Extended Data Figure 4. Shark K_V properties.

a. Voltage-activated currents recorded in HEK293 cells expressing shark (red) or human (black) K_V1.3. Inset: Arrows indicate when currents were measured at −30mV following voltage pulses that increased in 10mV increments from −100mV.

b. (Left) Normalized currents elicited by a 40mV voltage pulse demonstrated that expressed shark K_V channels open more slowly compared with human orthologues. (Right) Average activation kinetics were slower for shark K_V compared with human K_V in response to voltages from 20mV to 50mV. n = 6, p < 0.0001 for contribution of orthologue identity to series variance, two-way ANOVA with post hoc Bonferroni test.

c. Deactivation kinetics of normalized currents from shark and human K_V channels at various repolarizing voltages following an activating prepulse of 40mV. Arrow indicates when current properties were measured during voltage protocol.

d. Inactivation properties (Left) and average inactivation–voltage relationships of shark (red, V_h1/2 = 0.1 ± 2.8mV) and human (black, V_h1/2 = −30.6 ± 0.9mV) K_V1.3 channels. Arrow indicates when inactivation was measured during 40mV pulses following a series of prepulses that increased in 10 mV increments from −100mV. n = 9, p < 0.0001 for V_h1/2, two-tailed Student’s t-test.

e. I_KV was reduced by 4-AP or quinidine in native shark electrosensory cells or heterologously expressed shark K_V1.3. Currents were elicited by increasing voltage pulses from −90mV (native) or −100mV (heterologous).

f. Pharmacological profile of shark electrosensory cell I_KV and heterologously expressed shark K_V1.3. Currents measured at peak amplitude were reduced by 4-AP or quinidine, but not other treatments. Pharmacological modulation of native I_KV and shark K_V1.3 was similar. All data represented as mean ± s.e.m.

g. The short human isoform of K_V1.3 (short N-terminal truncation) was used to study gating currents because of enhanced expression, but channel properties are identical¹⁵. Similarly, we found that activation threshold and G–V relationship, voltage-dependent inactivation, and deactivation were similar between long and short isoforms. n = 6.