Adenosine A1 receptor-induced inhibition of Ca2+ transients linked to action potentials in clonal pituitary cells (original) (raw)

1991, European Journal of Pharmacology: Molecular Pharmacology

Adenosine is a poten', paracfine/antocrine feedback inhibitor of cell activation in a variety of tissues. Adenosine action ~'a~ studied in pituitapj cells, in which spontaneous electrical activity causes characteristic oscillations of the cytosofic free Ca 2 concentration, [CaX+],. Cells of the GHsB6 rat pituitary tumor line were studied by rmcrospectrofluorimetry using the Ca 2" probes indo~l and fura-2, in putt in combination with electrophysiologJcal tight seal whole cell recordings, obtain~.e.d with the novel approach of patch perforation. It was demonstrated that adenosine receptor activation by N6-(R-phenyl-isopropyl)-adenosine (PIA) caused a block of electrical activity and abolished the ensinng alterations in [Ca 2+ ]i-PIA mimicked the inl',Jbitory ~ action of somatostatin. Adenosine effects are mediated by A 1 receptors in these cells and are antagoinzed by 1BMX. an adenosine receptor blocker. PIA also suppressed action potentials that were elicited by the activation of protein kinase C with the phorbol ester PMA, or during the second phase of TRH action. In contrast, no interference was notable on TRH-induced intracellular Ca 2. mobilization. In addition to the abolition of Ca 2+ transients, PIA lowers basal [Ca2+]i in some cells. It is proposed that in addition to the inhibition of adenylate cyclase, A 1 receptor action on [Ca2÷]i is an important element in the control of excitable pituitary cells.

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