Carbachol-induced increase of Na+/H+ antiport and recruitment of Na+,K(+)-ATPase in rabbit lacrimal acini.
Parallel arrays of Na+/H+ and Cl-/HCO3- antiporters are believed to catalyze the first step of transepithelial electrolyte secretion in lacrimal glands by coupling Na+ and Cl- influxes across acinar cell basolateral membranes. Tracer uptake methods were used to confirm the presence of Na+/H+ antiport activity in membrane vesicles isolated from rabbit lacrimal gland fragments. Outwardly-directed H+ gradients accelerated 22Na+ uptake, and amiloride inhibited 96% of the H+ gradient-dependent 22Na+ flux. Amiloride-sensitive 22Na+ influx was half-maximal at an extravesicular Na+ concentration of 14 mM. In vitro stimulation of isolated lacrimal acini with 10 microM carbachol for 30 min increased Na+/H+ antiport activity of a subsequently isolated basolateral membrane sample 2.5-fold, but it did not significantly affect Na+/H+ antiport activity measured in intracellular membrane samples. The same treatment increased basolateral membrane Na+,K(+)-ATPase activity 1.4-fold; this increase could be accounted for by decreases in the Na+,K(+)-ATPase activities of intracellular membranes. Thus, it appears that cholinergic stimulation causes recruitment of additional Na+,K(+)-ATPase pump units to the acinar cell basolateral plasma membrane. The mechanistic basis of the increase in basolateral membrane Na+/H+ antiport activity remains unclear.
Department of Physiology and Biophysics, University of Southern California School of Medicine, Los Angeles 90033.
R W
RW
Lambert
C A
CA
Maves
A K
AK
Mircheff
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects; D002499:Centrifugation, Density Gradient; D007765:Lacrimal Apparatus / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000037:antagonists & inhibitors / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013347:Subcellular Fractions
D002352:Carrier Proteins; D008565:Membrane Proteins; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; D002217:Carbachol; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase