Measurement of Funny Current (If) Channel in Human Atrial Tissue: Correlation with Left Atrial Filling Pressure and Atrial Fibrillation.

Introduction: The funny current (I-f)contributes to phase IV spontaneous depolarization in cardiac pacemaker tissue. Enhanced I-f activity in myocardial tissue may lead to increased automaticity and therefore tachyarrhythmia. We measured the amount of I-f activity in the messenger ribonucleic acid (mRNA) in human atrial tissue and correlated the mRNA amount to left atrial filling pressure and atrial fibrillation (AF). Methods and Results: A total of 34 patients undergoing open heart surgery were included ( 15 men and 19 women, aged 55 +/- 10 years). Atrial tissue was obtained from the right atrial free wall, the right atrial appendage, the left atrial free wall, and the left atrial appendage, respectively. The mRNA amount of the I-f channel was measured by reverse transcription polymerase chain reaction and was normalized to the mRNA levels of glyceraldehyde 3-phosphate dehydrogenase. We found that the I-f channel mRNA was present at all the atrial sampling sites. A higher left atrial filling pressure, an indicator of congestive heart failure, was associated with a higher I- f mRNA level (r(2) = 0.446, P < 0.01 by linear regression). We also found that the mRNA amount was significantly higher in patients with AF than in patients without AF (1.68 +/- 0 . 49 vs 1.27 + /- 0.43; P < 0.05). Age, sex, right atrial filling pressure, left atrial dimension, and left ventricular ejection fraction had no significant effect on the mRNA level. Conclusion: The mRNA of the I-f channel is present in the free-wall area and appendage area from both atria. Increased left atrial filling pressure and clinical AF are associated with increased I-f mRNA level.