Involvement of HCN channels in diaphragmatic lymphatic pacemaking

Abstract

Pacemaking in spontaneously contracting lymphatics is thought to depend upon: a) small transient depolarisations sustained by an inward current through calcium‐dependent chloride channels, seen in mesenteric lymphatic vessels of guinea pigs, and, b) a current, observed only in bovine and sheep lymphatics, resembling cardiac If current. This study aimed at performing, a molecular, functional, and immuno‐hystological study to verify the potential involvement of hyperpolarization cyclic nucleotide gated (HCN) channels in pacing of intrinsic pumping activity. Experiments were performed in conformance with the FASEB Statement of Principles for the use of animals in research and education. After deep anesthesia, rat diaphragmatic specimens containing spontaneously contracting FITC‐dextran‐filled lymphatics were excised. Whole‐tissue perfusion with Ivabradine (300 mM) or CsCl (10 mM) caused a significant reduction in contraction frequency. CsCl also caused vasorelaxation and an increase in stroke amplitude. HCN channels were immunolocalised in the lymphatic vessel wall and this was further confirmed by RT‐PCR analysis of mRNA transcripts from the contracting vessels. Therefore, our results provide for the first time the molecular, functional, and immuno‐hystological evidences that HCN channels are responsible for pacemaking of lymphatic smooth muscle, setting the lymphatic vessel wall contractility.Supported by the FAR2014 Research fund by the University of Insubria