Abstract
Brain penetration of clonidine, an alpha-2 adrenoceptor agonist, was studied using an in vitro cell culture system consisting of primary cultures of porcine brain capillary endothelial cells. Uptake of clonidine was measured as a function of its concentration in the incubation mixture. Saturation of uptake was apparent and could be described by Michaelis-Menten-type kinetics (K M = 1.34 mM;V max = 0.099 nmol/min/cm2). Saturation was not observed at a low temperature (4°C). Transendothelial transport experiments revealed that translocation of clonidine cannot be attributed solely to paracellular leakage. Uptake was reduced at low extracellular pH or by using an incubation buffer that contained the K+ionophore valinomycin. Time-dependent uptake of clonidine and transendothelial transport were slower than expected considering the high octanol-to-buffer partition coefficient of this compound. On the basis of transendothelial transport experiments, we concluded that the carrier system responsible for active transport of clonidine is located at both the apical and the basolateral membrane domain.
Footnotes
-
Send reprint requests to: Dr. J. Huwyler, University Hospital, Department of Anesthesia and Research, Hebelstrasse 20, CH-4031 Basel, Switzerland. E-mail:Huwylerj{at}ubaclu.unibas.ch
-
↵1 This work was supported by Swiss National Science Foundation Grant 32–42179.94.
- Abbreviations:
- DMSO
- dimethylsulfoxide
- MEM
- minimum essential medium
- Papp
- coefficient of permeability
- HEPES
- 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid
- Received October 15, 1996.
- Accepted March 3, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|