Involvement of NO/sGC, but not ROCK, in histamine‐induced collecting lymphatic relaxation

Abstract

We hypothesized that histamine causes endothelial NO release, activating soluble guanylate cyclase (sGC), leading to inhibition of Rho Kinase (ROCK) to decrease lymphatic contractility. Isolated rat mesenteric collecting lymphatics displaying spontaneous contractions at a 2 cm H2O luminal pressure at 37ºC were studied before and after 10−6–10−4 M histamine treatment. Vessels were loaded with Fura‐2 to determine intracellular free calcium. The role of NO/sGC signaling was tested with 10−5 M L‐NAME or 10−4 M ODQ. The role of ROCK was investigated by transfecting vessels with constitutively active (ca)‐ROCK protein (2 μg/ml). Videos were acquired and end diastolic diameter (EDD), end systolic diameter (ESD), and contraction frequency were measured. Phasic contraction amplitude was calculated as AMP = EDD – ESD. Passive diameter (MaxD) was measured in Ca2+‐free Ringer's and used to normalize data and calculate tone: (MaxD‐EDD)/ MaxD)*100%. Histamine increased lymphatic EDD, decreased tone and AMP, and caused cessation of phasic contractions and associated Ca2+ transients. Pretreatment with L‐NAME or ODQ attenuated the response. Transfection of ca‐ROCK decreased EDD and increased tone within 5 min, but did not block histamine‐induced lymphatic relaxation. The data suggest that NO/sGC mediates histamine‐induced lymphatic relaxation, but inhibition of ROCK is not involved. Supported by NIH R01HL098215.