胰腺腺泡细胞中持续性[Ca2+]i升高的特征及其与淀粉酶分泌的关系。

Characterization of sustained [Ca2+]i increase in pancreatic acinar cells and its relation to amylase secretion.

作者信息

Tsunoda Y, Stuenkel E L, Williams J A

机构信息

Department of Physiology, University of Michigan, Ann Arbor 48109.

出版信息

Am J Physiol. 1990 Nov;259(5 Pt 1):G792-801. doi: 10.1152/ajpgi.1990.259.5.G792.

DOI:10.1152/ajpgi.1990.259.5.G792

PMID:1700626

Abstract

The sustained increase in cytosolic free Ca2+ concentration ([Ca2+]i) during maximal stimulation of rat pancreatic acini with carbamylcholine (10(-5) M) was investigated in individual acinar cells by microspectrofluorometric analysis of fura-2. After the large initial [Ca2+]i increase from intracellular stores, [Ca2+]i remained significantly elevated as long as the stimulus was applied. The amplitude of this plateau was dependent on the median Ca2+ concentration ([Ca2+]o) being 45-50 nM above prestimulation in medium with 1 mM [Ca2+]o increasing to 90 nM at 10 mM [Ca2+]o. This Ca2+ plateau was completely blocked by 2.5 mM Ni2+ and 0.25 mM La3+ but was unaffected by elevated K+ or the Ca2+ channel blocker D 600. Mn2+ was able to enter the cytosol after the cell stimulation as indicated by intracellular quenching of fura-2, indicating that acinar cells possess a Mn2(+)-permeable Ca2+ channel. Elimination of [Ca2+]o or addition of Ni2+ and Mn2+ to the medium reduced the level of sustained amylase secretion in a reversible manner under superfusion conditions. Increasing [Ca2+]i above the normal level by increasing [Ca2+]o had no effect on amylase secretion. The process for sustained Ca2+ entry was pH sensitive; decreasing extracellular pH (pHo) to 6.5-6.8 during the cell stimulation resulted in a reduction of the sustained [Ca2+]i plateau level and a decrease in sustained amylase secretion. By contrast, increasing pHo to 8.0 enhanced the level of the sustained [Ca2+]i in a Ni2(+)-sensitive manner but did not increase amylase release. Changes in cytosolic pH had only minimal effects on the sustained [Ca2+]i plateau. The results demonstrate a receptor-mediated Ca2+ entry mechanism, which results in a small increase in [Ca2+]i important in the maintenance of sustained amylase release.

摘要

通过对fura-2进行显微分光荧光分析，在单个腺泡细胞中研究了用氨甲酰胆碱（10⁻⁵ M）最大刺激大鼠胰腺腺泡时胞质游离Ca²⁺浓度（[Ca²⁺]i）的持续升高情况。在最初因细胞内储存库导致的[Ca²⁺]i大幅升高之后，只要施加刺激，[Ca²⁺]i就会显著升高。该平台期的幅度取决于中位Ca²⁺浓度（[Ca²⁺]o），在含1 mM [Ca²⁺]o的培养基中比刺激前高45 - 50 nM，在10 mM [Ca²⁺]o时升至90 nM。此Ca²⁺平台期被2.5 mM Ni²⁺和0.25 mM La³⁺完全阻断，但不受高K⁺或Ca²⁺通道阻滞剂D 600的影响。如fura-2的细胞内淬灭所示，细胞刺激后Mn²⁺能够进入胞质，表明腺泡细胞具有一个对Mn²⁺通透的Ca²⁺通道。在灌流条件下，去除[Ca²⁺]o或向培养基中添加Ni²⁺和Mn²⁺以可逆方式降低了持续淀粉酶分泌水平。通过提高[Ca²⁺]o使[Ca²⁺]i高于正常水平对淀粉酶分泌没有影响。持续Ca²⁺内流过程对pH敏感；在细胞刺激期间将细胞外pH（pHo）降至6.5 - 6.8会导致持续[Ca²⁺]i平台期水平降低以及持续淀粉酶分泌减少。相反，将pHo提高到8.0以Ni²⁺敏感的方式提高了持续[Ca²⁺]i水平，但没有增加淀粉酶释放。胞质pH的变化对持续[Ca²⁺]i平台期只有最小影响。结果表明存在一种受体介导的Ca²⁺内流机制，这导致[Ca²⁺]i有小幅升高，对维持持续淀粉酶释放很重要。