Oxalate transfer across the membranes of sarcoplasmic reticulum during the uptake of Ca++.
The kinetic profile of Ca++ uptake in the presence of oxalate is biphasic. An initial phase independent on oxalate is followed by an oxalate-dependent phase delayed in time. The ionophore X-537A only abolishes the net Ca++ uptake if added before the onset of the oxalate phase. However, during this phase, X-537A suddenly releases an amount of Ca++ similar in quantity to that released in the initial phase. The delay of the oxalate-dependent phase is a function of pH. At pH of about 5.5, the oxalate phase and simultaneous calcium oxalate precipitation would theoretically start at the beginning, with no delay. Ejection of protons during Ca++ uptake is strongly depressed by oxalate, but not by other organic anions which do not trap Ca++. It is suggested that oxalate is transferred to the inside of the vesicles as a monoprotonated species at expense of protons ejected by the Ca++-pump during the uptake of Ca++.
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002129:Calcium Oxalate / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D007832:Lasalocid / Q000494:pharmacology; D010070:Oxalates / Q000378:metabolism*; D019815:Oxalic Acid; D011522:Protons; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D010070:Oxalates; D011522:Protons; D002129:Calcium Oxalate; D019815:Oxalic Acid; D002118:Calcium; D007832:Lasalocid