Calmodulin mediates norepinephrine-induced receptor-operated calcium entry in preglomerular resistance arteries

Abstract

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 dose dependently blocked by the SOC antagonists Gd3+and 2-aminoethoxydiphenyl borate (2-APB) and the combined SOC/ROC antagonist SKF-96365. Gd3+had no effect on the non-L-type Ca2+entry activated by 1 μM NE. A low concentration of SKF-96365 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.