IL-1 activates the Na⁺/H⁺ antiport in a murine T cell

One of the early events following growth factor exposure is elevation of intracellular pH, a process mediated by the Na⁺/H⁺ antiport. We studied the effects of human rIL-1α (HrIL-1α) on intracellular pH (pHi) and calcium ([Ca²⁺](i)) in a murine T cell line (MD10 cells), which proliferates in response to IL-1 alone. By using the intracellularly trapped fluorescent dyes (2¹,7¹-bis-2-carboxyethyl)-5(and -6) carboxyfluorescein) and indo-1, we monitored immediate to early changes of pHi and [Ca²⁺](i) in response to HrIL-1α. Exposure to HrIL-1α (120 pM) leads to an early, sustained intracellular alkalinization (ΔpH = + 0.09 ± 0.03) that plateaus within 20 min. Lower concentrations of the monokine (12 pM, 1.2 pM) have a positive but not statistically significant effect on pHi. These effects parallel the degree of MD10 IL-1R saturation predicted by the K(D) (49 pM) as assessed by ¹²⁵I-HrIL-1α binding by MD10 cells (B(max) = ~1300). Both the MD10 IL-1 receptor K(D) and the HrIL-1α concentration required to induce early measurable alkaline pH shifts, however, exceed by three orders of magnitude the HrIL-1α ED₅₀ (50 fM) required for MD10 proliferation. The IL-1-induced rise in pHi is both sodium dependent and amiloride sensitive, indicative of activation of the Na⁺/H⁺ antiport. Additionally, PMA (100 nM) and IL-2 (2 nM) alkalinize MD10 cells, with the rise in pHi as a result of PMA exceeding the maximal IL-1 effect (Δ pH = + 0.13 ± 0.04). Furthermore, although PMA alkalinizes cells previously exposed to HrIL-1α, the monokine does not alter the pHi of PMA-treated MD10 cells. Importantly, intracellular alkalinization induced by either HrIL-1α or PMA is inhibited by staurosporine (1 μiM). Finally, HrIL-1α does not change MD10 [Ca²⁺](i), in either an acute or sustained fashion. These results indicate that IL-1 activates the Na⁺/H⁺ antiport in T cells by a mechanism that is unrelated to changes in [Ca²⁺](i) but may involve protein kinase C activation.