Fig. 3. Na⁺-Ca²⁺ exchange current (I_NCX) measured as the Ni²⁺-sensitive current during the hyperpolarising phase of the ramp pulse in ventricular myocytes from the burbot heart. (A) Values are means ± s.e.m. from 8 cells at 4°C and 11°C when the intracellular solution contained 20 mmol l^-1 BAPTA. ^*Density of I_NCX is increased significantly by acute warming to 11°C (Student's t-test, P<0.005). (B) Mean values (± s.e.m.) from 9 cells at 4°C only. The pipette solution contained a lower level of Ca²⁺ buffering (0.025 mmol l^-1 EGTA). Insets show voltage ramp protocols.