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The average thickness and distribution of airway surface liquid (ASL) on the luminal surface of peripheral airways were measured in normal guinea pig lungs frozen at functional residual capacity (FRC) and total lung capacity (TLC). Tissue blocks containing cross sections of airways of internal perimeter 0.188–3.342 mm were cut from frozen lungs and imaged by low-temperature scanning electron microscopy (LTSEM). Measurements made from LTSEM images were found to be independent of freezing rate by comparison of measurements at rapid and slow freezing rates. At both lung volumes, the ASL was not uniformly distributed in either the circumferential or longitudinal direction; there were regions of ASL where its thickness was < 0.1 micron, whereas in other regions ASL collected in pools. Discernible liquid on the surfaces of airways frozen at FRC followed the contours of epithelial cells and collected in pockets formed by neighboring cells, a geometry consistent with a low value of surface tension at the air-liquid interface. At TLC airway liquid collected to cover epithelial cells and to form a liquid meniscus, a geometry consistent with a higher value of surface tension. The average ASL thickness (h) was approximately proportional to the square root of airway internal perimeter, regardless of lung volume. For airways of internal perimeter 250 and 1,800 microns, h was 0.9 and 1.8 microns at FRC and 1.7 and 3.7 microns at TLC, respectively. For a given airway internal perimeter, h was 1.99 times thicker at TLC than at FRC; the difference was statistically significant (P < 0.01; 95% confidence interval 1.29–3.08).(ABSTRACT TRUNCATED AT 250 WORDS)

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The complete cDNA structure of the Ap1y.w californm pro-protein and pro-hormone convertase PC2 (aPC2) was obtained from a cDNA library of the nervous system. The deduced amino acid sequence revealed that aPC2 exhibits an 85%, 61% and 62% sequence identity to the L~~naea stagnalis, Xenopus laevis and mouse PC2 homologues, respectively. The deduced primary sequence suggested a protein of 653 ammo acids which includes a 27-and 88-amino acid signal peptide and pro-segment.The signal peptide and the C-termmal segments are the least conserved regions. On Northern blots of nervous system we detected a transcript of 6.8 kb. The m situ hybridization histochermstry on the abdominal ganglion revealed intense labeling of the bag cells. Large peptidergic cells and clusters of sensory and motor neurons also contained high levels of aPC2 mRNA.