Figure 2.

A. Effect of taurine on PLC activity; B. A proposed model for the mode of action of taurine on the IP3 pathway.A. Effect of taurine on PLC activity. 1). Control, 2). 0.25mM Glu, 3). 25mM taurine, 4). 25mM taurine plus 0.25mM Glu, 5). 10μM carbachol. The error bar indicates the standard deviation with N=3. Briefly, ³H-inositol was used as precursor for [³H]-phosphoinositides (PI). Hydrolysis of [PI] to inositol phosphates, [IP]_n, is an index of PLC activity. The experiments were performed as described previously [45]. Primary neuronal cultures in 35 mm dishes were first labeled with 8μCi of [³H, U]-inositol for 24 hours. The cells were washed with fresh medium containing 2mM LiCl (to prevent IP₃ dephosphorylation) and exposed to either Glu, taurine, or carbachol (a muscarinic cholinergic receptor agonist known to stimulate PLC), as indicated. Phosphoinositides, [PI], and inositol phosphates, [IP]_n, were determined from the organic phase and aqueous phase, respectively as described [45]. The results are expressed as the ratio of [IP]_n to [PI]. The results show that taurine reduces the production of basal level of [IP]_n by 20% (column 3) and Glu-stimulated increase of [IP]_n production by 40% (column 4). This coupled with the above results suggest that taurine may reduce the basal level or Glu-induced increase of poly-PI turnover through its inhibitory effect on PLC via inhibitory G-proteins e.g. G_i/G_o-like proteins. B. A proposed model for the mode of action of taurine on the IP3 pathway. Diagram illustrating that taurine’s action on taurine receptors results in an inhibition of PLC activity causing a reduction in IP3 formation thus reducing IP3 mediated release of calcium from internal stores.