Churchill G C, Louis C F
Department of Biochemistry, University of Minnesota, St. Paul 55108, USA.
Invest Ophthalmol Vis Sci. 1997 Apr;38(5):855-65.
To identify agonists that elevate cytosolic Ca2+ (Cai2+) in lens cells and to characterize their mechanism of action.
Digital imaging and the Ca(2+)-reporting dye fura-2 were used to study the effects of agonists and their antagonists of Cai2+ in sheep lens primary cell cultures.
Exposing cells to adenosine triphosphate (ATP) and epinephrine increased Cai2+, whereas dopamine, 5-hydroxytryptamine, acetylcholine, histamine, kassinin, bradykinin, and glutamate did not elevate Cai2+. The ATP response was mediated by P2U purinergic receptors based on inhibition by the P2 antagonist suramin and the agonist rank potency order ATP = UTP = ATP gamma S > ADP > AMP > > adenosine; adenine, AMP-CPP, and AMP-PCP were inactive. The epinephrine response was mediated by alpha 1 adrenergic receptors based on the greater potency of the alpha 1 adrenergic selective antagonist prazosin compared to that of the alpha 2 adrenergic selective antagonist yohimbine. More specifically, the epinephrine response was mediated by the alpha 1A adrenergic receptor subtype based on the greater potencies exhibited by the alpha 1A subtype selective competitive antagonists WB 4101 and 5-methylurapidil compared to the alpha 1B and alpha 1D selective antagonists spiperone and BMY 7378, respectively. The agonist-mediated Cai2+ increase was dependent on intracellular Ca2+ stores and was inhibited by the phospholipase C inhibitor U73122. ATP or epinephrine could desensitize the cells to either agonist because of both the depletion of intracellular Ca2+ stores and the downregulation of a common intermediate in the signal transduction pathway.
Ca2+ is mobilized from intracellular stores in the sheep lens by ATP and epinephrine acting through P2U purinergic and the alpha 1A adrenergic receptors, respectively. This confirms previous reports of P2U receptors in lens and provides the first report of alpha 1A adrenergic receptors in the lens.
鉴定能升高晶状体细胞胞质Ca2+（Cai2+）的激动剂，并描述其作用机制。
利用数字成像技术和Ca(2+)报告染料fura-2研究激动剂及其对绵羊晶状体原代细胞培养物中Cai2+的拮抗剂的作用。
将细胞暴露于三磷酸腺苷（ATP）和肾上腺素可增加Cai2+，而多巴胺、5-羟色胺、乙酰胆碱、组胺、蛙皮素、缓激肽和谷氨酸盐不会升高Cai2+。基于P2拮抗剂苏拉明的抑制作用以及激动剂的效价顺序ATP = UTP = ATPγS > ADP > AMP > > 腺苷，ATP反应由P2U嘌呤能受体介导；腺嘌呤、AMP-CPP和AMP-PCP无活性。基于α1肾上腺素能选择性拮抗剂哌唑嗪比α2肾上腺素能选择性拮抗剂育亨宾更有效，肾上腺素反应由α1肾上腺素能受体介导。更具体地说，基于α1A亚型选择性竞争性拮抗剂WB 4101和5-甲基尿嘧啶分别比α1B和α1D选择性拮抗剂螺哌隆和BMY 7378表现出更高的效价，肾上腺素反应由α1A肾上腺素能受体亚型介导。激动剂介导的Cai2+增加依赖于细胞内Ca2+储存，并被磷脂酶C抑制剂U73122抑制。由于细胞内Ca2+储存的耗尽和信号转导途径中共同中间体的下调，ATP或肾上腺素可使细胞对任一激动剂脱敏。
ATP和肾上腺素分别通过P2U嘌呤能受体和α1A肾上腺素能受体作用，从绵羊晶状体的细胞内储存中动员Ca2+。这证实了先前关于晶状体中P2U受体的报道，并首次报道了晶状体中的α1A肾上腺素能受体。
