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Ionic currents during sustained pacemaker activity in rabbit sino‐atrial myocytes
Author(s) -
Zaza Antonio,
Micheletti Maria,
Brioschi Angelica,
Rocchetti Marcella
Publication year - 1997
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1997.677ba.x
Subject(s) - diastolic depolarization , chemistry , depolarization , myocyte , biophysics , medicine , conductance , patch clamp , channel blocker , diastole , hyperpolarization (physics) , voltage clamp , electrophysiology , current (fluid) , endocrinology , membrane potential , calcium , sinoatrial node , stereochemistry , biology , biochemistry , physics , heart rate , organic chemistry , blood pressure , condensed matter physics , thermodynamics , nuclear magnetic resonance spectroscopy
1 The contribution of various ionic currents to diastolic depolarization (DD) in rabbit sino‐atrial myocytes was evaluated by the action potential clamp technique. Individual currents were identified, during sustained pacemaking activity reproduced under voltage clamp conditions, according to their sensitivity to supecific channel blockers. 2 The current sensitive to dihydropyridines (DHPs), blockers of L‐type Ca 2+ current ( I Ca,L ), was small and outward during most of DD. Diastolic DHP‐sensitive current was affected by changes in the driving force for K + , but it was insensitive to E‐4031, which blocks the current termed I K,r ; it was abolished by cell dialysis with a Ca 2+ chelator. 3 The current sensitive to 2 m m Cs + ( I Cs ), a blocker of hyperpolarization‐activated current ( I f ), was inward during the whole DD and it was substantially larger than the net inward current flowing during this phase. However, diastolic I K,r , identified in the same cells as the current sensitive to the blocker E‐4031, exceeded I Cs 2‐fold. 4 These findings suggest that: (a) Ca 2+ influx during the pacemaker cycle increases a K + conductance, thus inverting the direction of the net current generated by L‐type Ca 2+ channel activity during DD; (b) the magnitude of I f would be adequate to account fully for DD; however, the coexistence of a larger I K,r suggests that other channels besides I f contribute inward current during this phase.