Ionic basis of the electrophysiological actions of adenosine on cardiomyocytes

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Abstract
The purpose of this review is to examine the role of the extracellular A1-adenosine (Ado) receptor in modulating membrane potential and currents in cardiac cells. The cellular electrophysiological effects of adenosine are both cell type- and species-dependent. In supraventricular tissues (SA, AV node, and atrium) of all species studied, the "direct" cAMP-independent activation of the inwardly rectifying K+ current IKAdo seems to be the most important action of adenosine. This current is activated by both adenosine and acetylcholine and flows through K+ channels with unitary slope conductance of about 45 pS and an open time constant of 1.4 ms. The density of K(+)-ACh,Ado channels is much less in ventricular than in atrial myocytes, and thus adenosine has little or no effect on the ventricular action potential. In atrial myocytes adenosine has a small inhibitory effect on basal L-type calcium current (ICa,L), but no effect on T-type calcium current (ICa,T). In ventricular myocytes, adenosine does not inhibi...

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