Received for publication June 8, 2005.
Revised September 15, 2005.
Accepted for publication September 16, 2005.

Tobacco Smoke Chemicals Attenuate Brain-to-Blood Potassium Transport Mediated by the Na,K,2Cl-Cotransporter During Hypoxia-Reoxygenation

Abstract

Smoking tobacco, including cigarettes, has been associated with an increased incidence and relative risk for cerebral infarction in both men and women. Recently, we have shown that nicotine and cotinine attenuate abluminal (brain facing) K⁺ uptake mediated by the Na,K,2Cl-cotransporter (NKCC) in bovine brain microvessel endothelial cells (BBMECs) after hypoxic/aglycemic exposure (stroke conditions). The purpose of the current study was to explore the effects of nicotine and tobacco smoke chemicals on K⁺ movement through the blood-brain barrier during both hypoxia/aglycemia and reoxygenation. BBMECs were exposed to nicotine/cotinine, nicotine-containing cigarette smoke extract (N-CSE), or nicotine-free cigarette smoke extract (NF-CSE) in quantities designed to mimic plasma concentrations of smokers. Stroke conditions were mimicked in vitro in BBMECs through 6 hr hypoxia/aglycemia with or without 12 hr reoxygenation, after which NKCC-mediated K⁺ uptake and paracellular integrity were measured with ⁸⁶Rb and ¹⁴C-sucrose, respectively. In addition, K⁺ concentrations in brain extracellular fluid were estimated in ⁸⁶Rb injected rats that were administered nicotine, N-CSE, or NF-CSE and on whom global ischemia/reperfusion by in vivo four vessel occlusion was performed. Both in vitro and in vivo paradigms showed nicotine, the major alkaloid present in tobacco smoke, to be the determining factor of an inhibited response of abluminal NKCC in BBMECs during and after stroke conditions. This was measured as a decrease in abluminal brain endothelial cell NKCC activity, and as an increase in brain extracellular K⁺ concentration measured as the brain extracellular fluid ⁸⁶ Rb-to-plasma ratio after in vivo four vessel occlusion with reperfusion.

Key words: Blood-Brain Barrier, Na, K, 2Cl-cotransporter, cigarette smoke extract, nicotine, potassium, stroke