sinoatrial tissue of crucian carp heart has only negative contractile responses to autonomic agonists窦房结组织鲫鱼的心只有消极的自主收缩反应受体激动剂.pdfVIP

Vornanen et al. BMC Physiology 2010, 10:10 /1472-6793/10/10 R E S E A R C H A R T I C L E Open Access Research article Sinoatrial tissue of crucian carp heart has only negative contractile responses to autonomic agonists Matti Vornanen*, Mervi Hälinen and Jaakko Haverinen Abstract Background: In the anoxia-tolerant crucian carp (Carassius carassius) cardiac activity varies according to the seasons. To clarify the role of autonomic nervous control in modulation of cardiac activity, responses of atrial contraction and heart rate (HR) to carbacholine (CCh) and isoprenaline (Iso) were determined in fish acclimatized to winter (4°C, cold- acclimated, CA) and summer (18°C, warm-acclimated, WA) temperatures. Results: Inhibitory action of CCh was much stronger on atrial contractility than HR. CCh reduced force of atrial contraction at an order of magnitude lower concentrations (EC50 2.75-3.5·10-8 M) in comparison to its depressive effect on HR (EC -7 50 1.23-2.02·10 M) (P 0.05) without differences between winter and summer acclimatized fish. Inhibition of nitric oxide synthase with 100 μM L-NMMA did not change the response of the sinoatrial tissue to CCh. Reduction of atrial force was associated with a strong shortening of action potential (AP) duration to ~50% (48 ± 10 and 50 ± 6% for CA and WA fish, respectively) and 11% (11 ± 3 and 11 ± 2% for CA and WA fish, respectively) of the control value at 3·10- 8 M and 10-7 M CCh, respectively (P 0.05). In atrial myocytes, CCh induced an inwardly rectifying K+ current, IK,CCh, with an EC50 value of 3-4.5·10-7 M and inhibited Ca2+ current (ICa) by 28 ± 8% and 51 ± 6% at 10-7 M and 10-6 M, respectively. These currents can explain the shortening of AP. Iso did not elicit any responses in crucian carp sinoatrial preparations nor did it have any effec