Influences of phenylephrine on delayed afterdepolarization and triggered activity in sheep Purkinje fibers.

AIM

To compare the effects of phenylephrine (Phe) on DAD and TA in the absence or presence of propranolol (Pro).

METHODS

Using intracellular microelectrode methods to record transmembrane potentials in sheep Purkinje fibers.

RESULTS

Perfused Phe 1 mumol.L(-1) for 60 min, in the absence of Pro, Phe increased the amplitude of DAD from 7.5 +/- 1.2 to 9.0 +/- 2.0 mV (n = 8, P < 0.05), nonsignificantly changed the duration of DAD and induced TA in 3/11 preparations; but in the presence of Pro 0.5 mumol.L(-1) blocking beta-adrenoceptors, the amplitude of DAD increased from 7.2 +/- 1.8 to 8.3 +/- 2.1 mV at the first 20 min (n = 8, P < 0.01), and then decreased to 6.3 +/- 1.6 mV, the duration of DAD prolonged from 192 +/- 17 to 280 +/- 27 ms (n = 8, P < 0.01 vs control), meanwhile Phe could suppress the TA induced by acetylstrophanthidin and this effect was blocked by prazosin.

CONCLUSION

When Pro is efficiently used in abolishing arrhythmias evoked by catecholmines, apart from directly blocking beta-adrenoceptors, relatively aggravating excitation of alpha-adrenoceptors to suppress DAD and TA is one of the important reasons.