Effects of Inorganic Phosphate on Calcium and Tension Oscillations in Saponin-Treated Rat Cardiac Muscle
The effects of inorganic phosphate (Pi) on the sarcoplasmic reticulum (s.r.) were studied in saponin-treated rat cardiac muscle. Ca2+-uptake and release by the s.r. was detected using Indo-1. Oscillations of Ca2+ and tension occurred when the [Ca2+] of the bathing solution was around the threshold for force production. Introduction of Pi (20mM) caused a slow transient release of Ca2+ from the s.r. The oscillations were abolished in the presence of Pi. Removal of Pi caused a rapid fall in Ca2+ followed by a large transient increase in [Ca2+] and tension. Results are consistent with a phosphate-induced decrease Ca2+ available for release.