The Role of Ryanodine and IP3-receptors in Calcium Responses to Tricyclic Antidepressants in Rat Neocortical Neurons

Tricyclic antidepressants, specifically amitriptyline (ATL) and desipramine (DES) are currently used to treat depression and chronic pain of various origins, in which NMDA receptor dysfunctions play an important role. The effect of therapeutic ATL concentrations on calcium-dependent desensitization of NMDA receptors, driven by the level of free calcium in the cytoplasm, is well documented. In addition, in cardiomyocytes, ATL and DES can cause calcium release into the cytoplasm from intracellular stores by opening inositol-3-phosphate receptor (IP3R) and/or ryanodine receptors (RyR) channels. This aspect of ATL and DES effects on neurons remains poorly understood. We studied the dependence of calcium responses to DES and ATL on the activation of IP3R and RyR in the endoplasmic reticulum (ER) and mitochondria of rat neocortical neurons in primary culture. Short-term (30 s) paired (at a 5-min interval) applications of 200 µM DES or 200 µM ATL elicited similar-magnitude calcium responses in cortical neurons. The use of RyR and IP3R antagonists showed that responses to ATL are blocked by the IP3R antagonist 2-APB (100 µM), while responses to DES are blocked by the RyR antagonist ryanodine (100 nM). Since the intracellular distribution of RyR and IP3R is non-homogenous, it can be assumed that DES and ATL stimulate calcium release from different calcium stores located either in different segments of the ER or in the ER and mitochondria. In addition, ATL and DES, being channel blockers of NMDA receptors, inhibited calcium entry from the extracellular space via activated NMDA receptors. Considering high DES and ATL concentrations (>100 µM) required for the stimulation of calcium release in neurons, it seems unlikely that such effects appear during their therapeutic action. However, the revealed specificity of DES and ATL for RyR and IP3R, respectively, can be used as a tool for experimental purposes.