"CONTRACTILE INTERSTITIAL CELLS" IN PULMONARY ALVEOLAR SEPTA: A POSSIBLE REGULATOR OF VENTILATION/PERFUSION RATIO?

TLDR

Alveolar interstitial cells, comprising about half of the interstitial population, contain fibrillar bundles and are located in the thick air‑blood barrier surrounding pre‑ and post‑capillary vessels. The study aims to identify and characterize a novel contractile interstitial cell type distinct from smooth muscle within alveolar septa. In vitro experiments show that hypoxia or epinephrine induces contraction of alveolar tissue, supporting the existence of these contractile cells. Immunofluorescence reveals antiactin antibody binding in many interstitial cells, suggesting they may regulate ventilation‑perfusion ratio and indicating that the alveolus is not merely passive.

Abstract

In the lungs of healthy rats, humans, lambs, and monkeys, about 50% of the alveolar interstitial cells—resembling fibroblasts—contain bundles of fibrils measuring 30–80 Å in diameter. Immunofluorescence studies on frozen sections of rat lung demonstrate that many interstitial cells bind sera containing antiactin antibodies. On account of these two sets of findings and our additional in vitro studies suggesting alveolar tissue contraction due to hypoxia or epinephrine, we postulate that the alveolar septa contain contractile cells different from that of smooth muscle. For these cells we propose the name of "contractile interstitial cells." Such cells lie within the thick portion of the air-blood barrier and around the pre- or postcapillary vessels. Hence it is possible that they play a role in the autoregulation of ventilation/perfusion (V/Q) ratio, particularly in hypoxic pulmonary hypertension. These findings, demonstrating a contractile system other than bronchial and arterial smooth muscle, suggest that the alveolus should no more be conceived as a passive "organ."