An ATP‐activated conductance in pheochromocytoma cells and its suppression by extracellular calcium.

K. Nakazawa, K. Fujimori, A. Takanaka, K. Inoue

Research output: Contribution to journalArticle

117 Citations (Scopus)

Abstract

1. ATP‐activated inward current in PC12 pheochromocytoma cells was characterized using the whole‐cell voltage‐clamp technique. 2. ATP (100 microM) applied extracellular elicited an inward rectifying current with a reversal potential of about +7 mV. The current was desensitized in seconds in spite of continued presence of ATP. 3. A comparison was made of the ability of ATP and its analogues. The order of potency in activating the inward current was ATP greater than ATP gamma S greater than ADP; AMP, adenosine and alpha, beta‐methylene ATP were inactive at concentrations up to mM. 4. The ATP‐activated current was also observed when external Na+ and Ca2+ were replaced with K+, TEA, Tris or glucosamine. The order of ion selectivity was Na+ greater than K+ greater than TEA not equal to Tris greater than glucosamine. 5. The ATP‐activated current was also recorded in extracellular solutions containing Ca2+ as the only external cation. The amplitude increased as the concentration of Ca2+ was increased in the range between 1.8 and 16.2 mM. However, the current amplitude decreased at higher Ca2+ concentrations and the current was not recorded in 110 mM‐Ca2+ solution. 6. In the presence of 140 mM‐Na+ in the external solution, the current amplitude also decreased as the external Ca2+ concentration was increased (from 1.8 to 16.2 mM). 7. The results indicate that Ca2+ as well as monovalent cations permeate through the ATP‐sensitive pathway and that Ca2+ blocks ion permeation, including its own permeation through the pathway. This regulation by extracellular Ca2+ is different to the ATP‐activated current in smooth muscle cells.

Original languageEnglish
Pages (from-to)257-272
Number of pages16
JournalThe Journal of Physiology
Volume428
Issue number1
DOIs
Publication statusPublished - Sep 1 1990

All Science Journal Classification (ASJC) codes

  • Physiology

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