Differential regulation of potassium currents by FGF-1 and FGF-2 in embryonic Xenopus laevis myocytes
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 512, Issue 1, pages 109–118, October 1998
How to Cite
Chauhan-Patel, R. and Spruce, A. E. (1998), Differential regulation of potassium currents by FGF-1 and FGF-2 in embryonic Xenopus laevis myocytes. The Journal of Physiology, 512: 109–118. doi: 10.1111/j.1469-7793.1998.109bf.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 1 May 1998; accepted after revision 17 June 1998.)
- 1Fibroblast growth factors (FGFs) are involved in the regulation of many aspects of muscle development. This study investigated their role in regulating voltage-dependent K+ currents in differentiating Xenopus laevis myocytes. Both FGF-1 and FGF-2 are expressed by developing muscle cells, so their actions were compared. Experiments were performed on cultured myocytes isolated from stage 15 embryos.
- 2Long-term exposure of the embryonic myocytes to FGF-1 downregulated inward rectifier K+ current (IK(IR)) density as well as both sustained and inactivating voltage-dependent outward K+ currents (IK,S and IK,I, respectively) and their densities. In contrast, FGF-2 upregulated these currents, although, because of an increase in capacitance caused by FGF-2, current density did not change with this factor.
- 3The regulation of IK(IR) by FGF-1 was prevented by the cytoplasmic tyrosine kinase inhibitor herbimycin A, but that of IK,S and IK,I was unaffected, indicating that FGF-1 achieves its regulatory effects on electrical development via separate signalling pathways. The receptor tyrosine kinase inhibitor genistein in isolation suppressed K+ currents, but this may have occurred through a channel-blocking mechanism.
- 4In many cells, IK,S was found to be composed of two components with differing voltage dependencies of activation. The FGFs brought about an alteration in the amount of total IK,S by equal effects on each component. Conversely, herbimycin A increased the proportion of low voltage-activated current without affecting total current amplitude. Therefore, we suggest that a single species of channel whose voltage dependence is shifted by tyrosine phosphorylation generates IK,S.
- 5In summary, FGF-1 and FGF-2 exert opposite effects on voltage-dependent K+ currents in embryonic myocytes and, furthermore, FGF-1 achieves its effects on different K+ currents via separate second messenger pathways.