 34% of control (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)
