Aims: 

Phosphatidylinositol-(4,5)bisphosphate (PIP₂) levels in the plasma membrane regulates many channels and transporters relevant to cardiac tissue. Whether PIP₂ regulates gap junctional intercellular coupling (GJIC) in cardiomyocytes is unknown, but could add to the risk of arrhythmia during stimulation of Gaq-coupled receptors Hypothesis: PIP2 regulates GJIC and stimulation with Gaq-coupled agonists reduces GJIC partly due to a reduction of PIP2.

Methods: 

GJIC was measured by dye transfer after localized electroporation of Lucifer Yellow in cultured cardiomyocytes from neonatal rats. Conduction velocity (CV) was measured in cardiomyocytes grown on electrode arrays.

Results: 

One hour wortmannin exposure reduced GJIC indicating that PIP2-depletion inhibits GJIC. In contrast, hypertonic shock, which increases PIP2, increased GJIC. GJIC was inhibited by AngII and noradrenaline stimulation. To test if the reduction in GJIC after agonist stimulation was caused by PIP2-depletion; myocytes were stimulated by AngII and then allowed to recover in control medium with or without wortmannin. GJIC fully recovered in control medium whereas no recovery occurred in the presence of wortmannin. Inhibition of PKC did not affect the response to either AngII or noradrenaline. Also inhibition of arachidonic acid production did not affect the response to agonist stimulation. In beating myocytes CV was reduced by AngII stimulation. After wash-out, CV recovered and this recovery was prevented by inhibition of PIP2 production.

Conclusion: 

Reductions in PIP2 inhibits GJIC in cardiomyocytes, and stimulation by physiologically relevant agonists can reduce PIP2 and thereby GJIC by this mechanism. This reduction lowered CV, which could lead to increased susceptibility to arrhythmias.