Expression of a rapid, low-voltage threshold K current in insulin-secreting cells is dependent on intracellular calcium buffering.
Depolarization-activated outward currents ranging in amplitude from 100-1000 pA were studied in cultured, insulin-secreting HIT cells and mouse B-cells using the whole-cell patch clamp. Outward current was identified as a K current since it was blocked by K channel blockers and its tail current reversed near EK. The K currents of HIT cells dialyzed with internal solutions containing 0.1-10 mM EGTA with no added calcium (Ca), or 10 mM EGTA with 2 mM added Ca, activated rapidly with depolarization. However, the stronger Ca buffer BAPTA (5 mM; no added Ca) blocked the rapidly activating current to reveal an underlying more slowly activating K current. With intracellular EGTA, application of the Ca channel blocker cadmium mimicked the effect of intracellular BAPTA. These data suggest that the rapid K current was mediated by low-voltage threshold, Ca-activated K channels while the slower K current was mediated by high threshold delayed rectifier K channels. Mouse B-cells also had both K current components. Dialyzing these cells with either BAPTA (5 mM, no added Ca) or high EGTA (10 mM with 2 mM Ca) blocked the rapid Ca-activated K current observed when cells were filled with 0.1 to 1 mM EGTA. It is concluded that the extent of Ca-activated K current activation in either HIT or adult mouse B-cells depends on the degree of intracellular Ca buffering.
Satin
L S
LS
Department of Physiology, University of Washington, School of Medicine, Seattle.
Hopkins
W F
WF
Fatherazi
S
S
Cook
D L
DL
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism; D002104:Cadmium; D002118:Calcium / Q000502:physiology*; D002478:Cells, Cultured; D003956:Dialysis; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D005260:Female; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D008564:Membrane Potentials; D051379:Mice; D015221:Potassium Channels / Q000378:metabolism*
D007328:Insulin; D015221:Potassium Channels; D002104:Cadmium; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium