Molecular cloning, functional analysis and unique tissue distribution of a
human, amiloride resistant, na+/h+ exchanger isoform, nhe3.
Brant, Steven R., C. H. Chris Yun, Mark Donowitz, and Chung-Ming Tse.
Departments of Medicine and Physiology, Gastroenterology Division, The
Johns Hopkins University School of Medicine, Baltimore, Maryland, 21205
APStracts 2:0071C, 1995.
We previously isolated a 1.4 kb partial cDNA from a human kidney cortex
library. Using both library screening and RT-PCR of human kidney RNA, we
obtained the entire coding region of the human NHE3 cDNA. The human NHE3 cDNA
encoded a protein of 834 amino acids with a calculated Mr of 92,906. It
exhibited 89% and 88% amino acid identity with rat and rabbit NHE3,
respectively. The stable transfection of a composite human NHE3 cDNA into
Na+/H+ exchanger deficient PS120 cells established Na+/H+ exchange.
Functionally, human NHE3 was similar to the rabbit and rat NHE3 homologues,
being relatively resistant to inhibition by amiloride, IC50 = 49.0 [mu]M, and
ethylisopropylamiloride, IC50 = 6.6 [mu]M, and being stimulated by fibroblast
growth factor (FGF) but inhibited by phorbol 12-myristate 13-acetate (PMA).
However, unlike the rabbit or rat, human NHE3 message was not restricted to
kidney, intestine, stomach and brain. Northern analysis of multiple human
tissues detected NHE3 message, in descending order, as follows: kidney >>
small intestine >> testes > ovary > colon = prostate > thymus > peripheral
leukocyte = brain > spleen > placenta. Message in the kidney, small intestine
and colon were primarily of 6.7 kb, whereas both 6.7 and 8.9 kb bands were
expressed nearly equivalently in the other tissues. No NHE3 message was
detected in the human heart, lung, liver, skeletal muscle or pancreas.
Received 5 July 1994; accepted in final form 4 January 1995.
APS Manuscript Number C380-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.