Fig. 1
Functional properties of the Cav3.2 R132H variant associated with epilepsy and hearing loss. a AlphaFold model of the human Cav3.2 channel showing the location of the R132H mutation (left panel). In this model, the arginine (R) 132 is located within the extracellular-exposed proximal end of the second transmembrane helix (S2) of Cav3.2 and forms two intra-helix hydrogen bonds with serine (S) 130 and leucine (L) 136 (left panel). Substitution of the R132 with a histidine (H) residue creates an additional hydrogen bond with methionine (M) 119 located within the first transmembrane helix (S1) of the channel. b Representative sets of whole-cell T-type current traces recorded in tsA-201 cells expressing Cav3.2 wild-type (WT) (black traces) and R132H variant (red traces). Currents were elicited by depolarizing steps to values ranging between − 90 mV and + 30 mV from a holding potential of − 100 mV. c Corresponding mean current/voltage (I/V) relationships. The continuous lines represent the fit of the I/V curves with the modified Boltzmann Eq. (1). d Corresponding mean maximal macroscopic conductance values (Gmax) obtained from the fit of the I/V curves. e Corresponding mean normalized voltage dependence of activation fitted (continuous lines) with the modified Boltzmann Eq. (2). The inset shows the mean half-activation potential values obtained from the fit of the conductance curves. f Mean normalized voltage dependence of steady-state inactivation fitted with the two-state Boltzmann Eq. (3). The inset represents the mean half-inactivation potential values obtained from the fit of the inactivation curves. g Mean normalized recovery from inactivation kinetic fitted with the single-exponential function (4). Inset shows the mean time constant values obtained from the fit of the recovery from inactivation curves. h Mean time constant of fast activation (diamond symbols) and inactivation (round symbols) kinetics of T-type currents as a function of the membrane potential. i Relative change in peak current amplitude in response to extracellular pH alkalinization (pHe 8.0, green symbols) and acidification (pHe 6.5, orange symbols) from physiological pHe 7.2 (top panels) as well as corresponding mean current change amplitude values (bottom panels). T-type currents were elicited by repetitive depolarizing steps to -20 mV from a holding potential of -100 mV. j, k Legend same as (i) but for T-type current activation and inactivation kinetics. Data are presented as mean ± S.E.M. and statistical analysis was performed using a two-tailed Student’s t test