Abstract
This study investigated the modulatory effect of magnesium (Mg++) on basal and agonist-stimulated intracellular free calcium (Ca++) concentration ([Ca++]i) in vascular smooth muscle cells from spontaneously hypertensive rats (SHR). Effects of increasing extracellular Mg++ concentration ([Mg++]e) on vasopressin (AVP)-induced [Ca++]i responses were determined in primary cultured unpassaged vascular smooth muscle cells from mesenteric and aortic vessels (representing resistance and conduit arteries, respectively) of Wistar Kyoto rats (WKY) and SHR. [Ca++]i was measured by fura-2 methodology. Underlying mechanisms for Mg++ actions were determined in Ca++-free buffer and in the presence of diltiazem (10−6 M), an l-type Ca++ channel blocker. Basal and AVP-stimulated [Ca++]iresponses were significantly increased (p < .05) in SHR (pD2 = 8.3 ± 0.1, Emax = 532 ± 14 nM for SHR; pD2 = 8.0 ± 0.04,Emax = 480 ± 15 nM for WKY). [Mg++]e dose-dependently reduced basal and agonist-induced [Ca++]i responses. High [Mg++]e (4.8 mM) attenuated [Ca++]i responses to AVP in WKY (Emax = 328 ± 30 nM) and SHR (Emax = 265 ± 27 nM) and normalized AVP-elicited hyper-responsiveness in SHR (pD2 in high [Mg++]e, 8.1 ± 0.3 for SHR, 7.8 ± 0.6 for WKY). Extracellular Ca++ withdrawal and diltiazem abolished the attenuating effects of high [Mg++]e in WKY but not in SHR. These findings demonstrate that Mg++ dose-dependently reduces [Ca++]i and that high [Mg++]e attenuates AVP-stimulated [Ca++]i responses and normalizes sensitivity to AVP in SHR. In WKY, Mg++ actions are dependent primarily on Ca++ influx through l-type Ca++channels, whereas in SHR, the modulatory effects of [Mg++]e are mediated both by Ca++influx through Ca++ channels and by intracellular Ca++ release.
Footnotes
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Send reprint requests to: Rhian M. Touyz, M.D., Ph.D., Clinical Research Institute of Montreal, 110 Pine Avenue West, Montreal (Quebec) Canada, H2W 1R7.
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↵1 This work was supported by a grant from the Heart and Stroke Foundation of Quebec.
- Abbreviations:
- Ca++
- calcium
- Mg++
- magnesium
- Ca++i
- intracellular free calcium concentration
- Mg++e
- extracellular magnesium concentration
- AVP
- vasopressin
- WKY
- Wistar Kyoto rats
- SHR
- spontaneously hypertensive rats
- DOCA
- deoxycorticosterone acetate
- DMEM
- Dulbecco’s modified Eagle’s medium
- VSMC
- vascular smooth muscle cells
- IRCM
- Clinical Research Institute of Montreal
- Received May 19, 1997.
- Accepted November 10, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
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