Shuttleworth T J, Thompson J L
Department of Physiology, University of Rochester School of Medicine and Dentistry, New York 14642.
Am J Physiol. 1989 Nov;257(5 Pt 1):C1020-9. doi: 10.1152/ajpcell.1989.257.5.C1020.
Isolated cells from the nasal salt gland of ducklings (Anas platyrhynchos) were evaluated as a model system for the study of the muscarinic activation of exocrine ion secretion. Cells loaded with the fluorescent probe indo-1 were used to study changes in intracellular Ca2+ concentration [( Ca2+]i) after stimulation. Changes in inositol phosphate generation and oxygen consumption were also determined. Loading with the acetomethoxy ester form of indo-1 (indo-1/AM) was rapid, and intracellular cleavage of the ester was essentially complete. Leakage of the dye was negligible over the time course of measurements (up to 20 min). Resting [Ca2+]i was approximately 100 nM. Stimulation with carbachol resulted in progressive increases in the generation of inositol phosphates and rapid four- to fivefold increases in [Ca2+]i. At normal extracellular Ca2+ concentrations, [Ca2+]i remained elevated (approximately 3 times resting levels) for as long as stimulation continued. Experiments showed that the increases in [Ca2+]i were comprised of a combination of release of Ca2+ from intracellular stores and an enhanced entry of Ca2+ from the extracellular medium. It is specifically this latter process that produces the sustained elevations in [Ca2+]i that are the essential signal for secretory activity.
对来自小鸭（绿头鸭）鼻盐腺的分离细胞进行了评估，将其作为研究毒蕈碱激活外分泌离子分泌的模型系统。用荧光探针indo-1加载的细胞用于研究刺激后细胞内Ca2+浓度[（Ca2+]i）的变化。还测定了肌醇磷酸生成和耗氧量的变化。用indo-1的乙酰甲氧基酯形式（indo-1/AM）加载很快，酯的细胞内裂解基本完成。在测量过程（长达20分钟）中，染料泄漏可忽略不计。静息[Ca2+]i约为100 nM。用卡巴胆碱刺激导致肌醇磷酸生成逐渐增加，[Ca2+]i迅速增加四到五倍。在正常细胞外Ca2+浓度下，只要刺激持续，[Ca2+]i就会保持升高（约为静息水平的3倍）。实验表明，[Ca2+]i的增加由细胞内储存的Ca2+释放和细胞外介质中Ca2+的进入增强共同组成。正是后一过程产生了[Ca2+]i的持续升高，这是分泌活动的基本信号。
