Properties of substance P-stimulated mucus secretion from porcine tracheal submucosal glands. 
Human and pig airway submucosal glands secrete mucus in response to substance P (SubP), but in pig tracheal glands the response to SubP is >10-fold greater than in humans and shares features with cholinergically produced secretion.  CFTR-deficient pigs provide a model for human cystic fibrosis (CF), and in newborn CF pigs the response of tracheal glands to SubP is significantly reduced (Joo et al.  J Clin Invest 120: 3161-3166, 2010).  To further define features of SubP-mediated gland secretion, we optically measured secretion rates from individual adult porcine glands in isolated tracheal tissues in response to mucosal capsaicin and serosal SubP. Mucosal capsaicin (EC(50) = 19 μM) stimulated low rates of secretion that were partially inhibited by tetrodotoxin and by inhibitors for muscarinic, VIP, and SubP receptors, suggesting reflex stimulation of secretion by multiple transmitters.  Secretion in response to mucosal capsaicin was inhibited by CFTR(inh)-172, but not by niflumic acid.  Serosal SubP (EC(50) = 230 nM) stimulated 10-fold more secretion than mucosal capsaicin, with a V(max) similar to that of carbachol.  Secretion rates peaked within 5 min and then declined to a lower sustained rate.  SubP-stimulated secretion was inhibited 75% by bumetanide, 53% by removal of HCO(3)(-), and 85% by bumetanide + removal of HCO(3)(-); it was not inhibited by atropine but was inhibited by niflumic acid, clotrimazole, BAPTA-AM, nominally Ca(2+)-free bath solution, and the adenylate cyclase inhibitor MDL-12330A. Ratiometric measurements of fura 2 fluorescence in dissociated gland cells showed that SubP and carbachol increased intracellular Ca(2+) concentration by similar amounts.  SubP produced rapid volume loss by serous and mucous cells, expansion of gland lumina, mucus flow, and exocytosis but little or no contraction of myoepithelial cells.  These and prior results suggest that SubP stimulates pig gland secretion via CFTR- and Ca(2+)-activated Cl(-) channels.