β-adrenergic neurotransmission is an important factor regulating brain activity such as neuronal and glial survival, plasticity, membrane transport or cellular metabolism. Intracellular β-adrenergic signaling, via a stimulatory G protein (Gs), activates two major down-stream effectors, i.e., adenylyl cyclase (AC) and cAMP-dependent protein kinase A (PKA). The aim of this work was to study the ability of endogenous (adrenaline and noradrenaline) and exogenous (isoprenaline) β-adrenergic receptor agonists to increase cAMP in different types of nerve cells. Moreover, we wanted to precisely identify the receptor isoform involved in the observed phenomenon using selective β1-, β2- β3-adrenoceptor blockers. In an additional study, the negative influence of hypoxia on the AC/cAMP intracellular signaling system was tested. The study was conducted in parallel on rat primary glial (astrocytes) cultures, primary neuronal cultures, C6 glioma cells and human T98G glioma cells. The formation of [^(3)H] cAMP by agonists and antagonists was measured in [^(3)H] adenine prelabeled cells under normoxic and hypoxic conditions. The obtained results revealed that adrenaline, noradrenaline and isoprenaline strongly stimulated cAMP production in all tested cell types (with highest potency in C6 glioma cells). In glial and neuronal cells the adrenaline-evoked cAMP effect was mediated mainly by the β1-adrenoceptor, whereas in tumor cells the effect was probably mediated by all three β-subtype specific drugs. The AC/cAMP intracellular signaling system is affected by hypoxic conditions. Considering both physiological and therapeutic importance of β-family receptors the present work characterized the β-adrenoceptor-mediated cAMP signal transduction pathway in different nerve cells in normoxic and hypoxic conditions. The proposed in vitro model of hypoxic conditions may serve as a good model system to study the biological effects of endogenous catecholamines as well as potential therapeutics targeting adrenergic receptors, which are impaired during ischemia in vivo.
Keywords: astrocytes; hypoxia; neurons; tumor cells; β -adrenergic receptors.