Effects of nicotine on human nasal epithelium: evidence for nicotinic receptors in non-excitable cells

Abstract

 We investigated the effects of nicotine and its derivate nicotine di-d-tartrate on primary cultured human nasal epithelial cells. Both substances evoked an in-crease in the intracellular free calcium concentration. In the presence of extracellular Ca²⁺ the cytosolic Ca²⁺ ([Ca²⁺]_i) increase was long lasting, whereas in the absence of external Ca²⁺ there was a transient increase of [Ca²⁺]_i indicating that nicotine has an influence on Ca²⁺ conductances across the membranes and on intracellular Ca²⁺ stores. Both effects could be blocked by the nicotinic receptor antagonist methyllycaconitine (MLA). Apical or basolateral application of nicotine during transepithelial transport measurements with confluent monolayers of cultured human nasal cells resulted in a significant, reversible decrease of amiloride-sensitive sodium absorption with an apparent half-maximal blocker concentration of about 950 μM. To exclude the possibility that remnant neuronal components were responsible for the observed effects we used tetrodotoxin and verapamil to block putative neuronal channels and 4-(4-diethyla- mino)styryl-N-methylpyridinium iodide (4-di-2-Asp) to stain neuronal tissue. Both experimental approaches demonstrated that there were no neuronal-mediated effects. These results indicate the direct effects of nicotine on human nasal epithelium, giving the first evidence of the existence of nicotinic receptors in non-excitable cells.