Mechanisms of inhibition of CaV3.1 T-type calcium current by aliphatic alcohols

Abstract

Many aliphatic alcohols modulate activity of various ion channels involved in sensory processing and also exhibit anesthetic capacity in vivo. Although the interaction of one such compound, 1-octanol (octanol) with different T-type calcium channels (T-channels) has been described, the mechanisms of current modulation and its functional significance are not well studied. Using patch-clamp technique, we investigated the mechanisms of inhibition of T-currents by a series of aliphatic alcohols in recombinant human Ca V 3.1 (α1G) T-channel isoform expressed in human embryonic kidney (HEK) 293 cells and thalamocortical (TC) relay neurons in brain slices of young rats. Octanol, 1-heptanol (heptanol) and 1-hexanol (hexanol) inhibited the recombinant Ca V 3.1 currents in concentration-dependent manner yielding IC 50 values of 362 µM, 1063 µM and 3167 µM, respectively. Octanol similarly inhibited native thalamic Ca V 3.1 T-currents with an IC 50 of 287 µM and diminished burst firing without significant effect on passive membrane properties of these neurons. Inhibitory effect of octanol on T-currents in both native and recombinant cells was accompanied with accelerated macroscopic inactivation kinetics and hyperpolarizing shift in the steady-state inactivation curve. Additionally, octanol induced a depolarizing shift in steady-state activation curves of T-current in TC neurons. Surprisingly, the recovery from fast inactivation at hyperpolarized membrane potentials was accelerated by octanol up three-fold in native but not recombinant channels. Given the importance of thalamocortical pathways in providing sleep, arousal, and anesthetic states, modulation of thalamic T-currents may at least contribute to the pharmacological effects of aliphatic alcohols.

Inhibition of T-type calcium current in rat thalamocortical neurons by isoflurane

“…Surprisingly, we found that IFL did not affect resting membrane potential and input resistance. These findings are in line with the previously reported inhibitory effect of another anesthetic, aliphatic alcohol octanol, on T-current, along with unchanged passive membrane properties in TC neurons (Eckle and Todorovic 2010). A possible explanation of these divergent findings between our and Puil’s group is not immediately obvious, but some possibilities include: internal biological variability within the rat phenotypes; different environmental, nutritional, and housing conditions; and a possible difference in the recording conditions.…”

“…Transitions from closed to inactivated states can be measured using long conditioning prepulses at varying potentials, producing what are commonly referred to as steady-state inactivation curves. We assessed steady-state inactivation curves using our standard double-pulse protocol with 3.5-s long prepulses to variable voltages (from −110 to −50 mV in 5-mV increments) and V t to −50 mV (Eckle and Todorovic 2010). The two panels of Figure 3A show representative traces of the currents in the same TC cell before the application of IFL (control, left) and after 10 min of application of 2 vol% of IFL (right).…”

“…8023, revised 2002). Our in vitro slice preparation technique has been described previously (Eckle and Todorovic 2010). Briefly, young Sprague-Dawley rats of either sex (postnatal days 8–15) were briefly anesthetized with isoflurane and decapitated.…”

Bidirectional plasticity in the primate inferior olive induced by chronic ethanol intoxication and sustained abstinence

“…Ca V 3.1 channels are largely inactive at resting potential and recover from inactivation in both a time-and voltage-dependent manner. Both 10 and 100 mM ethanol accelerated the recovery from inactivation, similar to the effect of long-chain alcohols (20). Because the voltage-dependence of inactivation was not affected and the deinactivation kinetics were not slowed, the decrease in I T must have been due to a decrease in conductance and/or number of available channels.…”

“…In addition, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels that conduct I h also facilitate rebound firing in IO neurons (18). In rodents, I T was inhibited acutely by ethanol and long-chain aliphatic alcohols (19,20), whereas I h was augmented by ethanol (21). Recent studies demonstrated that the tremor mediated by the IO requires Ca V 3.1 T-type calcium channels (22,23) and is synchronized by gap junctions (24).…”