Effects of phorbol 12-myristate 13-acetate on potassium transport in the red blood cells of frog Rana temporaria

Phorbol 12-myristate 13-acetate (PMA), a stimulator of PKC, was examined for its influence on K+ (Rb-86) influx in the frog erythrocyte. PMA, 0.1 mu M, was found to accelerate ouabain-sensitive K+ influx, which was suppressed by 73% with 1 mM amiloride, indicating secondary activation of the Na+-K+-pump due to stimulation of Na+ /H+ exchange. PMA-induced stimulation of the sodium pump was completely inhibited with 1 mu M staurosporine and by similar to 50% with 20 mu M chelerythrine. In contrast to Na+-K+-pump, an activity of Cl--dependent K+ transport (K-Cl cotransport, KCC), calculated as the difference between K+ influxes in Cl- and NO3 (-)-media, was substantially decreased under the influence of PMA. Staurosporine fully restored the PMA-induced inhibition of KCC, whereas chelerythrine did not exert any influence. Osmotic swelling of the frog erythrocytes was accompanied by approximately twofold stimulation of KCC. Swelling-activated KCC was inhibited by similar to 50 and similar to 83% in the presence of PMA and genistein, respectively, but not chelerythrine. Exposure of the frog erythrocytes to 5 mM fluoride (F-) also reduced the KCC activity in isotonic and hypotonic media, with maximal suppression of K+ influx in both media being observed upon simultaneous addition of PMA and F-. Furosemide and [(dihydronindenyl)oxy] alkanoic acid inhibited the K+ influx in both the media by similar to 50-60%. The results obtained show both the direct and indirect effects of PMA on the K+ transport in frog erythrocytes and a complicated picture of KCC regulation in frog erythrocytes with involvement of PKC, tyrosine kinase and protein phosphatase.