cAMP and protein kinase A stimulate acidification of rat liver endosomes in the absence of chloride.

Endosomes and lysosomes are acidified by an electrogenic proton pump in parallel with a chloride conductance and in kidney both of these may be regulated by cAMP. In vitro exposure of isolated rat liver endosomes to cAMP, PKA and GTP-gamma S stimulated acidification of "early" endosomes with or without C1-, but not in the absence of K+. cAMP and PKA also increased acidification rates of purified "late" endosomes, multivesicular bodies, CURL vesicles and lysosomes. "Early" endosomes prepared from livers perfused with cAMP also exhibited increased rates of acidification. cAMP and PKA had no consistent effects on steady-state intravesicular pH or proton efflux rates. Thus, acidification of several types of liver endocytic vesicles was stimulated by cAMP and PKA in the presence and absence of chloride, possibly due to changes in the proton pump itself and/or a cation conductance.