Pysiological siginificance of 240K protein of vascular smooth muscle

点击翻译按钮获取中文摘要

To furhter clarify the role of phosphorylation of IP_3 receptor by protein kinase G (PKG) in the PKG induced stimulation of plasma membrane calcium pump (PMCA) of the vasucular smooth muscle, the effect of removal of IP_3 receptor on the stimulation was examed in the partially purified preparation of PMCA from porcine aorta, in which a definite stimulation of PMCA actrivity was observed upon activation of PKG.Contrary to expectation, removal of IP_3 receptor by specific immunoprecipitation with an antibody specific to type 1 IP_3 receptor did not affect the PKG stimulation of PMCA activity : the stimulation of PMCA was still observed even in the absence of IP_3 receptor. Furthermore, PKG stimulated PMCA in a highly purified preparation completely devoid of IP_3 receptor, only when the concentrations of PMCA were low (10 to 20nM), at which the enzyme is known to be in a monomeric form, while it failed to stimulate when the concentration of the enzyme was increased to 40 nM at which the enzyme is known to take an oligomeric form, and become fully actived and insensitive to calmodulin. Heat inactivated PKG,and PKG without cGMP did not produce stimulation. In addition, type Ialpha but not type Ibeta PKG was found to stimulate PMCA.It was concluded that PKG stimulates the PMCA in a monomeric form without phosphorylation of the ATPase, and that, of two PKG isozymes found in the vascular smooth muscle, only type Ialpha PKG participates in the stimulation.