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- Title
Altered sodium-calcium exchange in afferent arterioles of the spontaneously hypertensive rat.
- Authors
Nelson, Lawrence D.; Mashburn, Nicole A.; Bell, P. Darwin
- Abstract
Studies were performed to determine if there is a derangement in Na-Ca exchange activity in afferent (AA) and efferent (EA) arterioles from 3- and 9-week-old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Cytosolic calcium concentration ([Ca2+]i) was assessed using microscope-based photometry in fura-2 loaded arterioles bathed in a Ringer's solution. Baseline [Ca2+]i was similar in the AA of 3- and 9-week-old WKY and SHR. In AA from 3-week-old rats, [Ca2+]i increased by 89 ± 15 nM in WKY and by 73 ± 13 nM in SHR during decreases in bath sodium concentration ([Na+]e) from 150 to 2 mM (Na+ replaced with n-methyl-D-glutamine). In 9-week-old hypertensive SHR (SBP = 150 mm Hg), increases in [Ca2+]i were attenuated (24 ± 3 nM) relative to 3-week-old WKY and SHR, and 9-week-old WKY (90 ± 9 nM; <em>p</em> < 0.05). Likewise, the rate of removal of Ca2+ in the continued presence of 2 mM Nae (Ca2+ sequestration and/or extrusion) was markedly reduced in AA of 9-week-old SHR (-0.15 ± 0.03 nM/second) versus 3-week-old SHR (-0.72 ± 0.12 nM/second) and 3- and 9-week-old WKY (-0.49 ± 0.10 and -0.67 ± 0.14 nM/second). In other experiments, AAs were preincubated in 1 mM ouabain to increase intracellular [Na+]. This maneuver augmented the increase in [Ca2+]i obtained with removal of Na+e; however, the responses obtained in 9-week-old SHR arterioles were still attenuated compared to those obtained in arterioles for 3- and 9-week-old WKY and 3-week-old SHR. These results suggest that exchanger number and/or sensitivity to the transmembrane Na gradient was reduced in the SHR AA. In EA, baseline [Ca2+]i was similar in 3- and 9-week-old WKY and SHR. In contrast to AA, the magnitude of Na-dependent and Na-independent changes in [Ca2+]i was not different in the EA of 3- and 9-week-old WKY and SHR. These results indicate that regulation of Na-Ca exchange activity may differ between AA and EA segments. Furthermore, diminished Na-Ca exchange and Na-independent Ca2+ sequestering/extrusion mechanisms could contribute to altered AA [Ca2+]i in the SHR.
- Subjects
PHOTOMETRY; ELECTROMAGNETIC measurements; RADIATION measurements; ARTERIES; BLOOD vessels; AMINO acids
- Publication
Kidney International, 1996, Vol 50, Issue 6, p1889
- ISSN
0085-2538
- Publication type
Article
- DOI
10.1038/ki.1996.510