[³H]taurine andd-[³H]aspartate release from astrocyte cultures are differently regulated by tyrosine kinases

Abstract

Volume-dependent anion channels permeable for Cl− and amino acids are thought to play an important role in the homeostasis of cell volume. Astrocytes are the main cell type in the mammalian brain showing volume perturbations under physiological and pathophysiological conditions. We investigated the involvement of tyrosine phosphorylation in hyposmotic medium-induced [3H]taurine andd-[3H]aspartate release from primary astrocyte cultures. The tyrosine kinase inhibitors tyrphostin 23 and tyrphostin A51 partially suppressed the volume-dependent release of [3H]taurine in a dose-dependent manner with half-maximal effects at ∼40 and 1 μM, respectively. In contrast, the release ofd-[3H]aspartate was not significantly affected by these agents in the same concentration range. The inactive analog tyrphostin 1 had no significant effect on the release of both amino acids. The data obtained suggest the existence of at least two volume-dependent anion channels permeable to amino acids in astrocyte cultures. One of these channels is permeable to taurine and is under the control of tyrosine kinase(s). The other is permeable to both taurine and aspartate, but its volume-dependent regulation does not require tyrosine phosphorylation.

Potentiation of the Osmosensitive Release of Taurine and d-Aspartate from SH-SY5Y Neuroblastoma Cells after Activation of M3Muscarinic Cholinergic Receptors

“…This differential ability of DIDS and SITS to preferentially block taurine release has previously been observed for other neural preparations and has led to the speculation that more than one VSOAC channel may mediate osmolyte efflux (Rutledge et al, 1998;Franco et al, 2001;Ochoa de la Paz et al, 2002). Although this remains a possibility for osmolyte efflux from SH-SY5Y cells, further evidence to support the concept of multiple VSOACs, e.g., from 1) differences in the rate of activation and deactivation of the release of individual osmolytes (Franco et al, 2001) and 2) differential inhibition of osmolyte release by tyrosine kinase inhibitors (Mongin et al, 1999;Franco et al, 2001;Ochoa de la Paz et al, 2002) was not obtained in the present study. Thus, although our data do not exclude the possible involvement of multiple VSOACs, the most parsimonious interpretation is that under both basal-and agonist-stimulated conditions, the efflux of taurine and D-aspartate from SH-SY5Y cells occurs predominantly via the same (or very similar) VSOAC channel(s).…”

“…We have now extended these initial findings in SH-SY5Y cells by examining the efflux of two additional osmolytes, namely, taurine and D-aspartate (as a marker for glutamate efflux), which, due to their molecular dimensions, are more readily released by hypoosmotically stressed cells than myo-inositol. The monitoring of both these osmolytes addresses the possibility of the existence of distinct VSOACs specific for each osmolyte and potentially exhibiting different properties (Mongin et al, 1999;Franco et al, 2001;Ochoa de la Paz et al, 2002). The specific objectives of the present study were to 1) monitor taurine and D-aspartate release from SH-SY5Y cells under conditions of relatively limited alterations in osmolarity (such as those that might be encountered in vivo), in the absence and presence of mAChR activation; 2) pharmacologically identify the mAChR subtype coupled to enhanced osmolyte efflux; 3) determine whether the VSOAC mediates both the basal-and agonist-mediated efflux of taurine and D-aspartate; and 4) determine the role, if any, played by tyrosine kinase activity in agonist-stimulated osmolyte release.…”

Role of volume-regulated and calcium-activated anion channels in cell volume homeostasis, cancer and drug resistance

“…13,88,89 VRAC vs. VSOAC The molecular identity of VSOAC has been controversial and more than one channel has been demonstrated to be involved in release of organic osmolytes. 90 VRAC has been suggested as a VSOAC candidate 53,91 and as indicated below the discovery of LRRC8 family members as essential components of VSOAC and VRAC 2,4 nourishes this hypothesis. However, there are discrepancies between VSOAC and VRAC, i.e., differences in (i) time course for swelling induced activation/inactivation of taurine (VSOAC) and I -(tracer for Cl -, VRAC) (Fig.…”

Physiology of Cell Volume Regulation in Vertebrates

“…Interestingly, the increased ROS production following hypotonic exposure in, e.g., NIH3T3 cells appears to both potentiate the signaling cascade leading to the activation of the efflux pathway, and delay the inactivation of the pathway (494). A role for tyrosine phosphorylation events in modulation of swelling-induced taurine release is suggested by the inhibitory effect of tyrosine kinase blockers (genistein, tyrphostins) and potentiating effect of tyrosine phosphatase inhibitors on the efflux (492,662,670,920). Pharmacological evidence indicates that the tyrosine kinases regulating the taurine efflux pathway include receptor tyrosine kinases (247,492), FAK, and members of the Src family (391, 492).…”