CHARACTERIZATION OF ZINC UPTAKE AND ITS REGULATION BY ARACHIDONIC-ACID IN FETAL TYPE-II PNEUMOCYTES

In freshly isolated fetal guinea pig type II pneumocytes, zinc uptake is time and temperature dependent. Two pathways of uptake exist, resul ting in a rapid phase that reaches a steady state within 30 s and a sl ower linear phase that does not attain a steady state within 60 min. B oth processes exhibit saturation kinetics. The rapid phase has a maxim al zinc uptake of 60.7 +/- 9.3 pmol . 10(6) cells(-1). 30 s(-1) and an apparent affinity (K-t) of 13.7 +/- 5.4 mu M. The maximum velocity of uptake (V-max) of the slower phase is 24.6 +/-: 1.9 pmol . 10(6) cell s(-1) min(-1) with a K-t of 22.0 +/- 3.6 mu M. Epinephrine, terbutalin e, dibutyryl adenosine 3',5'-cyclic monophosphate, and dexamethasone h ave no significant effect on zinc uptake, while arachidonic acid (AA) stimulates. Dose-response data of AA-stimulated zinc uptake gives an a pparent K-0.5 Of 0.42 +/- 0.01 mu M and a Hill coefficient of 1. The m aximal uptake in the rapid phase is significantly increased to 146.8 /- 12.4 pmol . 10(6) cells(-1) 30 s(-1) and in the slow phase, the V-m ax for zinc uptake is also significantly increased to 33.0 +/- 1.8 pmo l . 10(6) cells(-1) min(-1) by 10 mu M AA. However, the K-t values in both processes remain unchanged after AA stimulation. The effect is no t mediated by either leukotrienes or prostaglandins but can be mimicke d by other unsaturated fatty acids.