Voltage-gated potassium channels and the control of membrane potential in human platelets.
1. Human platelets were studied using a combination of patch-clamp and fluorescent indicators of membrane potential and [Ca2+]i. 2. Whole-cell and cell-attached patch recordings showed voltage-gated channels selective for K+ (IK(V]. These channels were activated by depolarization at a threshold close to the platelet resting potential and were blocked by the venom charybdotoxin (CTX; 10-20 nM). Several different conductance states were observed, ranging from 5 to 34 pS, with isotonic KCl in the patch pipette and bath. 3. Measurements with the potential-sensitive dye 3,3'-dipropylthia-dicarbocyanine, diS-C3-(5), in platelet suspensions showed that CTX depolarized the resting potential by approximately 25 mV. Thus, CTX-sensitive, voltage-gated K+ channels appear to play a major part in setting the resting potential. 4. ADP-evoked Ca2+ influx, monitored with Fura-2, was reduced by 10 nM-CTX. Restoration of a large negative membrane potential with valinomycin reversed this effect of CTX. These results suggest that the Ca2+ influx depends on the negative membrane potential and that K+ channels may be important in maintaining this potential during activation.
Mahaut-Smith
M P
MP
Physiological Laboratory, University of Cambridge.
Rink
T J
TJ
Collins
S C
SC
Sage
S O
SO
D001792:Blood Platelets / Q000502:physiology*; D002118:Calcium / Q000097:blood; D018999:Charybdotoxin; D004553:Electric Conductivity / Q000187:drug effects; D006801:Humans; D015640:Ion Channel Gating; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D012604:Scorpion Venoms / Q000494:pharmacology
D015221:Potassium Channels; D012604:Scorpion Venoms; D018999:Charybdotoxin; D002118:Calcium