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 i ntervals, allowing rates of secretion to be calculated. We monitored 340 gl ands in 54 experiments with 12 sheep. Glands secreted basally at low rates (0.57 +/- 0.04 nl.min(-1).gland(-1), 123 glands) in tissues up to 9 h posth arvest and at lower rates for up to 3 days. Carbachol (10 muM) stimulated s ecretion with an early transient and a sustained or oscillating phase. Peak secretion was 15.7 +/- 1.2 nl.min(-1).gland(-1) (60 glands); sustained sec retion was 4.5 +/- 0.5 nl.min(-1).gland(-1) (10 glands). Isoproterenol and phenylephrine (10 mM each) stimulated only small, transient responses. We c onfirmed that cats have a large secretory response to phenylephrine (11.6 /- 3.7 nl.min(-1).gland(-1), 12glands),but pigs, sheep, and humans all have small responses (<2 nl.min(-1).gland(-1)). Carbachol-stimulated peak secre tion was inhibited 56% by bumetanide, 67% by HCO3- replacement with HEPES, and 92% by both. The distribution of secretion rates was nonnormal, suggest ing the existence of subpopulations of glands.