Am. J. Respir. Cell Mol. Biol., Vol 13, No. 5, 11 1995, 563-569.
Expression of calcitonin gene-related peptide by cultured rat alveolar type II cells
RH Hastings and XY Hua
Department of Veterans Affairs Medical Center, San Diego, California 92161, USA.
Calcitonin gene-related peptide (CGRP) immunoreactivity is found in the
airways in terminals of primary sensory afferents, in neuroendocrine cells,
and in tracheal serous cells. This study shows that rat alveolar epithelial
cells express immunoreactive CGRP also. Freshly isolated cells contained 34
+/- 23 fmol CGRP/10(7) cells (n = 4). Cultured type II cells secreted CGRP
at a stable rate for 3 days after cell isolation, averaging 206 +/- 14 fmol
CGRP/well/day (750,000 cells plated/well with approximately 30%
efficiency). The extracellular CGRP immunoreactivity eluted in the same
fraction as rat CGRP-beta on high performance liquid chromatography.
Secretion of CGRP from type II cells was reversibly blocked by monensin, an
inhibitor of secretory protein transport. CGRP secretion was stimulated in
a concentration-dependent fashion by phorbol myristate acetate, but it was
not affected by forskolin, capsaicin, bradykinin, or nicotine. CGRP was not
detected in culture media from alveolar macrophages or fibroblasts,
potential contaminants of primary type II cell cultures. Calcitonin is
expressed by neuroendocrine cells, but it was not detected in conditioned
media from type II cell cultures. Thus, type II alveolar epithelial cells
express and secrete CGRP. Secretion occurs constitutively and is regulated
by a protein kinase C-dependent pathway. Secretion is unaffected by
increases in cyclic adenosine monophosphate or by treatments that induce
release of CGRP from sensory afferent nerve terminals in the airways.