Abstract
To determine whether Na/Ca exchange is altered in primary hypertension, Na-dependent changes in intracellular Ca, ([Ca](i)), were measured in isolated perfused hearts from Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats. Intracellular Na, (Na(i), mEq/kg dry wt), and [Ca](i) were measured by NMR spectroscopy. Control [Ca](i) was less in WKY than SHR (176 ± 18 vs 253 ± 21 nmol/l; mean ± S.E., P < 0.05), whereas Na(i) was not significantly different. One explanation for this is that net Na/Ca exchange flux is decreased in SHR. If this hypothesis is correct, the rate of Ca uptake in SHR should be less than WKY when Na/Ca exchange is reversed by decreasing the transmembrane Na gradient. The Na gradient was reduced by decreasing extracellular Na, ([Na](o)) and/or by increasing [Na](i). To increase [Na](i), Na uptake was stimulated by acidification while Na extrusion by Na/K ATPase was inhibited by K-free perfusion. Seventeen minutes after acidification, Na(i) had increased but was not significantly different in SHR and WKY (18.0 ± 2.3 to 57.4 ± 7.6 vs 20.3 ± 0.6 to 66.5 ± 4.8 mEq/kg dry wt, respectively). Yet [Ca](i) was greater in WKY than SHR (1768 ± 142 vs 1201 ±90 nmol/l; P < 0.05). [Ca](i) was also measured after decreasing [Na](o) from 141 to 30 mmol/l. Fifteen minutes after reducing [Na](o), [Ca](i) was greater in WKY than SHR (833 ± 119 vs 425 ± 94 nmol/l; P < 0.05). Thus for both protocols, decreasing the transmembrane Na gradient led to increased [Ca](i) in both SHR and WKY, but less increase in SHR. The results are consistent with the hypothesis that Na/Ca exchange activity is less in SHR than WKY myocardium.
Original language | English (US) |
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Pages (from-to) | 299-309 |
Number of pages | 11 |
Journal | Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology |
Volume | 123 |
Issue number | 3 |
DOIs | |
State | Published - Jul 1999 |
Keywords
- Intracellular calcium
- Intracellular sodium
- Na/Ca exchange
- Spontaneously hypertensive rat heart
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Physiology