Properties of two calcium transport systems of isolated rat ileal epithelial cells: effects of Ca2+channel modulators and membrane potential examined with fluorescent dye, fura-2
✍ Scribed by Hiroyuki Hanai; Masaki Kameyama; Eizo Kaneko; Michiya Fujita
- Publisher
- Springer
- Year
- 1991
- Tongue
- English
- Weight
- 605 KB
- Volume
- 419
- Category
- Article
- ISSN
- 0031-6768
No coin nor oath required. For personal study only.
✦ Synopsis
Calcium transport systems of isolated ileal epithelial cells were investigated. The concentration of cytosolic free calcium ions, [Ca2 § was monitored with a fluorescent Ca 2+ dye, fura-2. The fluorescence intensity ratio (I34o/I38o) was used as an index of [Ca2+] i.
[Ca2+]i of the cells suspended in the nominally Ca2+-free solution was estimated at 52+3 nM. Ca 2+ uptake was followed for as long as 5 min in the presence of 100-1000 ktM added CaC12. Most of the experiments were performed at 200 ~tM CaC12. The Ca 2+ uptake was abolished by 0.8 mM Ni 2+ and 50 ~M Mn 2+ and partitally antagonized by 50 ~tM verapamil and 50 ~tM diltiazem but not affected by 20 ~tM nifedipine. The Ca 2+ entry was reduced by increasing concentrations of extracellular K + in the presence of valinomycin, suggesting a voltage-dependent nature of the uptake. On the other hand, the Ca z+ transport doubled in the presence of Bay K8644 (8 ~M), a Ca z+ channel agonist. The Bay-K-8644-induced uptake was inhibited by either 10 ~M nifedipine, 10 ~tM verapamil or 10 ~tM diltiazem and was relatively independent of extracellular K + concentration. These results suggest that there are at least two distinct Ca 2+ transport systems in the rat ileal epithelial cells, one resistant to organic Ca 2+ channel blockers but relatively sensitive to membrane potential (basal uptake) and another inducible by Bay K 8644 and sensitive to the channel blockers but relatively independent of membrane potential.