Membrane and calcium clock mechanisms contribute variably as a function of temperature to setting cardiac pacemaker rate in zebrafish Danio rerio

• Published in: Journal of fish biology Vol. 95; no. 5; pp. 1265 - 1274
• Main Authors: Marchant, James L., Farrell, Anthony P.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.11.2019; Wiley Subscription Services, Inc
• Subjects: Acclimation; Acclimatization; Acclimatization - physiology; Animals; Calcium; Calcium - metabolism; Calcium Signaling; Channels; Danio rerio; EKG; Electrocardiography; fish; Freshwater fishes; HCN channels; Heart - physiology; heart failure; Heart Rate; Ion channels (cyclic nucleotide-gated); Membranes; Nucleotides; pacemaker; Ryanodine; Temperature; temperature acclimation; Thapsigargin; Zebrafish; Zebrafish - anatomy & histology; Zebrafish - physiology; heart rate; temperature acclimation; pacemaker; zebrafish; HCN channels; Danio rerio
• ISSN: 0022-1112; 1095-8649; 1095-8649
• DOI: 10.1111/jfb.14126

Here, we show that heart rate in zebrafish Danio rerio is dependent upon two pacemaking mechanisms and it possesses a limited ability to reset the cardiac pacemaker with temperature acclimation. Electrocardiogram recordings, taken from individual, anaesthetised zebrafish that had been acclimated to 18, 23 or 28°C were used to follow the response of maximum heart rate (fHmax) to acute warming from 18°C until signs of cardiac failure appeared (up to c. 40°C). Because fHmax was similar across the acclimation groups at almost all equivalent test temperatures, warm acclimation was limited to one significant effect, the 23°C acclimated zebrafish had a significantly higher (21%) peak fHmax and reached a higher (3°C) test temperature than the 18°C acclimated zebrafish. Using zatebradine to block the membrane hyperpolarisation‐activated cyclic nucleotide–gated channels (HCN) and examine the contribution of the membrane clock mechanisms to cardiac pacemaking, f Hmax was significantly reduced (by at least 40%) at all acute test temperatures and significantly more so at most test temperatures for zebrafish acclimated to 28°C vs. 23°C. Thus, HCN channels and the membrane clock were not only important, but could be modified by thermal acclimation. Using a combination of ryanodine (to block sarcoplasmic calcium release) and thapsigargin (to block sarcoplasmic calcium reuptake) to examine the contribution of sarcoplasmic reticular handling of calcium and the calcium clock, f Hmax was again consistently reduced independent of the test temperature and acclimation temperature, but to a significantly lesser degree than zatebradine for zebrafish acclimated to both 28 and 18°C. Thus, the calcium clock mechanism plays an additional role in setting pacemaker activity that was independent of temperature. In conclusion, the zebrafish cardiac pacemaker has a limited temperature acclimation ability compared with known effects for other fishes and involves two pacemaking mechanisms, one of which was independent of temperature.