Chloride channels in human platelets: evidence for activation by internal calcium.
Whole-cell patch-clamp recordings were made from freshly isolated human platelets. The pipette contained a high concentration of divalent cations, which permitted easy disruption of cell-attached membrane patches by suction. Single-channel currents were measured when the pipette contained isotonic BaCl2 or MgCl2 saline; over 30 sec -5 min an increasing number of channels appeared until conductance steps through individual channels could no longer be distinguished. The current-voltage relationship was curvilinear; chord conductance at -35 mV was 25 pS increasing to 45 to 52 pS at +45 mV. Ion substitution experiments showed the current to be primarily carried by Cl-. Erev was shifted 30 mV/10-fold change in external Cl- (replaced by gluconate), was similar with BaCl2 or MgCl2 in the pipette and was not significantly shifted by replacing external Na+ with K+. Addition of 1 mM BAPTA to the MgCl2 pipette saline prevented activation of Cl- currents; with isotonic CaCl2 internal saline, current appeared immediately upon patch rupture, suggesting that the Cl- channels are dependent on internal Ca2+. 5-nitro-2-(3-phenylpropylamino)-benzoate, reported to block a Cl- conductance in studies of rat epithelial cells, caused a potent flickery block and may be a useful tool with which to investigate the physiological role of Cl- currents in human platelets.
Mahaut-Smith
M P
MP
Physiological Laboratory, Cambridge, England.
D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D002712:Chlorides / Q000097:blood*; D004533:Egtazic Acid / Q000494:pharmacology / Q000031:analogs & derivatives; D004553:Electric Conductivity; D006801:Humans; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D009579:Nitrobenzoates / Q000494:pharmacology
D002712:Chlorides; D007473:Ion Channels; D009579:Nitrobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium