Tyrosine kinase receptors (VEGFR and EGFR) regulate normal automaticity of heart pacemaker, the sinoatrial node.

National Institute On Aging

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Abstract

(1) We discovered that EGFR and VEGFR1/2 including their downstream targets PLC and PKC (assessed by RT-qPCR) are expressed in the SA node with expression levels comparable to those in ventricle. (2) Selective EGFR inhibitors AG1478 and PD153035 markedly decreased the spontaneous SANC beating rate (perforated patch-clamp technique) and this effect was largely reversible upon drug washout, indicating that EGFR is active in the basal state. Effects of both EGFR inhibitors were further tested on parameters of the “Coupled clock” pacemaker system. Both AG1478 and PD153035 markedly decreased the LCR size and number per each spontaneous cycle (confocal microscopy, Ca2+ indicator Fluo-3AM) and prolonged the LCR period (the interval between AP-induced Ca2+ transient and subsequent LCR), accompanied by the concomitant increase in the spontaneous cycle length. We also investigated effects of Vatalanib (VEGFR1/2/3 inhibitor) on the “Coupled clock” pacemaker system. Vatalanib markedly suppressed LCR parameters, i.e., decreased the LCR size and number per each spontaneous cycle and prolonged the LCR period accompanied by increase in the spontaneous cycle length. Overall, vatalanib reduced the spontaneous SANC beating rate by ~50% and produced arrhythmic behavior of isolated SANC. The selective VEGFR2 inhibitor ZM-323881, however, suppressed spontaneous firing only in few SANC indicating that VEGFR1, but not VEGFR2, is likely the key modulator of basal cardiac automaticity. (3) Since both phosphoinositide-3-kinase (PI3-K) and phospholipase C (PLC) are downstream targets of EGFR and VEGFR we studied how inhibition of these targets would affect LCR parameters and spontaneous SANC firing. While selective PI3-K inhibitor PI-103 was lacking effects, PLC inhibitor U-73122, but not its inactive analog U-73343, markedly decreased the LCR size, number, extended the LCR period and prolonged the spontaneous SANC cycle length. Inhibition of basal PLC or PKC activation also markedly suppressed spontaneous firing of SANC. Therefore, activities of both EGFR and VEGFR regulate normal spontaneous firing of SANC via modulation of the “Coupled clock” pacemaker system. Specifically, EGFR and VEGFR activation increases the LCR size and number of LCR per each spontaneous cycle and shortens the LCR period which predicts activation of inward Na+-Ca2+ exchange current and, therefore, the spontaneous SANC firing in the basal state. Our results strongly suggest that cancer treatments employing EGFR or VEGFR inhibitors will likely have harmful effects on spontaneous firing of cardiac pacemaker cells, ultimately leading to the SA node dysfunction. (4) Although adverse effects of Erlotinib, including myocardial infarction/ischemia as well as fatal events, have been reported, the mechanism of these adverse effects remains unknown. We discovered that, similar to AG1478 or PD153035, Erlotinib decreased spontaneous beating of SANC via suppression of the Coupled-clock pacemaker system. Specifically, Erlotinib significantly decreased LCR size and number per each spontaneous cycle and extended the LCR period, leading to prolongation of the spontaneous SANC cycle length. Overall, Erlotinib (10-30 mkmol/L) decreased spontaneous SANC firing by ~25%. The suppression of cardiac pacemaker function might contribute to the adverse effects of Erlotinib observed in patients.