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Adenosine-induced K+ current in Xenopus oocyte and the role of adenosine 3',5'-monophosphate

I Lotan, N Dascal, Y Oron, S Cohen and Y Lass

Voltage clamp technique was used in Xenopus laevis oocytes in order to study and compare membrane currents evoked by extracellularly applied adenosine (0.1-10 microM) and intracellularly injected cyclic AMP (0.15- 10 microM). The adenosine response is a late long-lasting outward K+ current ("H" current), mediated by the Ra purine receptor subtype. The H current amplitude is directly proportional to (occupancy)3; the KD for adenosine is 3.34 microM. The H current is inhibited by the intracellular injection of protein kinase inhibitors, types II and III (5-450 ng/oocyte) and is usually potentiated by intracellular injection of theophylline (100-300 microM), though extracellular application of theophylline (1-100 microM) reversibly blocks the receptor. Occasionally, the H current is contaminated by a small Cl- current. The cyclic AMP current is also a long-lasting K+ outward current which is potentiated by extracellular theophylline (2 mM). Injection of cyclic AMP inhibits the membrane response to subsequent application of adenosine. The converse inhibition of a cyclic AMP response by an earlier adenosine response is also observed but at very high concentrations of adenosine (greater than 0.6 mM). It was shown by radioimmunoassay that extracellular adenosine increases the level of the intracellular cAMP within a few seconds by about 30%. Intracellular injection of a comparable amount of cAMP was shown to evoke a measurable K+ current. It is proposed that the adenosine-evoked K+ outward current is mediated by a rise in intracellular cAMP.

Volume 28, Issue 2, pp. 170-177, 08/01/1985
Copyright © 1985 by American Society for Pharmacology and Experimental Therapeutics




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B. F. King, S. S. Wildman, A. Townsend-Nicholson, and G. Burnstock
Antagonism of an Adenosine/ATP Receptor in Follicular Xenopus Oocytes
J. Pharmacol. Exp. Ther., June 1, 1998; 285(3): 1005 - 1011.
[Abstract] [Full Text]

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N Dascal, T. Snutch, H Lubbert, N Davidson, and H. Lester
Expression and modulation of voltage-gated calcium channels after RNA injection in Xenopus oocytes
Science, March 7, 1986; 231(4742): 1147 - 1150.
[Abstract] [PDF]


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Copyright © 1985 by the American Society for Pharmacology and Experimental Therapeutics