1. Physiology Department, Medical School, University of the Witwatersrand, Johannesburg, Republic of South Africa
2. Department of General Physiology, Dental School, University of the Witwatersrand, Johannesburg, Republic of South Africa
3. Medical Research Council Mineral Metabolism Research Unit, Department of Paediatrics, Baragwanath Hospital, University of the Witwatersrand, Johannesburg, Republic of South Africa