Na+, K+, and Cl- transport in resting pancreatic acinar cells.
To understand the role of Na+, K+, and Cl- transporters in fluid and electrolyte secretion by pancreatic acinar cells, we studied the relationship between them in resting and stimulated cells. Measurements of [Cl-]i in resting cells showed that in HCO3(-)-buffered medium [Cl-]i and Cl- fluxes are dominated by the Cl-/HCO3- exchanger. In the absence of HCO3-, [Cl-]i is regulated by NaCl and NaK2Cl cotransport systems. Measurements of [Na+]i showed that the Na(+)-coupled Cl- transporters contributed to the regulation of [Na+]i, but the major Na+ influx pathway in resting pancreatic acinar cells is the Na+/H+ exchanger. 86Rb influx measurements revealed that > 95% of K+ influx is mediated by the Na+ pump and the NaK2Cl cotransporter. In resting cells, the two transporters appear to be coupled through [K+]i in that inhibition of either transporter had small effect on 86Rb uptake, but inhibition of both transporters largely prevented 86Rb uptake. Another form of coupling occurs between the Na+ influx transporters and the Na+ pump. Thus, inhibition of NaK2Cl cotransport increased Na+ influx by the Na+/H+ exchanger to fuel the Na+ pump. Similarly, inhibition of Na+/H+ exchange increased the activity of the NaK2Cl cotransporter. The combined measurements of [Na+]i and 86Rb influx indicate that the Na+/H+ exchanger contributes twice more than the NaK2Cl cotransporter and three times more than the NaCl cotransporter and a tetraethylammonium-sensitive channel to Na+ influx in resting cells. These findings were used to develop a model for the relationship between the transporters in resting pancreatic acinar cells.
Zhao
H
H
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235, USA.
Muallem
S
S
D000818:Animals; D001692:Biological Transport; D002034:Bumetanide / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism*; D017136:Ion Transport / Q000502:physiology; D010042:Ouabain / Q000494:pharmacology; D010179:Pancreas / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism*
D002712:Chlorides; D002034:Bumetanide; D010042:Ouabain; D012964:Sodium; D011188:Potassium