Vulnerability to calcium-induced neurotoxicity in cultured neurons expressing calretinin

Calretinin (CR) is a calcium-binding protein purported to have neuroprotect ive properties. This study was designed to characterize the types of neuron s containing CR in two different primary cultures and to determine which, i f any, CR-immunoreactive (CR-ir) neurons are resistant to excitotoxic insul ts. Calretinin-containing neurons in cortical primary cultures derived from E14 rat embryos were not resistant to either kainic acid or a brief calciu m overload induced by the calcium ionophore A23187. Equal proportions of CR -ir and GABAergic cortical neurons were lost after a 24-h exposure to 100 o r 500 mu M kainic acid. A 3 mu M, 3-h exposure to A23187 induced equivalent amounts of cell loss in both the total cell and CR-ir cortical neuron cult ure populations. Cortical cultures grown for 6-7 days were more vulnerable than 12- to 13-day-old cultures to short-term, low-concentration treatments of A23187. Older cultures, however, were more severely affected when exami ned 24 h after a 3-h exposure to A23187. Calretinin-immunoreactive neurons derived from the diencephalon were relatively more resistant than cortical neurons to kainic acid at 6-7 days in vitro. In cortical or diencephalic cu ltures, CR was rarely coexpressed with GABA or calbindin D-28k. No vasoacti ve intestinal peptide, substance P, or parvalbumin was detected in CR-ir ne urons in either culture system. We suggest that the presence of CR alone is not sufficient to spare neurons from a toxic calcium overload. Calretinin may still buffer calcium at low concentrations or be a component in a calci um-based signal transduction system, (C) 2000 Academic Press.