Am. J. Respir. Cell Mol. Biol., Vol 15, No. 6, 12 1996, 726-730.
Molecular characterization of the human airway smooth muscle Na+/Ca2+ exchanger
A Pitt and AJ Knox
Department of Respiratory Medicine, City Hospital, Nottingham, United Kingdom.
The Na+/Ca2+ exchanger is an important plasma-membrane Ca2+ transport
protein. Functional studies of the effects of removal of external Na+ on
airway smooth muscle tone, and studies of Na+-dependent Ca2+ fluxes in
membrane vesicles have provided indirect evidence of an important role for
Na+/Ca2+ exchange in regulating airway smooth muscle tone. Recent molecular
studies have identified seven isoforms of the Na+/Ca2+ exchanger (NCX1)
gene in other tissues, but direct molecular characterization of the airway
smooth muscle Na+/Ca2+ exchanger has not previously been performed. We have
therefore used a reverse transcriptase-polymerase chain (RT-PCR) reaction
method and DNA sequencing to study the Na+/Ca2+ exchanger isoform present
in human airway smooth muscle. The dominant isoform was found to be
virtually identical to the NACA3 isoform originally described in rabbit
kidney cortex. The DNA sequence of the Na+/Ca2+ exchanger exon B that we
obtained is previously unpublished for any human tissue. This study
provides the first definitive molecular evidence of the existence of an
Na+/Ca2+ exchanger in airway smooth muscle. The molecular characterization
of the human airway smooth muscle Na+/Ca2+ exchanger will facilitate future
electrophysiologic studies of its function.
