Morán J, Morales-Mulia M, Pasantes-Morales H
Department of Neurosciences, Institute of Cell Physiology, National University of Mexico.
Biochim Biophys Acta. 2001 Apr 23;1538(2-3):313-20. doi: 10.1016/s0167-4889(01)00082-9.
The role of phospholemman (PLM) in taurine and Cl(-) efflux elicited by 30% hyposmotic solution was studied in cultured cerebellar astrocytes with reduced PLM expression by antisense oligonucleotide (AO) treatment. PLM, a substrate for protein kinases (PK) C and A, is a protein that increases an anion current in Xenopus oocytes and forms taurine-selective channels in lipid bilayers. Taurine contributes as an osmolyte to regulatory volume decrease (RVD) and is highly permeable through PLM channels in bilayers. Two antisense oligonucleotides (AO1 and AO2) effectively decreased the expression of the PLM protein by 40% and 30%, respectively, and markedly reduced [(3)H]taurine efflux by 67% and 62%. AO treatment also decreased the osmosensitive release of Cl(-), followed as (125)I. The inhibition of Cl(-) efflux (23% for AO1 and 13% for AO2) was notably lower than for [(3)H]taurine. The contribution of PKC and PKA in the function of PLM was also evaluated in astrocytes. Pharmacological activation or inhibition of PKC and PKA revealed that the osmosensitive taurine efflux is essentially PKC-independent while (125)I efflux is reduced by the PKC blockers H-7 (21%) and Gö6983 (41%). The PKA activator forskolin and dbcAMP increased taurine efflux by 66-70% and (125)I efflux by 21-45%. Norepinephrine increased the osmosensitive taurine efflux at about the same extent as dbcAMP and forskolin, and this was reduced by PKA blockers. These results suggest that PLM plays a role in RVD in astrocytes by predominantly influencing taurine fluxes, which are modulated by PKA but not PKC.
通过反义寡核苷酸（AO）处理降低培养的小脑星形胶质细胞中磷膜蛋白（PLM）的表达，研究了PLM在30%低渗溶液引发的牛磺酸和Cl⁻外流中的作用。PLM是蛋白激酶（PK）C和A的底物，是一种能增加非洲爪蟾卵母细胞阴离子电流并在脂质双分子层中形成牛磺酸选择性通道的蛋白质。牛磺酸作为一种渗透溶质有助于调节性容积减小（RVD），并且在双分子层中可通过PLM通道高度通透。两种反义寡核苷酸（AO1和AO2）分别有效降低了PLM蛋白表达的40%和30%，并显著降低了[³H]牛磺酸外流的67%和62%。AO处理还降低了Cl⁻的渗透敏感性释放，其通过¹²⁵I进行追踪。Cl⁻外流的抑制（AO1为23%，AO2为13%）明显低于[³H]牛磺酸。还在星形胶质细胞中评估了PKC和PKA在PLM功能中的作用。PKC和PKA的药理学激活或抑制表明，渗透敏感性牛磺酸外流基本上不依赖PKC，而¹²⁵I外流则被PKC阻滞剂H-7（21%）和Gö6983（41%）降低。PKA激活剂福斯可林和二丁酰环磷腺苷（dbcAMP）使牛磺酸外流增加了66 - 70%，使¹²⁵I外流增加了21 - 45%。去甲肾上腺素使渗透敏感性牛磺酸外流增加的程度与dbcAMP和福斯可林大致相同，并且这被PKA阻滞剂降低。这些结果表明，PLM主要通过影响牛磺酸通量在星形胶质细胞的RVD中发挥作用，牛磺酸通量由PKA而非PKC调节。
