The Journal of Neurophysiology Vol. 82 No. 3 September 1999, pp. 1627-1631
Copyright ©1999 by the American Physiological Society

RAPID COMMUNICATION

TGF1 Regulates the Gating Properties of Intermediate-Conductance K_Ca Channels in Developing Parasympathetic Neurons

Department of Biology and Biochemistry, University of Houston, Houston, Texas 77204-5513

Lhuillier, Loic and Stuart E. Dryer. TGF1 Regulates the Gating Properties of Intermediate-Conductance K_Ca Channels in Developing Parasympathetic Neurons. J. Neurophysiol. 82: 1627-1631, 1999. The developmental expression of Ca²⁺-activated K⁺ channels (K_Ca) in chick ciliary ganglion (CG) neurons is regulated by a target-derived avian isoform of TGF1, which evokes a robust increase in the number of functional large-conductance (BK) K_Ca channels but which produces no change in their kinetics. However, CG neurons express multiple K_Ca channel subtypes. Here we show that TGF1 regulates the gating properties of intermediate-conductance (IK) K_Ca channels in developing CG neurons. IK channels in inside-out patches excised from control E9 CG neurons became active on exposure to 1-5 µM free Ca²⁺ but then remained active on return to Ca²⁺-free salines. In contrast, IK channels in TGF1-treated cells became active on exposure to 1-5 µM Ca²⁺, but became quiescent immediately on return to Ca²⁺-free salines. In contrast to its effects on BK channels, TGF1 had no effect on the mean number of IK channels detected in excised patches. IK channels were not activated in cell-attached patches on E9 neurons depolarized by bath application of 145 mM KCl in the presence of 5 mM external Ca²⁺. However, BK channels were activated immediately by this procedure and were detected at a higher density in TGF1-treated cells. In addition, analyses of macroscopic K_Ca fluctuations, and the voltage-dependence of K_Ca tail currents, suggest that IK channels do not contribute to voltage-evoked whole cell K_Ca. IK channels therefore may have some other function. These results indicate that the effects of TGF1 on CG neurons entail distinct actions on multiple K_Ca channel subtypes.