The effects of dopamine on the transmembrane action potentials of electrically driven left auricle and right papillary muscle of guinea pig were studied in Tyrode solution and in 25 mM K+-Tyrode solution. Under physiological conditions dopamine at concentration <10-6M had no effect, at concentrations between 10-6 and 10-4M it slightly increased the resting potential (RP), caused a marked increase of the overshoot (OS), but did not change the maximum rate of rise (V(max)) of the action potential (AP). The duration of AP was significantly enhanced by 10-6 and 10-5M but was shortened by 10-4M dopamine. The effects of dopamine on AP were antagonized by pindolol (4 x 10-7M) but not by phentolamine (5 x 10-6M). In the atrium in which the fast sodium channels were blocked by partial depolarization (25 mM K+-Tyrode) and the preparation was inexcitable, dopamine in high concentrations (10-4-2.5 x 10-4M) restored the electrical and mechanical activity. Dopamine induced APs having very slow rate of rise and low RP, characteristics of the given extracellular K+ concentration. The slow electrical responses were unaffected by haloperidol (10-5M), but were abolished by pindolol. The effects of dopamine and adrenaline on the depressed fast Na+ system (using 4 mM to 20 mM K+-Tyrode solution) were compared in the papillary muscle. The steady state inactivation of V(max) was shifted by 6 mV to more negative potentials by adrenaline (5 x 10-6M) and by 3 mV to more negative potentials by dopamine (2.5 x 10-4M). Our results suggest that in the guinea-pig auricular preparation dopamine acts similarly to adrenaline and isoprenaline through the activation of beta-adrenergic receptor. However, dopamine influences the inactivation process of the fast Na+ channel much weaker than adrenaline.
|Number of pages||9|
|Journal||Polish journal of pharmacology and pharmacy|
|Publication status||Published - Dec 1 1985|
ASJC Scopus subject areas
- Pharmaceutical Science