Mf. Leite et al., REGULATION OF ANP SECRETION BY ENDOTHELIN-1 IN CULTURED ATRIAL MYOCYTES - DESENSITIZATION AND RECEPTOR SUBTYPE, American journal of physiology. Heart and circulatory physiology, 36(6), 1994, pp. 80002193-80002203
We examined endothelin-1 (ET-1) binding and ET-1-regulated atrial natr
iuretic peptide (ANP) secretion in primary cultures of adult rat atria
l myocytes. ET-1 binding was analyzed as a reversible bimolecular reac
tion, with bimolecular association rate constant = 1.9 x 10(9) M(-1).h
(-1), dissociation rate constant = 0.028 h(-1), and a dissociation con
stant, calculated from these values = 0.015 nM. ET-1 increased ANP sec
retion with a one-half effective concentration (EC(50)) of 0.62 nM, wh
ich correlated with EC(50) receptor occupancy under equivalent experim
ental conditions (0.75 nM). The secretory response rapidly desensitize
d (half-time = 10 min at 10 nM ET-1). The time courses for ET-1 bindin
g, ET-1-stimulated secretion, and desensitization were all comparable.
Recovery from desensitization was slow and paralleled the recovery of
I-125-labeled ET-1 binding. The ET(A) receptor subtype-selective anta
gonist, BQ-123, inhibited I-125-ET-1 binding and ET-1-activated ANP se
cretion with high affinity, whereas the ET(B)-selective agonists, endo
thelin-3 and sarafotoxin S6c, inhibited binding with low affinity and
did not effectively stimulate ANP secretion. We conclude that 1) ET-1
can stimulate ANP secretion by direct action on the atrial myocytes; 2
) primary cultures of adult rat atrial myocytes express only the ET(A)
receptor subtype; 3) the ANP secretory response to ET-1 desensitizes
rapidly but recovers slowly; and 4) occupation of the ET(A) receptors
by ET-1 initiates the unidirectional sequence of receptor activation,
signal transduction, ANP secretion, and finally, desensitization.