Effect of aminophylline on calcium transport across the rat diaphragm

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. 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 micrograms/ml. A Lineweaver-Burk plot shows Jmax = 25 microM/hr per g dry wt and Kt = 3.19 mM for the control, and Jmax = 26 microM/hr per g dry wt and Kt = 2.27 mM in the presence of 18.75 micrograms/ml aminophylline. Aminophylline had no effect on cell volume and water of the diaphragmatic cells.