Functional properties and cell type specific distribution of I h channels in leech neurons

Abstract

The hyperpolarisation-activated cation current (I h) has been described in many vertebrate and invertebrate species and cell types. In neurons, I h is involved in rhythmogenesis, membrane potential stabilisation and many other functions. In this work, we investigate the distribution and functional properties of I h in identified leech neurons of intact segmental ganglia. We found I h in the mechanosensory touch (T), pressure (P) and noxious (N) neurons, as well as in Retzius neurons. The current displayed its largest amplitude in P neurons and we investigated its biophysical and pharmacological properties in these cells. I h was halfmaximally activated at-65 mV and fully activated at-100 mV. The current mutually depended on both Na + and K + with a permeability ratio p na/p k of ∼0.21. The reversal potential was approximately-35 mV. The time course of activation could be approximated by a single time constant of ∼370ms at-60 mV, but required two time constants at-80 mV of ∼80 and ∼560ms. The current was half-maximally blocked by 0.3mmol l -1Cs + but was insensitive to the bradycardic agent ZD7288. The physiological function of this channel could be a subtle alteration of the firing behaviour of mechanosensory neurons as well as a stabilisation of the resting membrane potential. © 2012. Published by The Company of Biologists Ltd.