ATP-sensitive potassium transport by pancreatic secretory granule membrane.
Electrolyte transport pathways in the pancreatic secretory granules may contribute to acini fluid production after fusion with the apical membrane. A component of this granule transport is a K(+)-selective pathway that has been measured indirectly by ionophore-induced lysis of the isolated secretory granules when suspended in a KCl solution. This granule membrane K+ transport was shown to be inhibited by physiological levels of ATP in a dose-dependent manner and was not reversed by ADP. The sulfonylurea tolbutamide (0.5 mM), a recognized inhibitor of ATP-sensitive K+ channels, also reduced the ionophore-dependent lysis by 46%. The ATP sensitivity of the K+ transport was influenced by pH (increased ATP sensitivity with decreasing pH) and KCl concentration (increased ATP sensitivity with increasing KCl). In addition, preincubation with phospholipase A2 (8.3 x 10(-10) g/ml) or lysophospholipids (6.7 x 10(-7) g/ml) produced a significant decrease in the granule K+ transport. However, it is not likely that this inhibition is due to a change in membrane fluidity, because fluidization with arachidonic acid or octanol did not have a comparable effect. The results then support a granule-associated K+ transport in pancreatic acinar cells and suggest that it is ATP and lysophospholipid sensitive.
Gasser
K W
KW
Department of Biological Sciences, Northern Illinois University, DeKalb 60115-2861.
Holda
J R
JR
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003594:Cytoplasmic Granules / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007476:Ionophores / Q000494:pharmacology; D008246:Lysophospholipids / Q000494:pharmacology; D008566:Membranes / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism*; D010741:Phospholipases A / Q000494:pharmacology; D054467:Phospholipases A2; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014044:Tolbutamide / Q000494:pharmacology
D007476:Ionophores; D008246:Lysophospholipids; D000255:Adenosine Triphosphate; D014044:Tolbutamide; D010741:Phospholipases A; D054467:Phospholipases A2; D011188:Potassium