Differences in ionic currents between canine myocardial and Purkinje cells. Issue 3 (22nd August 2013)

• Record Type: Journal Article
• Authors: Vassalle, Mario; Bocchi, Leonardo
• Is Part Of: Physiological reports. Volume 1:Issue 3(2013:Aug.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2013-08-22
• Subjects: Physiology -- Periodicals; 571
• DOI: 10.1002/phy2.36
• Languages: English
• ISSNs: 2051-817X

Abstract

<abstract abstract-type="main" id="phy236-abs-0001"> <title>Abstract</title> <p>An electrophysiological analysis of canine single ventricular myocardial (VM) and Purkinje (P) cells was carried out by means of whole cell voltage clamp method. The following results in VM versus P cells were obtained. I<sub>N</sub><sub>a3</sub> was present, had a threshold negative to the fast activating–inactivating I<sub>N</sub><sub>a1</sub>, its slow inactivation was cut off by I<sub>N</sub><sub>a1</sub>, and contributed to Na<sup>+</sup> influx at I<sub>N</sub><sub>a1</sub> threshold. I<sub>N</sub><sub>a1</sub> was smaller and had a less negative threshold. There was no comparable slowly inactivating I<sub>N</sub><sub>a2</sub>, accounting for the shorter action potential. Slope conductance at resting potential was about double and decreased to a minimum value at the larger and less negative I<sub>K</sub><sub>1</sub> peak. The negative slope region of I‐V relation was smaller during fast ramps and larger during slow ramps than in P cells, occurred in the voltage range of I<sub>K</sub><sub>1</sub> block by Mg<sup>2+</sup>, was not affected by a lower V<sub>h</sub> and TTX and was eliminated by Ba<sup>2+</sup>, in contrast to P cells. I<sub>C</sub><sub>a</sub> was larger, peaked at positive potentials and was eliminated by Ni<sup>2+</sup>. I<sub>to</sub> was much smaller, began at more positive values, was abolished by less negative V<sub>h</sub> and by 4‐aminopyridine, included a sustained current that 4‐aminopyridine decreased but did not eliminate. Steeper ramps increased I<sub>K</sub><sub>1</sub> peak as well as the fall in outward current during repolarization, consistent with a time‐dependent block and unblock of I<sub>K</sub><sub>1</sub> by polyamines. During repolarization, the positive slope region was consistently present and was similar in amplitude to I<sub>K</sub><sub>1</sub> peak, whereas it was small or altogether missing in P cells. The total outward current at positive potentials comprised a larger I<sub>K</sub><sub>1</sub> component whereas it included a larger I<sub>to</sub> and sustained current in P cells. These and other results provide a better understanding of the mechanisms underlying the action potential of VM and P cells under normal and some abnormal (arrhythmias) conditions.</p> </abstract>