THE AMINOGLYCOSIDE G418 SUPPRESSES MUSCARINIC RECEPTOR-ACTIVATED CALCIUM-RELEASE IN STABLY TRANSFECTED MURINE N1E-115 NEUROBLASTOMA-CELLS

The aminoglycoside G418 inhibited the release of calcium (Ca2+) from internal stores coupled to muscarinic receptors in murine N1E-115 neuroblastoma cells carrying the aminoglycoside resistance gene neomycin phosphotransferase (NPT). No significant effect was observed on responses coupled to histamine or bradykinin receptors. Cells were transfected using the eukaryotic expression vector pH beta APr-1-neo and selected using G418. Two groups were differentiated either in the continued presence of G418 or in the absence of G418. Carbachol (1 mM), histamine (200 mu M) and bradykinin (100 nM) were administered to cells for thirty seconds and changes in [Ca2+](i) were measured with fluorescence video microscopy of single cells loaded with the Ca2+ indicator fura-2. The effects of G418 on carbachol evoked Ca2+ release included a 73% reduction in the number of cells responding, a two fold increase in the time to reach half-maximal response, a 35% reduction of the peak [Ca2+](i) in response to agonist and an elevation of resting [Ca2+](i) from 99 +/- 14 nM (mean +/- S.E.M.) to 155 +/- 27 nM. Acute application (20 min) of G418 to transfected cells differentiated without G418 also reduced the percentage of cells responding to carbachol. This effect was less pronounced in non-transfected parent cells. Thus, the mechanism might involve a metabolite of G418 produced in cells expressing NPT. These results indicate that G418 attenuates Ca2+ release coupled to muscarinic receptors.