Hasselbach, Wilhelm Emeritus Group Biophysics, Max Planck Institute for Medical Research, Max Planck Society;
http://www.jbc.org/content/252/6/1950.full.pdf (Any fulltext)
Katz, A. M., Repke, D. I., Dunnett, J., & Hasselbach, W. (1977). Dependence of calcium permeability of sarcoplasmic reticulum vesicles on external and internal calcium ion concentrations. The Journal of Biological Chemistry, 252, 1950-1956.