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Regulation of phosphoinositide cycle by intracellular sodium in the blood-brain barrier
R E Catalán1, A M Martínez, M D Aragonés
1Departamento de Biología Molecular, Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma de Madrid, Spain.
Abstract:
In the present study of cerebral microvessels, we report that monensin, a Na+ ionophore, elicits a decrease in 32P radioactivity incorporation into phosphoinositides in cerebral microvessels. In addition, monensin evokes enhanced production of inositol-1-monophosphate (IP) and inositol-1,4-bisphosphate (IP2), together with an increase in the diacylglycerol (DAG) mass. These results indicate that monensin evokes a phosphoinositide hydrolysis by phospholipase C (PLC). The absence of inositol-1,4,5-trisphosphate (IP3) production leads us to think that although phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis occurs in this process, there is a very rapid disappearance of IP3. The net decrease in 32P radioactivity incorporated into phosphoinositides suggests that a partial inhibition of their re-synthesis is also evoked. Experimental evidence with pharmacological tools suggests that: (1) these effects are secondary to an increase in Ca2+ through the Na+/Ca2+ exchanger; and (2) the intracellular Ca2+ release is not involved in these effects of monensin. Since some neuropeptide receptors in cerebral microvessels have been reported to be coupled to either the Na+/H+ exchanger or to PLC, we discuss the possibility that cross-talk exists between these intracellular signalling pathways (phosphoinositide metabolism and Na+ transport) in the blood-brain barrier (BBB).
Insights
Monensin, a Na+ ionophore, impacts cerebral microvessels by altering phosphoinositide metabolism and increasing intracellular calcium via the Na+/Ca2+ exchanger, suggesting pathway cross-talk in the blood-brain barrier.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Cerebral microvessels play a crucial role in blood-brain barrier (BBB) function.
- Intracellular signaling pathways regulate microvessel function and permeability.
- Phosphoinositide metabolism and ion transport are key signaling mechanisms.
Purpose of the Study:
- To investigate the effects of monensin, a Na+ ionophore, on phosphoinositide metabolism in cerebral microvessels.
- To elucidate the role of intracellular calcium and ion exchangers in monensin-induced signaling.
- To explore potential cross-talk between phosphoinositide metabolism and Na+ transport pathways in the BBB.
Main Methods:
- Measurement of 32P radioactivity incorporation into phosphoinositides.
- Quantification of inositol phosphates (IP, IP2, IP3) and diacylglycerol (DAG) mass.
- Pharmacological manipulation using ion channel blockers and assessment of intracellular Ca2+ changes.
Main Results:
- Monensin decreased 32P incorporation into phosphoinositides.
- Monensin enhanced inositol-1-monophosphate (IP) and inositol-1,4-bisphosphate (IP2) production, and increased diacylglycerol (DAG) mass, indicating phospholipase C (PLC) activation.
- Monensin-induced effects were secondary to increased intracellular Ca2+ via the Na+/Ca2+ exchanger, independent of intracellular Ca2+ release.
- A rapid disappearance of inositol-1,4,5-trisphosphate (IP3) and partial inhibition of phosphoinositide re-synthesis were observed.
Conclusions:
- Monensin activates phospholipase C (PLC) in cerebral microvessels, leading to phosphoinositide hydrolysis.
- The Na+/Ca2+ exchanger mediates monensin-induced intracellular Ca2+ increase, influencing signaling pathways.
- Evidence suggests cross-talk between phosphoinositide metabolism and Na+ transport in the blood-brain barrier (BBB).