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The Journal of Experimental Biology 205, 3641-3650 (2002)
Copyright © 2002 The Company of Biologists Limited

Effects of temperature on intracellular [Ca²⁺] in trout atrial myocytes

Holly A. Shiels^1,*, Matti Vornanen² and Anthony P. Farrell¹

¹ Simon Fraser University, Biological Sciences, Burnaby, British Columbia, V5A 1S6, Canada
² University of Joensuu, Department of Biology, PO Box 111, 80101 Joensuu, Finland

^* Author for correspondence at present address: School of Biomedical Sciences, University of Leeds, Leeds, LS2 9JT, UK (e-mail: hollys{at}sfu.ca)

Accepted 21 August 2002

Acute temperature change can be cardioplegic to mammals, yet certain ectotherms maintain their cardiac scope over a wide temperature range. To better understand the acute effects of temperature on the ectothermic heart, we investigated the stimulus-induced change in intracellular Ca²⁺ concentration ([Ca²⁺]_i; cytosolic Ca²⁺ transient) in isolated rainbow trout myocytes at 7°C, 14°C and 21°C. Myocytes were voltage-clamped and loaded with Fura-2 to measure the L-type Ca²⁺ channel current (I_Ca) and [Ca²⁺]_i during physiological action potential (AP) pulses at frequencies that correspond to trout heart rates in vivo at 7°C, 14°C and 21°C. Additionally, [Ca²⁺]_i and I_Ca were examined with square (SQ) pulses at slow (0.2 Hz) and physiologically relevant contraction frequencies. The amplitude of [Ca²⁺]_i decreased with increasing temperature for both SQ and AP pulses, which may contribute to the well-known negative inotropic effect of warm temperature on contractile strength in trout hearts. With SQ pulses, [Ca²⁺]_i decreased from 474±53 nmol l^-1 at 7°C to 198±21 nmol l^-1 at 21°C, while the decrease in [Ca²⁺]_i with AP pulses was from 234±49 nmol l^-1 to 79±12 nmol l^-1, respectively. Sarcolemmal Ca²⁺ influx was increased slightly at cold temperatures with AP pulses (charge transfer was 0.27±0.04 pC pF^-1, 0.19±0.03 pC pF^-1 and 0.13±0.03 pC pF^-1 at 7°C, 14°C and 21°C, respectively). At all temperatures, cells were better able to maintain diastolic Ca²⁺ levels at physiological frequencies with AP pulses compared with 500 ms SQ pulses. We suggest that temperature-dependent modulation of the AP is important for cellular Ca²⁺ regulation during temperature and frequency change in rainbow trout heart.

Key words: L-type Ca²⁺ current (I_Ca), calcium transient, sarcoplasmic reticulum, action potential, frequency, fish hearts, temperature, rainbow trout, Oncorhynchus mykiss

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