Adenosine Analogues Stimulate Cyclic AMP‐Accumulation in Cultured Neuroblastoma and Glioma Cells

Abstract

The effect of 3 stable adenosine analogues, L-phenylisopropyladenosine (L-PIA), 2-chloroadenosine and adenosine 5''-ethylcarboxamide (NECA), on cAMP accumulation was studied in 5 cell lines derived from the nervous system. In N18 neuroblastoma cells, with cholinergic properties, all 3 analogs caused an increased accumulation of cAMP with the following relative order of potency: NECA > 2-chloroadenosine > L-PIA. The half maximal effect of NECA was obtained at close to 10-8 M. In the 2 other neuroblastoma cell lines, 41A3 with cholinergic and NIE115 with adrenergic properties, the 2 analogues NECA and PIA had similar effects. In glioma C6 and 138 MG cells NECA was also more potent than PIA in elevating cAMP levels. The absolute potency of NECA in these cell lines was .apprx. 100-fold lower. Phosphodiesterase (PDE) activity in crude homogenates of the 5 cell lines showed essentially similar Km and Vmax, except for the 3 neuroblastoma cell lines showing-biphasic, and the glial cell lines showing monophasic Eadie-Hofstee plots. Theophylline was equally potent as an inhibitor of PDE in all cell lines, but the non-xanthine, inhibitor rolipram, was more potent against neuroblastoma than glial cell PDE. All 5 cell lines had adenosine receptors of the A2-subtype. The apparent affinity of the adenosine analogues to these receptors was markedly different between the neuroblastoma and glial cell lines. The absolute potency of adenosine analogues may have been a poor criterion to classify adenosine receptors into A1 and A2 subtypes, especially when intact cells were used.