Optical method for quantifying rates of mucus secretion from single submucosal glands

We describe an optical method to quantify single-gland secretion. Isolated tracheal mucosa were mounted at the air-Krebs interface and coated with oil. Gland secretions formed spherical bubbles that were digitally imaged at intervals, allowing rates of secretion to be calculated. We monitored 340 glands in 54 experiments with 12 sheep. Glands secreted basally at low rates (0.57 [+ or -] 0.04 nl [multiplied by] [min.sup.-1] [multiplied by] [gland.sup.-1], 123 glands) in tissues up to 9 h postharvest and at lower rates for up to 3 days. Carbachol (10 [micro]M) stimulated secretion with an early transient and a sustained or oscillating phase. Peak secretion was 15.7 [+ or -] 1.2 nl [multiplied by] [min.sup.-1] [multiplied by] [gland.sup.-1](60 glands); sustained secretion was 4.5 [+ or -] 0.5 nl [multiplied by] [min.sup.-1] [multiplied by] [gland.sup.-1] (10 glands). Isoproterenol and phenylephrine (10 [micro]M each) stimulated only small, transient responses. We confirmed that cats have a large secretory response to phenylephrine (11.6 [+ or -] 3.7 nl [multiplied by] [min.sup.-1] [multiplied by] [gland.sup.-1], 12 glands), but pigs, sheep, and humans all have small responses ([is less than] 2 nl [multiplied by] [min.sup.-1] [multiplied by] [gland.sup.1]). Carbachol-stimulated peak secretion was inhibited 56% by bumetanide, 67% by [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] replacement with HEPES, and 92% by both. The distribution of secretion rates was nonnormal, suggesting the existence of subpopulations of glands. carbachol; phenylephrine; cystic fibrosis transmembrane conductance regulator; lung disease; mucociliary clearance