Figure 1.

Isolation of Na⁺–Ca²⁺ exchanger current (I_Na-Ca) in shark ventricular myocytes. (A) Superimposed membrane currents obtained in external solution containing Ca²⁺- and K⁺-channel inhibitors (10 μM nifedipine, 0.1 mM Ba²⁺, and 5 mM Cs⁺) in response to voltage-clamp protocol shown at the top. (B) Membrane currents obtained under the same experimental conditions but after external 5 mM Ni²⁺. (C) Ni²⁺-sensitive component of the current (I_Na-Ca) obtained after subtraction of current records shown in B from those in A. (D) Original current traces obtained in the absence and presence of 5 mM Ni²⁺ in response to ramp voltage-clamp protocol shown above the original current traces. (E) Current density–voltage relation for Ni²⁺-sensitive I_Na-Ca constructed from ramp-current records shown in D.