The effect of phorbol esters on human erythrocyte morphological discocyte-echinocyte transitions

12-O-Tetradecanoylphorbol-13-acetate (TPA) (100 nM) when incubated with human erythrocytes under conditions of ATP depletion, delayed the onset of the morphological transition from discocytes to echinocytes so that at 2 h, when control incubations were estimated to contain 65% echinocytes, those treated with TPA contained 23% echinocytes. TPA did not alter the subsequent rate of the transition which was complete by 3 h in control cells and 5 h in TPA-treated cells. Addition of 100 nM TPA to ATP-depleted erythrocytes at 2.5 h (greater than 80% echinocytes) for 0.5 h at 37 degrees C resulted in 17% reversal to a discocyte morphology, but as the time of incubation under conditions of ATP depletion was extended, the level of the reversal fell. TPA had no significant effect on the fall in ATP concentrations over the time course of the experiments (5 h). Preincubation of discocytes with TPA for 10 min also prevented, by approx. 50%, the echinocytosis induced by the calcium (0.2 mM) loading of discocytes using 5 microM A23187. TPA was unable to reverse the echinocyte morphology of calcium-loaded cells back to discocytes. The less potent tumour promotor 4-phorbol-12,13-didecanoate had no effect on this discocyte-echinocyte transition. Incubation of discocytes with the diacylglycerol 1-oleoyl-2-acetylglycerol (OAG) (1-10 microM) had complex effects on morphology, and the ATP-induced morphological transition, ranging from stomatocyte formation to echinocyte formation, depending upon the concentration of the agent and the time of incubation.