Although adenosine is known to activate K+ conduction in atrial tissue, there is still debate as to the involvement of cAMP-dependent mechanisms. In isolated adult guinea pig atrial myocytes, we demonstrate that the highly A1-selective adenosine receptor agonist 2-chloro-N6-cyclopentyladenosine reduced basal cAMP levels by 30-40% in the absence and presence of the nonxanthine phosphodiesterase ...

Using specific sensitive antisera against adenosine, we have immunocytochemically localized endogenous adenosine to specific layers of rat, guinea pig, monkey, and human retina. Highest adenosine immunoreactivity was observed in ganglion cells and their processes in the optic nerve fiber layer. Substantial staining was also found throughout the inner plexiform layer and in select cells in the i...

OBJECTIVE The aim of the present study was to assess the effects of A(1)-adenosine receptor (A1-AR) stimulation in ventricle of A(1)-adenosine receptor overexpressing mice (transgenic mice, TG). METHODS Effects of the A(1)-adenosine receptor agonist R-PIA ((-)-N(6)-phenylisopropyladenosine) on phosphorylation of phospholamban (PLB), Ca(2+) transients, Ca(2+) currents and cell shortening were ...

Adipocytes from hypothyroid rats do not respond to adrenaline with increased glycerol release. Adenosine deaminase largely restores lipolytic sensitivity. This effect is reversed by 2-deoxycoformycin, an inhibitor of the enzyme, and by N6-(phenylisopropyl)adenosine, which is not deaminated. Lipolytic response of normal cells to adrenaline is only 50% inhibited by phenylisopropyladenosine, where...

It has previously been shown that covalent incorporation of the photoreactive adenosine derivative (R)-2-azido-N6-p-hydroxy-phenylisopropyladenosine [(R)-AHPIA] into the A1 adenosine receptor of intact fat cells leads to a persistent activation of this receptor, resulting in a reduction of cellular cAMP levels [Mol. Pharmacol. 30:403-409 (1986)]. In contrast, covalent incorporation of (R)-AHPIA...

The density of adenosine receptors in membranes derived from rat hearts in 25 times lower than the density of receptors in rat brain membranes. Consequently, adenosine radioligands which are useful in brain such as l-[3H]phenylisopropyladenosine, [3H]cyclohexyladenosine, [3H]-2-chloroadenosine and l-[125I]hydroxyphenylisopropyladenosine are of limited usefulness in heart, due to a high ratio of...

We examined the mechanism by which adenosine inhibits prolactin secretion from GH3 cells, a rat pituitary tumour line. Prolactin release is enhanced by vasoactive intestinal peptide (VIP), which increases cyclic AMP, and by thyrotropin-releasing hormone (TRH), which increases inositol phosphates (IPx). Analogues of adenosine decreased prolactin release, VIP-stimulated cyclic AMP accumulation an...

We previously demonstrated that both adenosine receptor activation and direct activation of protein kinase C (PKC) decrease unloaded shortening velocity (V(max)) of rat ventricular myocytes. The goal of this study was to further investigate a possible link among adenosine receptors, phosphoinositide-PKC signaling, and V(max) in rat ventricular myocytes. We determined that the adenosine receptor...

Through immunocytochemistry with the use of antibodies against A1 adenosine receptors (A1Rs) and confocal microscopy, we show that stimulation of A1Rs by the agonist (R)-phenylisopropyladenosine [(R)-PIA] caused a rapid (5-15 min) aggregation (clustering) of receptor molecules on the surface of DDT1MF-2 cells. Internalization of the chronically stimulated receptor was slower and occurred concom...