NAADP contributes to norepinephrine and endothelin‐1‐mediated Ca2+ stimulation in rat renal afferent arterioles

Nicotinic acid adenine dinucleotide phosphate (NAADP) may be produced by ADPR cyclase residing in acidic vesicles in response to G protein‐coupled receptor (GPCR) stimulation in vascular smooth muscle cells. We tested the hypothesis that NAADP receptors mediate increases in cytosolic Ca 2+ ([Ca 2+ ] i ) induced by norepinephrine (NE) and endothelin‐1 (ET‐1) in isolated renal afferent arterioles via a lysosome‐dependent pathway. To test this, we measured [Ca 2+ ] i responses to NE and ET‐1 in individual arterioles of Sprague‐Dawley rats. ET‐1 increased peak [Ca 2+ ] i by 100‐130 nM. This response was attenuated by lysosome disrupters concanamycin A1 (CCA) and bafilomycin A (Baf) to 58 ± 8 and 64 ± 10 nM, respectively (P < 0.05). The NAADP receptor inhibitor N AADP E ON d iscovered molecule 14 (Ned‐14) reduced ET‐1 stimulation to 34 ± 11 nM (P < 0.005). Control NE increased immediate [Ca 2+ ] i 70‐80 nM. CCA and Baf decreased the response to 37 ± 3 and 47 ± 7 nM, respectively (P < 0.05). Ned‐14 decreased NE responses to 25 ± 8 nM (P < 0.005). We conclude that NAADP receptors and lysosomal vesicles contribute to Ca 2+ signaling pathways evoked acutely by ET‐1 and NE in renal afferent arterioles.