cAMP stimulates the Na+-K+ pump in frog retinal pigment epithelium.
Adenosine 3', 5'-cyclic monophosphate (cAMP) induced increases in active Na+ secretion and K+ absorption that were blocked by apical ouabain (10(-4) M), suggesting stimulation of the Na+-K+ pump. cAMP also produced rapid membrane voltage and resistance changes that could be divided chronologically into three phases. In phase 1, the basolateral membrane depolarized at a faster rate than the apical membrane, probably as a result of an increase in basolateral membrane conductance. In phase 2, the apical membrane repolarized toward control faster than the basal membrane, whereas in phase 3 the basolateral membrane repolarized faster than the apical membrane. Apical ouabain completely inhibited the cAMP-induced repolarization of the apical membrane during phase 2. Thus the stimulation of the Na+-K+ pump occurs within minutes of cAMP elevation. Na+ removal from the basal side did not block the cAMP-induced voltage changes, indicating that the initial conductance increase is not due to Na+. In contrast, Na+ removal from the apical bath inhibited all phases of the cAMP response. This suggests that apical membrane Na+-dependent transport mechanisms mediate the stimulation of the Na+-K+ pump. cAMP also caused a significant drop in intracellular K+ activity (approximately 5 mM) that preceded phase 2. This drop could stimulate the Na+-K+ pump, as suggested by previous experiments.
D000818:Animals; D001692:Biological Transport; D002462:Cell Membrane / Q000502:physiology; D000242:Cyclic AMP / Q000494:pharmacology* / Q000502:physiology; D004594:Electrophysiology; D005260:Female; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D007552:Isotonic Solutions / Q000494:pharmacology; D008297:Male; D010857:Pigment Epithelium of Eye / Q000378:metabolism* / Q000648:ultrastructure; D011188:Potassium / Q000378:metabolism*; D011892:Rana catesbeiana; D000077331:Ringer's Solution; D012964:Sodium / Q000378:metabolism*; D013268:Stimulation, Chemical
D007473:Ion Channels; D007552:Isotonic Solutions; D000077331:Ringer's Solution; D012964:Sodium; D000242:Cyclic AMP; D011188:Potassium