Figure 2.

The effects of isoproterenol (ISO), forskolin (FSK), and KB-R7943 on I_Na-Ca in shark ventricular myocytes. (A) Ramp voltage-clamp protocol and corresponding original currents obtained in control external solution (trace 1), after application of 5 mM Ni²⁺ (trace 2), after addition of 5 μM ISO (trace 3), and after treatment of 5 mM Ni²⁺ in the presence of ISO (trace 4). (B) Time course of changes of the steady-state outward current density at +60 mV in response to voltage-clamp pulses shown in A. (C) Ramp voltage-clamp protocol and corresponding currents obtained in control (trace 1), after 5 mM Ni²⁺ (trace 2), after addition of 10 μM FSK (trace 3), and after treatment with 5 mM Ni²⁺ in FSK (trace 4). (D) Time course of changes of the steady-state outward current density at +60 mV shown in C. The effect of KB-R7943 on I_Na-Ca in shark ventricular myocytes. (E) Ramp voltage-clamp protocol and corresponding currents obtained in control (trace 1), in 5 mM Ni²⁺ (trace 2), after addition of 10 μM KB-R7943 (trace 3), and after 5 mM Ni²⁺ in KB-R7943 (trace 4). (F) Time course of changes of the steady-state outward current density at +60 mV shown in E. Pulses were delivered at a frequency of 0.1 Hz. Numbers along the experimental points in B, D, and F mark traces shown in A, C, and E, respectively. I_out was measured at 50 ms after the onset of depolarization to +60 mV and normalized to the cell capacitance to yield current density (pA/pF).