We have recently found that mouse megakaryocytes responded to extracellular alkalinization to pH>8.0, generating a K
+ current under voltage-clamped conditions with the whole cell recording mode of the patch-clamp technique. The purpose of this study was to physiologically and pharmacologically characterize the alkaline-dependent K
+ conductance of the megakaryocyte membrane. The alkalinization-induced K
+ current (I
ALK) did not seem to be Ca
2+-dependent since I
ALK was allowed to be generated under intracellularly Ca
2+-buffered conditions with 10 mM EGTA, which completely prevented the generation of caffeine-induced Ca
2+-activated currents of mouse megakaryocytes; and no [Ca
2+]
i elevation was evoked by the alkalinization protocol in contrast to a significant increase in [Ca
2+]
i in response to caffeine when [Ca
2+]
i was measured with a fura 2 ratiometry. I
ALK was strongly suppressed with tetraethylammonium (TEA), 4-aminopyridine (4-AP) and streptomycin (SM), but was completely resistant to quinidine (QND). The values of IC
50 for the suppression of I
ALK with TEA, 4-AP and SM were 5.6, 0.47 and 1.5 mM, respectively. Voltage-gated K
+ currents (I
K) of the same megakaryocyte preparation were weakly suppressed with TEA and 4-AP, while they were significantly suppressed with either SM or QND. These results suggest that mouse megakaryocytes possess K
+ conductance that was activated by extracellular alkalinization and that probably differs from conventional K
+ conductance in its pharmacological properties.
View full abstract