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

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Abstract

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 μM) and intracellularly injected cyclic AMP (0.15-10 μM). The adenosine reponse 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 K(d) for adenosine is 3.34 μM. 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 μM), though extracellular application of theophylline (1-100 μM) reversibly blocks the receptor. Occasionally, the H current is contaminated by a small C1- 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 ressponse is also observed but at very high concentrations of adenosine (>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.

Original languageEnglish
Pages (from-to)170-177
Number of pages8
JournalMolecular Pharmacology
Volume28
Issue number2
StatePublished - 1985

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