Abstract:

The effect of sphingosylphosphorylcholine (SphPCho) on the intracellular pH (pH_i) in GH₄C₁ cells was investigated. SphPCho evoked a very slow increase in basal pH_i. In cells acidified with nigericin, SphPCho induced a rapid alkalinization of the cells. The effect was inhibited in a Na⁺-free buffer solution, but was insensitive to ethylisopropyl amiloride, a potent inhibitor of Na⁺-H⁺ exchangers (NHE). Reverse transcription and PCR showed that the predominant isoform of the antiport expressed in GH₄C₁, cells is NHE-1. The rate of alkalinization after stimulation with propionate, and after addition of Na¹ to cells acidified with NH₄Cl, was enhanced in cells treated with SphPCho. The initial rate of alkalinization after addition of Na⁺ to acidified cells treated with SphPCho gave an apparent K_m value of 15 ± 2 mM for Na⁺. The V_max value was 9 ± 22 mM H⁺/min. The effect was insensitive to ouabain, staurosporine and bafilomycin A. However, the SphPCho-evoked alkalinization was abolished in cells treated with 2-deoxy-D-glucose. The effect was not due to the charge of the molecule, as stearylamine increased pH_i in Na⁺-containing and Na⁺-free buffer. The results show that SphPCho may activate Na⁺-H⁺ exchange, and that this effect is mediated via an amiloride-insensitive exchange mechanism.

Keywords: pituitary; lipid; Na+-H+ exchange; sphingosine derivative; intracellular pH

Document Type: Research article

DOI: 10.1111/j.1432-1033.1997.00394.x

Affiliations: 1: Department of Biosciences, Division of Animal Physiology, University of Helsinki, Finland 2: Division of Cell Biology, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada