Streptomycin and its analogues are potent inhibitors of the hypotonicity-induced Ca2+ entry and Cl- channel activity

Streptomycin is a common antibiotic used in culture media. It is also a known blocker of stretch-activated and mechanosensitive ion channels in neurons and cardiac myocytes. But very little information is available on its effect in the regulation of epithelial ion channels. Osmotic swelling is a kind of mechanical stretch. The opening of stretch-activated Ca2+ channels contributes to hypotonicity-induced Ca2+ influx which is necessary for the activation of volume-regulated Cl- channels in human cervical cancer cells. This study aimed to investigate the role of streptomycin in cell volume regulation. Treatment of cervical cancer SiHa cells with streptomycin and its analogues (gentamicin and netilmicin) did not affect the basal cytosolic Ca2+ ([Ca2+](i)) level. But it attenuated the hypotonicity-stimulated increase of [Ca2+](i) in a dose-dependent manner with halfmaximal inhibitory concentrations (IC50) of 25, 90 and 200 muM for streptomycin, gentamicin and netilmicin, respectively, when measured at room temperature. In contrast, under free extracellular Ca2+ condition, hypotonic stress only induced a small, progressive increase of [Ca2+](i), while 500 muM streptomycin did not affect this Ca2+ signaling. Streptomycin and its analogues (gentamicin and netilmicin) also inhibited the activation of volume-regulated Cl- channels in a dose-dependent manner with IC50 of 30, 95 and 250 muM at room temperature, respectively. Chronic culture with 50 muM streptomycin downregulates the activity of volume-regulated Cl- channels and retards the process of regulatory volume decrease in SiHa cells and MDCK cells. We suggest that using cells chronically cultured with streptomycin to study epithelial ion channels risks studying cellular and molecular pathology rather than physiology. (C) 2003 Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.