Adenosine receptors regulate gap junction coupling of the human cerebral microvascular endothelial cells hCMEC/D3 by Ca2+influx through cyclic nucleotide‐gated channels

Key points Gap junction channels are essential for the formation and regulation of physiological units in tissues by allowing the lateral cell‐to‐cell diffusion of ions, metabolites and second messengers. Stimulation of the adenosine receptor subtype A2Bincreases the gap junction coupling in the human blood–brain barrier endothelial cell line hCMEC/D3. Although the increased gap junction coupling is cAMP‐dependent, neither the protein kinase A nor the exchange protein directly activated by cAMP were involved in this increase. We found that cAMP activates cyclic nucleotide‐gated (CNG) channels and thereby induces a Ca2+influx, which leads to the increase in gap junction coupling. The report identifies CNG channels as a possible physiological link between adenosine receptors and the regulation of gap junction channels in endothelial cells of the blood–brain barrier. Abstract The human cerebral microvascular endothelial cell line hCMEC/D3 was used to characterize the physiological link between adenosine receptors and the gap junction coupling in endothelial cells of the blood–brain barrier. Expressed adenosine receptor subtypes and connexin (Cx) isoforms were identified by RT‐PCR. Scrape loading/dye transfer was used to evaluate the impact of the A2Aand A2Badenosine receptor subtype agonist 2‐phenylaminoadenosine (2‐PAA) on the gap junction coupling. We found that 2‐PAA stimulated cAMP synthesis and enhanced gap junction coupling in a concentration‐dependent manner. This enhancement was accompanied by an increase in gap junction plaques formed by Cx43. Inhibition of protein kinase A did not affect the 2‐PAA‐related enhancement of gap junction coupling. In contrast, the cyclic nucleotide‐gated (CNG) channel inhibitorl‐cis‐diltiazem, as well as the chelation of intracellular Ca2+with BAPTA, or the absence of external Ca2+, suppressed the 2‐PAA‐related enhancement of gap junction coupling. Moreover, we observed a 2‐PAA‐dependent activation of CNG channels by a combination of electrophysiology and pharmacology. In conclusion, the stimulation of adenosine receptors in hCMEC/D3 cells induces a Ca2+influx by opening CNG channels in a cAMP‐dependent manner. Ca2+in turn induces the formation of new gap junction plaques and a consecutive sustained enhancement of gap junction coupling. The report identifies CNG channels as a physiological link that integrates gap junction coupling into the adenosine receptor‐dependent signalling of endothelial cells of the blood–brain barrier.