Temporal and spatial properties of cellular Ca2+ flux in trout ventricular myocytes.
Confocal microscopy was used to investigate the temporal and spatial properties of Ca(2+) transients and Ca(2+) sparks in ventricular myocytes of the rainbow trout (Oncorhynchus mykiss). Confocal imaging confirmed the absence of T tubules and the long ( approximately 160 microm), thin ( approximately 8 microm) morphology of trout myocytes. Line scan imaging of Ca(2+) transients evoked by electrical stimulation in cells loaded with fluo 4 revealed spatial inhomogeneities in the temporal properties of Ca(2+) transients across the width of the myocytes. The Ca(2+) wavefront initiated faster, rose faster, and reached larger peak amplitudes in the periphery of the myocyte compared with the center. These differences were exacerbated by stimulation with the L-type Ca(2+) channel agonist (-)BAY K 8644 or by sarcoplasmic reticulum (SR) inhibition with ryanodine and thapsigargin. Results reveal that the shape of the trout myocyte allows for rapid diffusion of Ca(2+) from the cell periphery to the cell center, with SR Ca(2+) release contributing to the cytosolic Ca(2+) rise in a time-dependent manner. Spontaneous Ca(2+) sparks were exceedingly rare in trout myocytes under control conditions (1 sparking cell from 238 cells examined). This is in marked contrast to the rat where a total of 56 spontaneous Ca(2+) sparks were observed in 9 of 11 myocytes examined. Ca(2+) sparklike events were observed in a very small number of trout myocytes (15 sparks from 9 of 378 cells examined) after stimulation with either (-)BAY K 8644 or high Ca(2+) (6 mM). Reducing temperature to 15 degrees C in intact myocytes or permeabilizing myocytes to adjust intracellular conditions to favor Ca(2+) spark detection was without significant effects. Possible reasons for the rarity of Ca(2+) sparks in a cardiac myocyte with an active SR are discussed.
Shiels
Holly A
HA
School of Biomedical Sciences, University of Leeds, UK. holly.shiels@manchester.ac.uk
White
Ed
E
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism; D018613:Microscopy, Confocal; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013997:Time Factors
D002120:Calcium Channel Agonists; D019837:Ryanodine Receptor Calcium Release Channel; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D002118:Calcium