Development of chloride transport by the rat choroid plexus, in vitro.

The uptake and efflux of 36Cl in the lateral ventricle choroid plexus of 1-7-week-old rats were measured to determine if Cl transport changed with age and if such transport responded to inhibitors of CSF secretion and ion transport. The steady-state (30 min) Cl uptakes were 148 +/- 9.4 nmol.mg-1 dry weight at 1 week and 139 +/- 7.0 nmol.mg-1 dry weight at 7 weeks, (P > 0.05). The 36Cl efflux was significantly slower in 1 and 2 week plexuses compared to more mature tissues (P < 0.01) with k (rate coefficient) = 0.029 +/- 0.004 s-1, t1/2 = 24.1 +/- 3.3 s at 1 week and k = 0.041 +/- 0.003 s-1, t1/2 = 17.4 +/- 1.3 s at 7 weeks. 36Cl efflux at 1 week was unaffected by acetazolamide, bumetanide and DIDS (4,4 diisothiocyanato-stilbene-2,2 disulphonic acid), however, all these drugs substantially reduced efflux from 2, 3 and 7 week choroid plexuses. In contrast, the Cl conductance blocker, DPC (diphenylamine carboxylate) at 10(-4) M reduced 36Cl efflux from both 1 and 7 week tissues by 43% and 39%, respectively. These findings suggest that some transport systems responsible for movement of Cl out of the epithelium are either absent or less functional in the immature rat choroid plexus and may account for the relatively low level of CSF secretion in younger animals. The unidirectional efflux of 36Cl, J, was calculated for 1 week and adult rats, as a function of the choroid plexus volume to surface area ratio (V/A).(ABSTRACT TRUNCATED AT 250 WORDS)