© 1995 by European Society of Cardiology
Copyright © 1995, European Society of Cardiology
Adenosine increases potassium conductance in isolated rabbit atrioventricular nodal myocytes
aDepartment of Medical Cardiology, Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, UK
bDepartment of Physiology and Pharmacology, University of Strathclyde, Glasgow, UK
* Corresponding author., Tel.: (+44-141) 552-3535; fax: (+44-141) 552-4683.
Objective: To study the actions of adenosine on the electrophysiology of spontaneously active, rod-shaped cells enzymatically isolated from rabbit atrioventricular (AV) node. Methods: Calcium-tolerant myocytes were isolated from the region of the AV node by enzymatic and mechanical dispersion. They were rod- or spindle-shaped, with spontaneous activity at 35–37 °C, and had higher membrane resistances (776 ± 283 M
, n = 13), compared to atrial cells (41 ± 18.2 M, n = 7; P < 0.001). Membrane potential, spontaneous action potentials and transmembrane ionic currents were studied using the whole-cell patch-clamp technique, in current-clamp and voltage-clamp mode. Results: Adenosine (0.1–50 µM) slowed or abolished the spontaneous activity, with hyperpolarisation of the membrane potential. Voltage-clamp experiments showed that adenosine induced an inwardly rectifying time-independent current. The adenosine-induced current was shown to be carried by potassium ions by the effect of increasing external potassium, which altered the reversal potential in accordance with the calculated potassium equilibrium potential. The A1 adenosine receptor antagonist, CPDPX (8-cyclopentyl-1,3-dypropylxanthine), reversed the effects of adenosine and an A1 receptor agonist, R-PIA [R(–)N6-(2-phenylisopropyl)adenosine] had effects similar to adenosine. Adenosine also caused a small decrease in inward calcium current (ICa) in some AV nodal cells. Conclusions: These results indicate that adenosine acts at A1 adenosine receptors to suppress spontaneous activity, hyperpolarise membrane potential and induce a time-independent potassium current in AV nodal cells. These actions, combined with reduction in inward calcium current in some cells, may underlie the negative chronotropic and dromotropic actions of adenosine on rabbit AV nodal cells.
KEYWORDS Adenosine; Atrioventricular node; A1-receptors; Potassium channel, background; Membrane potential; Rabbit, AV nodal cells
1 Permanent address: A.A. Bogomoletz Institute of Physiology, Bogomoletz Str. 4, 252601 GSP, Kiev 24, Ukraine.
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  A. J Workman, K. A Kane, and A. C Rankin Ionic basis of a differential effect of adenosine on refractoriness in rabbit AV nodal and atrial isolated myocytes Cardiovasc Res, September 1, 1999; 43(4): 974 - 984. [Abstract] [Full Text] [PDF]
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