Martínez-Zaguilán R, Wegner J A, Gillies R J, Hoyer P B
Department of Biochemistry, University of Arizona, Tucson 85724.
Endocrinology. 1994 Nov;135(5):2099-108. doi: 10.1210/endo.135.5.7956933.
This study was undertaken to characterize differences in Ca2+ homeostasis between small and large ovine luteal cells. Although increasing extracellular pH (pHex) resulted in increases in intracellular calcium ([Ca2+]in) in both cell types, the large cells exhibited a greater sensitivity, suggesting that distinct [Ca2+]in regulatory mechanisms with distinct pH optima are operating in the two cell types. The sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase inhibitors thapsigargin (TG) and cyclopiazonic acid (CPA) increased [Ca2+]in in both cell types. Treatment of small cells with CPA resulted in transient increases in [Ca2+]in, whereas CPA produced sustained increases in [Ca2+]in in large cells. In small cells, pretreatment with CPA prevented further increases in [Ca2+]in in response to TG and vice versa. In large cells, TG pretreatment precluded further increases in [Ca2+]in with either prostaglandin F2 alpha (PGF2 alpha) or CPA. In contrast, after CPA pretreatment, PGF2 alpha or TG induced further increases in [Ca2+]in in large cells. This suggests that a TG-sensitive, CPA-insensitive Ca2+ pool is present in large cells but not in small cells. Neither Na+ removal nor KCl addition affected [Ca2+]in in either cell type, indicating that neither the Na+/Ca2+ exchanger nor voltage-dependent Ca2+ channels are involved in Ca2+ homeostasis in these cells. Addition of the calcium antagonist, LaCl3 (La3+), produced a gradual increase in [Ca2+]in in large cells but no changes in [Ca2+]in in small cells. Additionally, treatment with increasing concentrations of 4-bromo-A23187 resulted in titratable increases in [Ca2+]in that are greater in large than small cells, suggesting that small cells possess a higher Ca(2+)-buffering capacity than large cells. Progesterone secretion by large cells was significantly inhibited at alkaline pHex. In the presence of PGF2 alpha, progesterone secretion exhibited a distinct pH optimum of 7.0. In contrast, pHex did not affect secretion of progesterone in small cells under any of the conditions tested. TG, CPA, and La3+ all reduced secretion of progesterone in large, but not small, cells. These results demonstrate that ovine large and small luteal cells differ in regulation of [Ca2+]in homeostasis, and that treatments that increase [Ca2+]in decrease progesterone secretion in large cells but have no effect in small cells.(ABSTRACT TRUNCATED AT 400 WORDS)
本研究旨在描述绵羊大、小黄体细胞之间钙离子稳态的差异。尽管细胞外pH值（pHex）升高会导致两种细胞类型的细胞内钙离子浓度（[Ca2+]in）增加，但大细胞表现出更高的敏感性，这表明两种细胞类型中存在具有不同pH最佳值的独特[Ca2+]in调节机制。肌浆网/内质网Ca(2+)-ATP酶抑制剂毒胡萝卜素（TG）和环匹阿尼酸（CPA）会增加两种细胞类型的[Ca2+]in。用CPA处理小细胞会导致[Ca2+]in短暂增加，而CPA会使大细胞中的[Ca2+]in持续增加。在小细胞中，用CPA预处理可防止因TG导致的[Ca2+]in进一步增加，反之亦然。在大细胞中，TG预处理可防止前列腺素F2α（PGF2α）或CPA导致的[Ca2+]in进一步增加。相反，在CPA预处理后，PGF2α或TG会使大细胞中的[Ca2+]in进一步增加。这表明大细胞中存在对TG敏感、对CPA不敏感的Ca2+池，而小细胞中不存在。去除Na+或添加KCl均不影响两种细胞类型的[Ca2+]in，这表明Na+/Ca2+交换器和电压依赖性Ca2+通道均不参与这些细胞的钙离子稳态。添加钙拮抗剂LaCl3（La3+）会使大细胞中的[Ca2+]in逐渐增加，但小细胞中的[Ca2+]in无变化。此外，用浓度递增的4-溴-A23187处理会导致[Ca2+]in呈可滴定性增加，大细胞中的增加幅度大于小细胞，这表明小细胞比大细胞具有更高的Ca(2+)-缓冲能力。在碱性pHex条件下，大细胞的孕酮分泌受到显著抑制。在存在PGF2α的情况下，孕酮分泌表现出明显的pH最佳值7.0。相反，在任何测试条件下，pHex均不影响小细胞中孕酮的分泌。TG、CPA和La3+均会降低大细胞而非小细胞中的孕酮分泌。这些结果表明，绵羊大、小黄体细胞在[Ca2+]in稳态调节方面存在差异，并且增加[Ca2+]in的处理会降低大细胞中的孕酮分泌，但对小细胞无影响。（摘要截选至400字）
