IP(3)-sensitive Ca(2+)-channels of endoplasmic reticulum in secretory cells of the rat exorbital lacrimal gland

摘要

The role of inositol-1,4,5-trisphosphate of (IPsub3/sub)-sensitive Casup2+/sup channels in Casup2+/sup homeostasis maintenance under activation of M-cholinergic receptors and P2Y receptors in the secretory cells of the rat lacrimal gland was investigated. The study was carried out on intact and permeabilized secretory cells of exorbital lacrimal glands of rats. The cells were isolated using the modified Herzog, Sides, Miller method (1976) and permeabilized with digitonin (50 mg per 0.5 million cells). The functioning of the Casup2+/sup-transport systems was estimated by changes of Casup2+/sup content in the studied cells, which was determined by the spectrophotometric method using arsenazo III. It was shown that IPsub3/sub-sensitive Casup2+/sup channels (IPsub3/subRs) of investigated cells are directly inhibited by 2-APB (10 μM/l). On the other hand, the channels are activated by IPsub3/sub, cholinomimetic (carbacholine) and purine receptor agonist (ATP). When both M-cholinergic receptors and P2Y receptors were activated Casup2+/sup was released from the same IPsub3/sub-sensitive store because the effects of ATP and carbacholine at high concentrations (1 mM/l and 10 μM/l, respectively) on the Casup2+/sup content were non-additive. The presence of the store-operated Casup2+/sup-channels in secretory cells of the lacrimal gland is confirmed by the observed increase of cellular Casup2+/sup content as a result of Casup2+/sup mobilization from the store by carbacholine or thapsigargin and following restoration of Casup2+/sup concentration in the extracellular solution.