Adrenergic stimulation of single rat astrocytes results in distinct temporal changes in intracellular Ca2+ and cAMP-dependent PKA responses

• Activation of α1-ARs in astrocytes leads to phasic Ca2+ oscillations.
• Activation of β-ARs causes a tonic rise in cAMP/PKA activity devoid of oscillations.
• Ca2+ rise occurs within 10 s, 10-fold faster than the rise in PKA activity.
• α1-AR activation potentiates β-AR-induced cAMP response and vice versa.

During the arousal and startle response, locus coeruleus neurons, innervating practically all brain regions, release catecholamine noradrenaline, which reaches neural brain cells, including astrocytes. These glial cells respond to noradrenergic stimulation by simultaneous activation of the α- and β-adrenergic receptors (ARs) in the plasma membrane with increasing cytosolic levels of Ca2+ and cAMP, respectively. AR-activation controls a myriad of processes in astrocytes including glucose metabolism, gliosignal vesicle homeostasis, gene transcription, cell morphology and antigen-presenting functions, all of which have distinct temporal characteristics. It is known from biochemical studies that Ca2+ and cAMP signals in astrocytes can interact, however it is presently unclear whether the temporal properties of the two second messengers are time associated upon AR-activation. We used confocal microscopy to study AR agonist-induced intracellular changes in Ca2+ and cAMP in single cultured cortical rat astrocytes by real-time monitoring of the Ca2+ indicator Fluo4-AM and the fluorescence resonance energy transfer-based nanosensor A-kinase activity reporter 2 (AKAR2), which reports the activity of cAMP via its downstream effector protein kinase A (PKA). The results revealed that the activation of α1-ARs by phenylephrine triggers periodic (phasic) Ca2+ oscillations within 10 s, while the activation of β-ARs by isoprenaline leads to a ∼10-fold slower tonic rise to a plateau in cAMP/PKA activity devoid of oscillations. Thus the concomitant activation of α- and β-ARs triggers the Ca2+ and cAMP second messenger systems in astrocytes with distinct temporal properties, which appears to be tailored to regulate downstream effectors in different time domains.

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