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1 Department of Cell & Molecular Physiology and Program in Integrative Vascular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
* To whom correspondence should be addressed. E-mail: arends{at}med.unc.edu.
Although L-type voltage-dependent calcium channels play a major role in mediating vascular smooth muscle cell contraction in the renal vasculature, non-L-type calcium entry mechanisms represent a significant component of vasoactive agonist-induced calcium entry in these cells as well. To investigate the role of these non-voltage-dependent calcium entry pathways in the regulation of renal microvascular reactivity, we have characterized the function of store- and receptor-operated channels (SOCs and ROCs) in renal cortical interlobular arteries (ILAs) of rats. Using fura-2-loaded, microdissected ILAs, we find that the L-type channel antagonist nifedipine blocks less than half the rise in intracellular calcium concentration ([Ca2+]i) elicited by norepinephrine. SOCs were activated in these vessels using the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) inhibitors cyclopiazonic acid and thapsigargin, and were dosedependently blocked by the SOC antagonists Gd3+ and 2-aminoethoxydiphenyl borate (2-APB) and the combined SOC/ROC antagonist SKF96365. Gd3+ had no effect on the non-L-type Ca2+ entry activated by 1 µM NE. A low concentration of SKF96365 that did not affect thapsigargin-induced store-operated Ca2+ entry blocked 60-70% of the NE-induced Ca2+ entry. Two different calmodulin inhibitors (W-7 and trifluoperazine) also blocked the NE-induced Ca2+ entry. These data suggest that in addition to L-type channels, NE primarily activates ROCs rather than SOCs in ILAs, and that this receptor-operated Ca2+ entry mechanism is regulated by calmodulin. Interestingly, 2-APB completely blocked the NE-induced non-L-type Ca2+ entry, implying that SOCs and ROCs in preglomerular resistance vessels share a common molecular structure.
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