Calcium uptake by sarcoplasmic reticulum of muscle grafts in rats

Cross transplantations were carried out in which the soleus (SOL) and extensor digitorum longus (EDL) muscles were switched to each other's muscle bed. Sixty days later, oxalate-supported calcium uptake was measured in homogenates of these grafts and compared with calcium uptake by homogenates of the contralateral control EDL and SOL muscles. With the incubation conditions used, calcium uptake was essentially limited to sarcoplasmic reticulum (SR) vesicles. The velocities of the initial rapid calcium uptake were compared in the grafts and control muscles. Subsequently calcium uptake slowed and the 30-min accumulation of calcium indicated the loading capacity of the SR. In control muscles, the EDL had a faster velocity (0.234 +/- 0.011 mumol/mg/min) of calcium uptake and higher capacity (0.527 +/- 0.017 mumol/mg) for calcium loading than the SOL (0.089 +/- 0.008 mumol/mg/min and 0.26 +/- 0.014 mumol/mg, respectively). The EDL grafts (originally SOL muscles) had faster calcium uptakes than the control SOL muscles or SOL grafts (0.196 +/- 0.013 versus 0.089 +/- 0.008 or 0.126 +/- 0.024 mumol/mg/min). Also, the calcium uptake capacities were higher in EDL grafts than in control SOL muscles (0.400 +/- 0.017 versus 0.261 +/- 0.014 mumol/mg), but not statistically higher than in SOL grafts (0.360 +/- 0.033 mumol/mg). In contrast, SOL grafts (originally EDL muscles) had slower calcium uptakes (0.126 +/- 0.024 mumol/mg/min) than did the control EDL muscles or EDL grafts and the calcium uptake capacities (0.360 +/- 0.033 mumol/mg) were lower in SOL grafts than in control EDL muscles, but not statistically lower than in EDL grafts.(ABSTRACT TRUNCATED AT 250 WORDS)