Effects Of SKF83959 On HVA Ca²⁺ And Na⁺ Currents In Cultured Striatal Neurons Of Rat

Partâ… Activation of phosphatidylinositol-linked novel D₁ dopamine receptors inhibits high voltage activated Ca²⁺ currents in primary cultured striatal neuronsBackground: Recent evidences indicate the existence of a putative novel phosphatidylinositol (PI) -linked D₁ dopamine receptor in brain,and this receptor mediates excellent anti-Parkinsonian but less severe dyskinesia action. To further understand the basic physiological function of this receptor in brain, the effects of a phosphatidylinositol-linked D₁ dopamine receptor selective agonist SKF83959 on high voltage activated (HVA) Ca²⁺ currents in primary cultured striatal neurons were investigated. Methods: Using the whole-cell patch clamp technique and Calcium Image, we investigated the effects of SKF83959, a selective PI-linked D₁ dopamine receptors on IHVA in primary cultured striatal neurons. Results: (1) SKF83959 induced an inhibition of HVA Ca²⁺ currents in a dose dependent manner which exhibited voltage-independence. (2) Application of D₁ receptor antagonist, but not D₂,α1 adrenergic, 5-HT receptor or cholinergic antagonist attenuated SKF83959-induced reduction. (3) U73122 a selective PLC blocker), heparin (a IP₃ receptor antagonist), BAPTA (a Ca²⁺ chelator) and CsA (a calcineurin blocker) reduced significantly SKF83959-induced IHVA inhibitory modulation. (4)The inhibitory effects were attenuated significantly by the L-type calcium channel antagonist nifedipine. Conclusion: Our results demonstrated that SKF83959 -induced IHVA inhibitory modulation was a D₁ receptor-mediated event, assumed via PI-linked D₁ receptor. The modulation was mediated by activation of PLC, mobilization of intracellular Ca²⁺ stores and activation of calcineurin. Furthermore, L-type calcium channels involved in the regulation induced by SKF83959. These findings may help to further understand the functional role of the PI-linked dopamine receptor in brain. Partâ…¡SKF83959 Inhibits Na⁺ Currents in Primary Cultured Striatal Neurons via PLC_β-DAG-PKC-Signaling CascadeBackground: Regulation of voltage-gated sodium channels (VGSCs) is crucial to firing patterns that constitute the output of medium spiny neurons (MSN), projecting neurons of the striatum. This modulation is thus critical for the final integration of information processed within the striatum. It has been shown that activation of classic D₁-like dopamine receptor reduces sodium currents in MSN through channel phosphorylation by cAMP-dependent protein kinase. Recent evidences indicate the existence of a putative novel phosphatidylinositol (PI)-linked D₁ dopamine receptor in brain. However, it is unknown whether the novel PI-linked D₁ dopamine receptors could also modulate voltage-gated sodium channels within MSN. Methods: Using the whole-cell patch clamp technique and Western blotting, we investigated the effects of SKF83959, a selective PI-linked D₁ dopamine receptors on INa in primary cultured striatal neurons. Results: (1) Stimulation of SKF83959 induced an inhibition of INa in a dose dependent manner via D₁ receptor. (2) 1μM SKF83959 shifted the activation curve of INa positively and the voltage dependence of inactivation of INa was unaffected. (3) SCH23390(a D₁ dopamine receptor antaginist), U73122 ( a selective PLC blocker), BIM and chelerythrin (PKC blockers) reduced significantly SKF83959 induced inhibition of INa. Conclusion: Our results demonstrated that SKF83959 induced inhibition of INa was mediated by activation of phospholipase C (PLC), production of DAG, and activation of PKC. PKC phosphorylated the Na⁺ channel protein to inhibit INa. These data provides a fundation for understanding of the physiological function of the novel PI-linked dopamine receptor in brain.