Cross-talk between ATP-regulated K+ channels and Na+ transport via cellular metabolism in frog skin principal cells.
Isolated frog skin epithelium, mounted in an Ussing chamber and bathed in standard NaCl Ringer solution, recycles K+ across the basolateral membrane of principal cells through an inward-rectifier K+ channel (Kir) operating in parallel with a Na+-K+-ATPase pump. Here we report on the metabolic control of the Kir channel using patch clamping, short-circuit current measurement and enzymatic determination of cellular (ATP (ATPi). 2. The constitutively active Kir channel in the basolateral membrane has the characteristics of an ATP-regulated K+ channel and is now classed as a KATP channel. In excised inside-out patches the open probability (Po) of KATP channels was reduced by ATPi with half-maximum inhibition at an ATPi concentration of 50 microM. 3. ATPi measured (under normal Na+ transport conditions) with luciferin-luciferase was 1.50 +/- 0.23 mM (mean +/- S.E.M.; range, 0.4-3.3 mM n = 11). Thus the KATP channel would be expected to be inactive in intact cells if ATPi was the sole regulator of channel activity. KATP channels which were inactivated by 1 mM ATPi in excised patches could be reactivated by addition of 100 microM ADP on the cytosolic side. When added alone, ADP blocks this channel with half-maximal inhibition at [ADPi] > 5 mM. 4. Sulphonylureas inhibit single KATP channels in cell-attached patches as well as the total basolateral K+ current measured in frog skin epithelia perforated with nystatin on the apical side. 5. Na+-K+-ATPase activity is a major determinant of cytosolic ATP. Blocking the pump activity with ouabain produced a time-dependent increase in ATPi and reduced the open probability of KATP channels in cell-attached membranes. 6. We conclude that the ratio of ATP/ADP is an important metabolic coupling factor between the rate of Na+-K+ pumping and K+ recycling.
Urbach
V
V
Department of Physiology, University College, Cork, Ireland.
Van Kerkhove
E
E
Maguire
D
D
Harvey
B J
BJ
D000244:Adenosine Diphosphate / Q000378:metabolism / Q000502:physiology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D003847:Deoxyglucose / Q000494:pharmacology; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology*; D011893:Rana esculenta; D011896:Rana temporaria; D012867:Skin / Q000166:cytology / Q000378:metabolism; D012879:Skin Physiological Phenomena; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism
D000963:Antimetabolites; D004791:Enzyme Inhibitors; D015221:Potassium Channels; D010042:Ouabain; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003847:Deoxyglucose; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase