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

Abstract

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.

Drivers of Sinoatrial Node Automaticity in Zebrafish: Comparison With Mechanisms of Mammalian Pacemaker Function

“…Past studies also support the importance of RyR and intracellular Ca 2+ cycling for zebrafish SAN automaticity shown in our study, as ryanodine (intraperitoneal injection of 50 ng/g), combined with thapsigargin (1.3 µg/g, to block SR Ca 2+ reuptake) reduced HR by ∼40% (Marchant and Farrell, 2019). A similar result has been shown in another teleost (the trout), in which ryanodine (10 µM) and thapsigargin (1 µM) resulted in a 44% decrease in HR (Haverinen and Vornanen, 2007).…”

“…The first indication of the currents involved in zebrafish SAN automaticity came from the discovery of a mutation (slow mo) that caused a reduction in HR by affecting a hyperpolarisation-activated inward current with similar properties to I f (Baker et al, 1997;Warren et al, 2001). More recently, the general involvement of the membrane and Ca 2+ "clocks" in SAN automaticity were investigated using pharmacological interventions, which confirmed the role of I f (block of HCN channels reduced HR by ∼65%) and demonstrated a role for intracellular Ca 2+ cycling (block of SR Ca 2+ release with ryanodine, combined with block of SR Ca 2+ reuptake with thapsigargin reduced HR by ∼40%) (Marchant and Farrell, 2019). Yet, the potential involvement of other membrane and Ca 2+ "clock" mechanisms (i.e., I Ca , T , I Ca , L ) and the relative importance of these two pacemaker systems for SAN automaticity in the zebrafish has not been explored.…”

Atlantic Salmon (Salmo salar) Cage-Site Distribution, Behavior, and Physiology During a Newfoundland Heat Wave

“…At present, the mechanism(s) mediating this effect in fish is/are not completely understood. However, Marchant and Farrell ( 2019 ) recently showed that the pacemaker cells of the heart have both membrane and calcium “clocks,” and suggest that the latter is involved in the control of heart rate with changes in temperature.…”

A rapid intrinsic heart rate resetting response with thermal acclimation in rainbow trout, Oncorhynchus mykiss

“…Our study is the first in fishes to examine the mRNA expression of components of the calcium and the membrane clock in SAN tissue. Both clocks are hypothesised to drive spontaneous depolarisation of pacemaker cells in the SAN in mammals, and evidence exists that this may (Hassinen et al, 2017;Marchant and Farrell, 2019), or may not be the case in fishes (Wilson and Farrell, 2013). Therefore, the differentially higher expression of HCN1, a membrane clock component, observed in the SAN compared with the atrial tissues is of significant interest.…”