AJP - Cell Physiology, Vol 253, Issue 6 C774-C782, Copyright © 1987 by American Physiological Society
[3H]protein secretion in rat parotid gland: substance P-beta-adrenergic synergism
C. Dreux, V. Imhoff and B. Rossignol
Laboratoire de Biochimie des Transports Cellulaires, Universite Paris-Sud, Orsay, France.
In parotid fragment [3H]protein, secretion induced by substance P was
moderate, but strongly Ca dependent. However, secretion induced by
isoproterenol was large and Ca independent. Potentiation of protein
secretion was observed when substance P (SP) and isoproterenol (ISO) acted
together. Addition of 10(-8) M SP caused a shift to the left in the
secretion dose-response curve caused by ISO, but did not enhance
ISO-induced maximal response. The potentiating effect seems to be a
postreceptor event, since it can be mimicked by forskolin (FK), known to
induce directly cAMP accumulation, thus bypassing the beta-adrenergic
receptor. The synergism described above was, therefore, investigated at the
second messenger production level. Stimulation of parotid gland fragments
by simultaneous addition of SP plus ISO or FK did not modify cAMP nor
inositol trisphosphate (IP3) accumulation induced independently by each
secretagogue alone. The ionophore A23187 was also able to potentiate
secretion induced by a beta-adrenergic agonist, this effect being totally
abolished by external calcium omission, thus suggesting a role for external
calcium in this potentiation phenomenon. These results suggest that the
potentiation phenomenon observed is a postreceptor event that occurs at a
step distal from the second messenger production.
