Temperature sensitivity of outward current in cardiac Purkinje fibers
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In cardiac Purkinje fibers the temperature sensitivity of the membrane current flowing after 2 sec in response to depolarizing clamp steps was recorded. When the temperature was quickly lowered (30 sec) from 37°C to 20°C for a period of 2 min the outward current was markedly reduced. The effect was immediately reversed upon rewarming. The reduction in outward current on cooling was most pronounced between 30°C and 20°C.
In the range of anomalous rectification cooling to 20°C shifted the i.v. relation in a negative direction by a constant amount of 20 nA. Outside this potential range (negative to −80 mV and positive to −45 mV) the slope conductance was reduced with a Q10 of about 1.3.
In the presence of dihydroouabain cooling did not further reduce the outward current in the potential range of anomalous rectification. However, negative to −80 mV and positive to −40 mV the slope conductance was reduced.
The results support the view that part of the outward current is generated by an electrogenic sodium pump which is inhibited by cooling.
Key wordsVoltage Clamp Purkinje Fibers Outward Current Temperature Electrogenic Sodium Pump
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