Effect of aminophylline on calcium transport across the rat diaphragm

1. 1.|Calcium accumulation in muscle strips isolated from rat diaphragm reached steady state after 90 min with intracellular to extracellular ratio (IN/OUT) of 3.0. 2. 2.|Calcium uptake by rat diaphragm is a saturable and carrier mediated process that is significantly enhanced in the presence of aminophylline in a dose-dependent pattern that produced maximal effect at 18.75 μg/ml. 3. 3.|A Lineweaver-Burk plot shows J max = 25 μM/hr per g dry wt and K t = 3.19 mM for the control, and J max = 26 μM/hr per g dry wt and K t = 2.27 mM in the presence of 18.75 μg/ml aminophylline. 4. 4.|Aminophylline had no effect on cell volume and water of the diaphragmatic cells.