Sawaki K, Baum B J, Roth G S, Ambudkar I S
Secretory Physiology Section, National Institute of Dental Research, National Institutes of Health, Bethesda, Maryland 20892, USA.
Arch Biochem Biophys. 1995 Oct 1;322(2):319-26. doi: 10.1006/abbi.1995.1470.
m3-Muscarinic cholinergic receptor (m3-AChR) and alpha 1-adrenergic receptor (alpha 1-AR) stimulation of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis (by a PIP2-specific phospholipase C, PLC) in rat parotid gland membranes is mediated via activation of alpha subunits of the Gq/11 family of G-proteins. This study examines m3-AChR and alpha 1-AR stimulation of PIP2 hydrolysis in membranes isolated from parotid glands of old (24 months) and young (3 months) rats (old and young rat membranes). Old rat membranes exhibited reduced stimulation of PIP2 hydrolysis in response to the addition of guanosine-5'-O-(3-thiotrisphosphate) (GTP gamma S) alone or GTP gamma S plus either carbachol (m3-AChR agonist) or epinephrine (alpha 1-AR agonist). This reduction in receptor-stimulated PIP2 hydrolysis was not due to a decrease in PLC activity per se since cholate-solubilized PLC activity was similar in old and young rat membranes. Additionally, these membranes exhibited comparable, immunologically detectable, levels of PLC beta 3, G alpha q/11, and G beta. In the presence of 10 microM AlCl3 and 10 mM NaF, stimulation of PIP2 hydrolysis in both old and young rat membranes was similar. Preincubation of membranes from old rats with GTP gamma S induced a time-dependent increase in the rate of PIP2 hydrolysis and, with 20 min preincubation, the rates of hydrolysis in old and young rat membranes were not statistically different. In aggregate, these data indicate that there is a defect in the activation of G alpha q/11 in parotid gland membranes from old rats.
毒蕈碱型胆碱能受体3（m3 - AChR）和α1 - 肾上腺素能受体（α1 - AR）对大鼠腮腺腺泡膜中磷脂酰肌醇4,5 - 二磷酸（PIP2）水解的刺激作用（通过PIP2特异性磷脂酶C，即PLC）是通过激活Gq/11家族G蛋白的α亚基介导的。本研究检测了老年（24个月）和幼年（3个月）大鼠腮腺分离膜（老年和幼年大鼠膜）中m3 - AChR和α1 - AR对PIP2水解的刺激作用。老年大鼠膜对单独添加鸟苷 - 5'-O -（3 - 硫代三磷酸）（GTPγS）或GTPγS加卡巴胆碱（m3 - AChR激动剂）或肾上腺素（α1 - AR激动剂）的反应中，PIP2水解的刺激作用降低。受体刺激的PIP2水解的这种降低并非由于PLC活性本身的降低，因为胆酸盐增溶的PLC活性在老年和幼年大鼠膜中相似。此外，这些膜显示出可比较的、免疫可检测水平的PLCβ3、Gαq/11和Gβ。在存在10μM AlCl3和10 mM NaF的情况下，老年和幼年大鼠膜中PIP2水解的刺激作用相似。用GTPγS预孵育老年大鼠的膜会导致PIP2水解速率随时间增加，预孵育20分钟后，老年和幼年大鼠膜中的水解速率无统计学差异。总的来说，这些数据表明老年大鼠腮腺腺泡膜中Gαq/11的激活存在缺陷。
