Electrophysiological evidence for an ATP-gated ion channel in the principal cells of the frog skin epithelium

Citation
B. Brodin et R. Nielsen, Electrophysiological evidence for an ATP-gated ion channel in the principal cells of the frog skin epithelium, PFLUG ARCH, 439(3), 2000, pp. 227-233
Citations number
22
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physiology
Journal title
PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY
ISSN journal
0031-6768 → ACNP
Volume
439
Issue
3
Year of publication
2000
Pages
227 - 233
Database
ISI
SICI code
0031-6768(200001)439:3<227:EEFAAI>2.0.ZU;2-A
Abstract
In the present study we investigated the effects of adenosine 5'-triphospha te (ATP) on Na+ transport in frog skin epithelium. An experimental set-up w as constructed to allow simultaneous measurement of Na+ transport, measured as the amiloride-sensitive short circuit current (I-sc), and free cytosoli c Ca2+ concentration ([Ca2+](i)) measured with the Ca2+-sensitive dye fura- 2. The cell potential (V-sc) was measured with microelectrodes. Addition of ATP (100 mu M) to the basolateral solution resulted in a fast transient de crease in I-sc followed by a slower increase and a transient increase in [C a2+](i). Microelectrode measurements showed that the primary response, i.e. the decline in I-sc, was accompanied by transient depolarisation, followed by a return to the control value. The decrease in current was Ca2+ indepen dent; i.e. treatment with thapsigargin in Ca2+-free solutions abolished the Ca2+ transient but did not influence the current transient. The secondary response, i.e. the slow increase in current, was accompanied by slow depola risation of the cell. Measurements of apical Na+ permeability showed that t his was due to an opening or activation of apical Na channels. These data s how that ATP causes a fast initial drop and a secondary, long-lasting incre ase in Na+ absorption. The ability of ATP to cause the initial decline in c urrent is independent of Ca2+, i.e. it is not caused by secondary effects o f the P2Y-type receptors present in the tissue. Measurements of intracellul ar potential indicate that the initial depolarisation is caused by opening of non-selective cation channels, suggesting that this decrease is due to a transient activation of P2X-type ATP receptors.