Differences in the functional responses of two cell lines each expressing Pi-hydrolysis-coupled muscarinic receptors.
Fluorescent oxonol dyes were used to measure changes in the membrane potential of two different cell lines each expressing Pi-hydrolysis coupled muscarinic receptors. Both SK-N-SH human neuroblastoma cells and m1-transfected A9 L cells express muscarinic receptors which, when stimulated, elicit a large increase in intracellular calcium, and release of inositol phosphates. Despite the similarity in this second-messenger response, muscarinic stimulation resulted in a hyperpolarization in the transfected A9 L cells whereas a small depolarization was observed in the neuroblastoma cells. The carbachol-mediated hyperpolarization of the transfected A9 L cells could be mimicked by increasing intracellular calcium with the ionophore A23187, suggesting that it may be mediated by calcium-activated potassium channels. Exposure of SK-N-SH cells to A23187, on the other hand, had no effect on the membrane potential. These studies demonstrate that the activation of a second messenger system does not solely dictate the electrophysiological response of a cell, but that other factors such as the expression of ion-channels is critical in the determination of that response.
Baumgold
J
J
George Washington University Medical Center, Department of Pharmacology, Washington, D.C. 20037.
Paek
R
R
D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D006801:Humans; D006868:Hydrolysis; D007555:Isoxazoles; D008564:Membrane Potentials / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology; D011976:Receptors, Muscarinic / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D005456:Fluorescent Dyes; D007555:Isoxazoles; D011976:Receptors, Muscarinic; C018622:oxonol dyes (isoxazole); C049925:fura-2-am; D011493:Protein Kinase C; D002118:Calcium; D016257:Fura-2