Effects of temperature on intracellular Ca2+ in trout atrial myocytes.
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 Ca(2+) concentration ([Ca(2+)](i); cytosolic Ca(2+) transient) in isolated rainbow trout myocytes at 7 degrees C, 14 degrees C and 21 degrees C. Myocytes were voltage-clamped and loaded with Fura-2 to measure the L-type Ca(2+) channel current (I(Ca)) and [Ca(2+)](i) during physiological action potential (AP) pulses at frequencies that correspond to trout heart rates in vivo at 7 degrees C, 14 degrees C and 21 degrees C. Additionally, [Ca(2+)](i) and I(Ca) were examined with square (SQ) pulses at slow (0.2 Hz) and physiologically relevant contraction frequencies. The amplitude of [Ca(2+)](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, [Ca(2+)](i) decreased from 474+/-53 nmol l(-1) at 7 degrees C to 198+/-21 nmol l(-1) at 21 degrees C, while the decrease in [Ca(2+)](i) with AP pulses was from 234+/-49 nmol l(-1) to 79+/-12 nmol l(-1), respectively. Sarcolemmal Ca(2+) 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 degrees C, 14 degrees C and 21 degrees C, respectively). At all temperatures, cells were better able to maintain diastolic Ca(2+) 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 Ca(2+) regulation during temperature and frequency change in rainbow trout heart.
Shiels
Holly A
HA
Simon Fraser University, Biological Sciences, Burnaby, British Columbia, V5A 1S6, Canada. hollys@sfu.ca
Vornanen
Matti
M
Farrell
Anthony P
AP
D000200:Action Potentials; D000818:Animals; D002118:Calcium / Q000032:analysis*; D004553:Electric Conductivity; D004558:Electric Stimulation; D005456:Fluorescent Dyes; D016257:Fura-2; D006325:Heart Atria / Q000737:chemistry / Q000166:cytology; D006339:Heart Rate; D009200:Myocardial Contraction; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012996:Solutions; D013696:Temperature
D005456:Fluorescent Dyes; D012996:Solutions; D002118:Calcium; D016257:Fura-2