AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 3 418-R428, Copyright © 1983 by American Physiological Society
Pulmonary mechanoreceptors in the dipnoi lungfish Protopterus and Lepidosiren
R. G. DeLaney, P. Laurent, R. Galante, A. I. Pack and A. P. Fishman
Pulmonary mechanoreceptors in the dipnoi lungfish Protopterus aethiopicus
and Lepidosiren paradoxa were identified and characterized both in vivo and
in vitro. Both slowly adapting receptors (SAR) and rapidly adapting
receptors (RAR) were found, with the majority of receptors being of the
slowly adapting type. The SAR discharged during inflation once their
threshold volume was exceeded, and this activity persisted during prolonged
lung inflation. For most of the SAR, interaction between the rate of
inflation and lung volume was involved in setting the firing rate of the
receptor. Increase in intrapulmonary carbon dioxide partial pressure
decreased the activity of the SAR during sustained inflation at a constant
intrapulmonary pressure. The RAR also discharged during inflation once the
threshold volume was exceeded. However, in contrast to the SAR, the RAR
became silent within 1.5 - 15 s after the end of inflation. The activity of
these receptors during inflation was influenced predominantly by the rate
and influenced little by the volume of inflation. According to these
observations, the behavior of lungfish pulmonary mechanoreceptors closely
resembles that of pulmonary mechanoreceptors in amphibians but differs from
that of mechanoreceptors in the swim bladder of teleosts.
