Fig. 2

T-type channels are specifically upregulated in the caps⁻lpH⁺ neurons of longer-term diabetic rats without changes in their biophysical properties. a Representative traces of Ba²⁺ current recorded in the caps⁻lpH⁺ neurons of control and diabetic rats. Currents were evoked by a depolarization step from a holding potential of −100 to −50 mV. b Diabetes-induced upregulation of T-type channels is revealed at the plot of the transient current density, TCD, versus a depolarizing voltage step in the activation protocol. An insert demonstrates TCD amplitude for each tested neuron and their mean values (boxes) with standard errors (upper whiskers) in the control (c) and diabetic (d) neurons at a depolarization step to −50 mV. c HVA currents were not changed under diabetic conditions as revealed at the plot of persistent Ba²⁺ current versus depolarizing step in the activation protocol. The averaged value of Ba²⁺ current during last 10 ms of depolarization step was taken as a persistent current amplitude. Current densities are not significantly different between diabetes and control in a range of voltage steps from −30 to 0 mV where HVA currents are main contributors to the persistent current (p > 0.05). An insert demonstrates persistent current density amplitude for each tested neuron and their mean values (boxes) with standard errors (upper whiskers) in the control (c) and diabetic (d) neurons at a depolarization step to −20 mV. d Biophysical properties of T-type channels of the caps⁻lpH⁺ neurons are not changed in longer-term diabetes. Inactivation of normalized transient current (left curves) calculated for experimental results depicted in E; activation of normalized transient current conductance (right curves) for the experimental results depicted in B. e Diabetes-induced upregulation of T-type channels is revealed in a voltage-dependent inactivation protocol for evoking transient Ba²⁺ currents consisted of depolarization steps to a test potential of −40 mV (250 ms) from a holding potential ranging from −100 to −40 mV (3.5 s) with 10 mV increments. f Time to peak, TTP, for Ba²⁺ currents recorded in a protocol used to estimate the transient current activation. g Inactivation time constant, τ, obtained from a single-exponential fit of the decaying phase of the currents evoked in the activation protocol. Numbers of cells: 19 cells from 4 rats in control group and 17 cells from 4 rats in diabetic group. Data are expressed as Mean ± S.E.M. *p < 0.02, **p < 0.001