May 14, 2007  Enzyme Points Way to Pacemaker Drug

A heart beats three billion times in an average life span – and sometimes those beats race, like when we run into a Grizzly bear or climb stairs or fall in love. Such moments can more than double the average heart rate of 70 beats per minute, speeding it up to 160 beats. And we feel it. Palpitations, dizziness, breathlessness.

Scientists have a good idea what causes a racing heart: an increase in adrenaline sends a signal to the pacemaker cell, located in the upper right chamber. This cell then sets off a domino effect that speeds up the muscle contractions. What scientists don't understand, though, is what makes the heart beat slow back down.  But a team at the University of Illinois at Chicago says they've found a promising clue. They've isolated an enzyme called "P-21 activated kinase," or Pak 1, that affects the electrical channels inside the pacemaker cell.  The scientists have shown that by turning on Pak 1 they can reduce electrical channel activity and slow down the heart.  They're now working on finding a drug treatment that can control this enzyme, hoping that a medicine might replace artificial pacemakers.  Be still my beating heart.