AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 1 77-R81, Copyright © 1986 by American Physiological Society
Neurohypophysial peptide potencies in cultured anuran epithelia (A6)
M. A. Lang, J. S. Handler and H. Gainer
To characterize the V2 receptor (for antidiuretic hormone), we have studied
the effect of a number of neurohypophysial hormone analogues on cyclic AMP
(cAMP) accumulation and short-circuit current in cultured epithelia formed
by A6 cells. A6 is the designation of a continuous cell line derived from
the kidney of Xenopus laevis. The order of potency for stimulating cAMP
accumulation and short-circuit current in A6 epithelia is like that for
stimulating water permeability in toad urinary bladder. As anticipated,
arginine vasotocin (AVT), the antidiuretic hormone of Amphibia, is more
potent than arginine vasopressin (AVP), the antidiuretic hormone of most
mammals. The two hormones differ only in the third amino acid (Phe-3 in AVP
is a substitution for Ile-3 in AVT). However, there are a number of
striking differences in the responsiveness of these amphibian V2 receptors
and mammalian V2 receptors to changes in the 7th, 8th, and 9th amino acids
where AVT and AVP are identical. 1) Substitution of Lys-8 for Arg-8 in AVP
results in marked loss of potency in Amphibia, whereas there is only modest
loss of potency in mammals. 2) Desglycinamide AVP is nearly as potent as
AVP in Amphibia, whereas it is inactive in mammals. 2) Tocinoic acid,
lacking amino acids 7, 8, and 9, has activity in Amphibia, but pressinoic
acid, lacking the same three amino acids, is inactive.
