Connexin-43-Mediated Gap Junction Coupling Between Adipocytes Regulates Norepinephrine-Induced Ca2+ Responses in Perivascular Adipose Tissue.

Anticontractile factors secreted by perivascular adipose tissue (PVAT) play an important role in regulating vascular tone. This process is driven by the neurotransmitter norepinephrine (NE), but recent data show that adrenergic innervation in PVAT is sparse. How limited innervation might initiate broad responses through PVAT depots remains unknown. Here, we used Ca2+ imaging with genetically encoded sensors, selective drugs, immunolabeling and a conditional ablation model to test the hypothesis that gap junction coupling among PVAT adipocytes contributes to how signals initiated by NE are distributed through PVAT depots. Despite exhibiting differing sensitivities to NE, adipocytes in aortic and mesenteric PVAT and in white adipose tissue displayed robust expression of the gap junction protein connexin-43 (Cx43). Blocking gap junction coupling with the drug carbenoxolone (Cbx) limited NE-evoked Ca2+ responses among adipocytes, while blocking Cx43 hemichannels with the mimetic peptide 43Gap26 had no significant effect. Fluorescence recovery after photobleaching (FRAP) in mPVAT was decreased in the presence of Cbx, suggesting impaired gap junction communication. Wire myography recordings of mesenteric arteries showed that the EC50 for NE was higher in samples with intact PVAT than those without; however, this effect was not significantly different in samples from mice that lacked Cx43 in adipocytes. Analysis of multiple connexins showed that adipocytes upregulate Cx26 gene expression when Cx43 is deleted. These observations support the conclusion that Cx43-mediated gap junction coupling among PVAT adipocytes contributes to distributing signals initiated by NE; however, how this mechanism contributes to regulating vessel constriction remains unclear. This, and how potential compensatory mechanisms are enacted in adipocytes lacking Cx43, should be addressed in future work.