Thrombin stimulation of Cl-/HCO3- exchange in human platelets

Functional interaction of carbonic anhydrase and chloride/bicarbonate exchange in human platelets

Recently, our laboratory has reported the presence of one acidifying Cl-/HC exchange mechanism in human platelets. This paper demonstrates that this exchanger decreases its activity after inhibition of carbonic anhydrase. BCECF-loaded platelets, previously equilibrated in a bicarbonate/CO2 buffered solution, were resuspended in a Hepes-buffered, chloride-free (glucuronate) medium to produce a pHi increase. After addition of 50 mM NaCl, pHi fell rapidly reaching steady state in the succeeding 400 s. The recovery in chloride-containing solution was in contrast to the effect of a similar change in osmolarity by addition of 50 mM sodium glucuronate that produced a significantly slower variation of pHi. Alkali loads produced by 25 mM TMA were also counteracted by HC equivalent efflux via Cl-/HC exchange. The present study shows that the efflux of HC was slower when the platelets were previously incubated in 100 microM methazolamide. As a conclusion, the recovery of pHi from alkalosis by Na-independent Cl-/HC exchange is facilitated in platelets by the enzymatic activity of the carbonic anhydrase.